- Coolant temperatures are not an accurate indicator of metal temperatures. The coolant's maximum temperature is it's pressure corrected vapor point. The metal can be several hundred degrees hotter than the adjacent coolant.
- Temperatures of critical areas must be determined by checking the metal at a controlled distance from the combustion chamber surface. This eliminates discrepancies caused by the variances in metal thicknesses.
- Higher coolant flow will ALWAYS result in higher heat transfer. Coolant cannot absorb heat after it reaches it's pressure corrected vapor point. Furthermore, coolant absorbs heat at a progressively slower rate as it approaches this point
Following is a typical engine:
Inlet temperature = 180 F
Outlet temperature = 190 F
Coolant flow = 100 GPM
Specific heat of coolant = 1.0
1 HP = 5.2769885 GPM 1 F
{ (Outlet-Inlet)CS} / 5.2769885 = HP loss
{(190-180) 100*1.0} / 5.2769885 = 189.5 H
Cooling System
- Radiator
- Coolant Temperature Sensor 2 wire and 1 wire
- Aftermarket Radiators
- Radiator Cap
- Thermostat
- Water/Fluid/Coolant/Anti Freeze/Glycol/Cooling Medium
- Overflow
- Swirl Pot/High Side Breather/Bleeder
- Hoses
- Fan
- Fan or Radiator Shroud
- Fan Testing
- Ducting
- Water Pump
- Oil Cooler
- Intercooler
- Tuning/Ignition timing
OEM Radiator
 |
| OEM R32 GT-R radiator with aftermarket upper radiator hose, and a Nismo radiator cap. |
The purpose of the radiator is to transfer waste heat energy captured by the cooling medium, and transfer it to the air. The OEM R32, and R33 radiators have composite or plastic end tanks. The early R34 have all aluminum radiators. However the later ones, 2000 up go back to composite/plastic end tanks. I asked Tamura about that, and he said in order to get the carbon fiber hood on the later cars, to save money elsewhere, the radiator went back to composite end tank. Give and take, even in the OEM world.
Coolant Capactiy (liters)
| RB20/RB25DE/RB25DET | RB26DETT |
|---|
| Capacity | ~9 | ~9.2
|
|---|
 |
| Nissan Skyline Radiator Cooling System Fill and Bleed Procedure |
Thicker radiators do have slightly more airflow resistance than thinner radiators but the difference is minimal. A 4″ radiator has only approximately 10% more airflow resistance than a 2″ radiator.
In past years, hot rodders and racers would sometimes install a thicker radiator and actually notice decreased cooling. They erroneously came to the conclusion that the air could not flow adequately through the thick radiator, and therefore became fully heat-saturated before exiting the rear of the radiator core. The actual explanation for the decreased cooling was not the air flow, but the coolant flow. The older radiators used the narrow tube design with larger cross section. Coolant must flow through a radiator tube at a velocity adequate to create turbulence.
The turbulence allows the water in the center of the tube to be forced against the outside of the tube, which allows for better thermal transfer between the coolant and the tube surface. The coolant velocity actually decreases, and subsequently its ability to create the required turbulence, in direct relation to the increase in thickness. If the thickness of the core is doubled, the coolant velocity is halved. Modern radiators, using wide tubes and less cross section area, require less velocity to achieve optimum thermal transfer. The older radiators benefited from baffling inside the tanks and forcing the coolant through a serpentine configuration. This increased velocity and thus the required turbulence was restored.
Radiators with a higher number of fins will cool better than a comparable radiator with less fins, assuming it is clean. However, a higher fin count is very difficult to keep clean. Determining the best compromise depends on the actual conditions of operation.
Double pass radiators require 16x more pressure to flow the same volume of coolant through them, as compared to a single pass radiator. Triple pass radiators require 64x more pressure to maintain the same volume. Automotive water pumps are a centrifugal design, not positive displacement, so with a double pass radiator, the pressure is doubled and flow is reduced by approximately 33%. Modern radiator designs, using wide/thin cross sections tubes, seldom benefit from multiple pass configurations. The decrease in flow caused by multiple passes offsets any benefits of a high-flow water pump.
Cross flow radiators are superior to upright radiators because the radiator cap is positioned on the low pressure (suction) side of the system. This prevents the pressure created by a high-flow water pump from forcing coolant past the radiator cap at high RPM. As mentioned in the radiator cap section, an upright radiator should be equipped with radiator cap with the highest pressure rating recommended by the manufacturer. The system will still force coolant past the cap at sustained high RPM.
Coolant temperature sensor 2 wire and 1 wire
The 2 wire sensor, is the sensor that the ECU uses as an input. It is a very important sensor. It effects startup, and running of the car. We often see the cooling system not bled right, and an airpocket forms at the sensor. When this happens, the sensor may show 250F-300F. When this happens, the ECU thinks the car is hot, and it may not fire the injectors, based on the tune. So if you have hot start problems, that go away once you crank for a bit, the CTS is a good thing to look at, then the bleeding. This gets back to having a
Consult datascanner, so you can see what the ECU is seeing. Makes troubleshooting much easier.
OEM two wire aka ECU input
22630-44B20 (fits about 50 different Nissans)
The 1 wire sensor only drives the gauge in the dash. A cool fact, R32 and R33 are different resistances. You find these things out later, when you start a car up, and have the wrong sensor in. Then about 2 minutes in, the gauge pegs, the car is fairly cool. NZ EFI says that the R34 is also different, need to look that one up.
Aftermarket Radiators
 |
| Factory all aluminum radiator on an early R34 GT-R |
Please don't buy a crappy radiator. The stock one probably does a better job, fits better, allows the use of the fan shroud, and won't leave you stranded. I don't care what kind of warranty they offer, only buy from trusted brands. Most aftermarket radiators are aluminum. Honestly aluminum is not the best conductor of heat. Copper/Brass is a better conductor,
but if you built one that worked well, it would be so heavy, it would probably outweigh any benefits. More information about
copper vs aluminum radiators. Flex a lite has this to say about
copper vs aluminum vs their radiators. In the end copper while in theory works better to transfer heat, in the real world, it isn't durable, light enough, or pressure resistant enough to work in an automotive environment.
Heat rejection is the term for measuring the ability of a material to transfer heat to the air. This is what a radiator's job boils down to: Take engine heat that has been transferred to the engine coolant and transfer it to the atmosphere. Heat rejection is measured by the amount of British Thermal Units (BTU) per hour the system can dissipate. Higher BTU/hour means more heat transfer and better cooling.
Brass radiators came in nearly all vehicles until the '80s. A typical original-equipment brass radiator rejects heat at a rate of about 1,500 BTU/hour. That's pretty good, and this is why brass was chosen as the material for radiators. In the '80s, car manufactures wanted to reduce costs and lower vehicle weight. This led to changing the radiator design to use composite (plastic) tanks with an aluminum core. The plastic tanks transfer about 1,000 BTU/hour; considerably less than the traditional brass construction. Next we come to aluminum radiators. It might surprise you to learn that the typical, smooth aftermarket aluminum radiator tanks dissipate heat at a rate of about only 700 BTU/hour! That's less than half the BTU of brass sidetanks!
 |
| Leask Spec Radiators - triple bypass mod and non triple bypass mod side by side |
Radiator flow. So you have your normal type flow which is top end tanks, and the inlet and outlet on the same side. Then you have something like what is called a cross flow, where the inlet is on one side, and the outlet on the other side of the radiator.
The radiators above, modified by Leask Spec, have some cool features. One has what is called a triple bypass mod. By making the coolant spend more time in the radiator, you can usually control the amount of heat it will give up to the atmosphere. In addition to that mod on one of the radiators, he also puts an electric fan, and rubber flapper doors in a shroud.
 |
| Rubber flapper doors are closed at idle, but open to allow air to pass through at speed. |
Koyo -
Koyos have been around a long time. They are a well priced radiator that fit like stock, and just work. If you are on a budget and looking for something good, this is your radiator.
C&R - These guys build NASCAR radiators. We had them build us a radiator for the R34 GT-R race car when we ran World Challenge. Their stuff is top notch. C&R is actually part of the PWR Group now.
https://www.crracing.com/aftermarket
CSF-
We worked with CSF on a billet end tank radiator for R32's. The 2-Row 42mm core not only increases the fluid capacity of the radiator, but also greatly improves the cores ability to dissipate heat. CSF’s Exclusive B-Tube Technology increases the heat transfer by approximately 15% over typical oval welded tubes. In addition, the super-efficient multi-louvered fins maximize airflow through the core for the best possible performance. The greater amount of cooling rows improve the overall efficiency of the radiator, while more cooling tubes increase the surface area for the coolant’s heat to dissipate.
PWR- These Aussies build some good parts. Another well liked, raced, and proven part.
https://www.pwr.com.au/products/radiators/radiators-faq
https://www.pwr.com.au/portfolio/nissan-car-radiators
HPI - They are popular in Japan
ARC - Awesome parts, expensive, but some stuff is worth it.
Nismo - They source some of the best parts. Expensive, but may be worth it to you.
Ron Davis - Located in Arizona, Ron Davis made us an R32 GT-R Radiator in the past. They don't list one, but you can probably call and ask, or draw them up for them to make for you. -
http://www.rondavisradiators.com/radgallery.htm
Radiator Cap
 |
| Nismo old logo radiator cap. This one is 1.3 kg/cm2 or 18.4 psi cap |
The radiator cap is a relief valve. It has a spring,and it allows pressure to build in the cooling system, until the pressure overcomes the cap. The higher the pressure in the system, the higher the boiling point of the fluid/medium. As the pressure of the cap goes up, also the stress on the cooling system goes up. The RB26 has a ton of coolant lines under the collector. You really don't want to stress test every single one of those connections by putting a cap with excessive pressure on it.
21430-4B700 0.9 bar (13 psi) OEM R32
21430-7999C 88 kPA (12.7 psi) Superceeds 21430-4B700
21430-54P00 1.2 bar (17.4 psi) 300zx
Koyo SK-C13 1.3 bar (18 psi) radiator cap.
Nismo 1.3 bar (18 psi) radiator cap
In a cooling system, a higher pressure equates to a higher boiling point for the coolant. Higher coolant pressures also transfer heat from the cylinder heads more efficiently. We recommend using a radiator cap with the highest pressure rating that the radiator is designed to accept. In general, performance radiators will accept 22-24 PSI, and professional racing radiators will accept a 29-31 PSI.
https://www.stewartcomponents.com/tech-tips/tech-tip-2-radiator-caps/
| Absolute pressure | Water boiling point |
[bara]
[1x105*Pa] | [psia] | [mm Hg] | [in Hg] | [°C] | [°F] |
| 1.013 | 14.7 | 760 | 29.92 | 100 | 212 |
| 1.034 | 15.0 | 776 | 30.54 | 101 | 213 |
| 1.103 | 16.0 | 827 | 32.58 | 102 | 216 |
| 1.172 | 17.0 | 879 | 34.61 | 104 | 219 |
| 1.241 | 18.0 | 931 | 36.65 | 106 | 222 |
| 1.310 | 19.0 | 983 | 38.68 | 107 | 225 |
| 1.379 | 20.0 | 1034 | 40.72 | 109 | 228 |
| 1.517 | 22.0 | 1138 | 44.79 | 112 | 233 |
| 1.655 | 24.0 | 1241 | 48.86 | 114 | 238 |
| 1.793 | 26.0 | 1345 | 52.94 | 117 | 242 |
| 1.931 | 28.0 | 1448 | 57.01 | 119 | 246 |
| 2.068 | 30.0 | 1551 | 61.08 | 121 | 250 |
| 2.206 | 32.0 | 1655 | 65.15 | 123 | 254 |
| 2.344 | 34.0 | 1758 | 69.22 | 125 | 258 |
| 2.482 | 36.0 | 1862 | 73.30 | 127 | 261 |
| 2.620 | 38.0 | 1965 | 77.37 | 129 | 264 |
| 2.758 | 40.0 | 2069 | 81.44 | 131 | 267 |
Thermostat
A thermostat is a flow control valve. It opens/starts to open at a certain temp, and it allows for coolant flow though the radiator. The OEM thermostat is the same as the VG.
OEM Thermostat opens at 76.5C or 170F.
21200-42L0A
Stant 45947 SuperStat
A cooler rated thermostat, does not make your car run cooler in most cases. What it does, is open at a lower temperature, but once its fully open, its up to the rest of the system to keep the car cool.
Water, Coolant, Anti-Freeze, Cooling Medium
Water is better at transferring waste heat energy than coolant. However glycol has a higher boiling point than water. Check out this article from
Hot Rod Magazines Marlan Davis.
The specific heat capacity of ethylene glycol based water solutions is less than that of pure water; in a 50 percent solution, ethylene glycol's specific heat capacity compared with pure water is decreased at least 20 percent at 36 degrees and about 17 percent at 200 degrees. Propylene glycol, another common coolant, has an even lower specific heat. Assuming a 100-gpm (gallons/minute) coolant flow rate and an energy loss through the coolant system of 189.5 hp, the water temperature increase would be 10 degrees, the ethylene glycol water mix would gain 20 degrees, and propylene glycol would gain 33.3 degrees.
I run water and water wetter in my cars. Many tracks don't like you to run glycol as its much harder to clean up than water. Some people run distilled water, some run tap water. There are a few theories out there. In the end you do have dissimilar metals in the system, that will cause some amount of galvanic corrosion. So you do want some kind of additive in the system. If you are anywhere that it freezes, or transporting your car though anywhere that freezes, you want to put some glycol in it.
During the distillation process, water is vaporized into its gaseous phase, so all its impurities are left behind. These impurities include a number of minerals, including “calcium” and “magnesium,” the two components of water “hardness.” The water is then condensed back into its liquid phase, so the resulting liquid is pure water – in fact, some of the purest water on earth. But the problem is that when water is distilled, or “stripped,” of its minerals and impurities, the resulting solution is composed of chemically imbalanced “ions.” This leaves distilled water “ionically hungry,” so it will actually strip electrons from the metals in a cooling system as it attempts to chemically re-balance itself. As it chemically removes electrons from the metals of cooling system components, distilled water eventually does extreme damage that could lead to cooling system failure.
So what’s the answer? Softened water. During the water softening process, the same impurities and minerals are removed from water as during the distillation process – but with one very important distinction. Rather than STRIPPING the impurities from water, softening EXCHANGES the impurities with a sodium ion. The resulting solution is chemically and ionically balanced, making softened water very stable, very pure, and non-threatening to cooling system metals.
There seems to be a perceptual issue with regard to the usage of softened water in cooling systems by auto enthusiasts. Many mistakenly believe that because salt is added to water softeners, then softened water must contain salt, a substance of course known to be very corrosive. Nothing could be further from the truth. The salt you add to a water softener is NaCl, or sodium chloride.
In the past, we have experimented with waterless coolant, like
Evans NPG. The theories are great, but never saw anything that said- this is 100% the way. Will explore that again in the future.
Inorganic Acid Technology or IAT: This is the common green stuff original equipment manufacturers have used for over 70 years. Ethylene glycol is its base chemical and there are silicate and phosphate additives that make it compatible with copper, brass, cast iron and aluminum cooling system components. Manufacturers recommended that you change the green IAT antifreeze every 36,000 miles or three years. IAT coolant was used in GM vehicles until 1994. Chrysler used green IAT fluid until 2001 as did Ford, (with the exception of some 1999 models that used OAT blue coolant which must be purchased from Ford).
 |
| This chart is for an R34. Notice that the engine oil, and front and rear gear oil recommendations are based on ambient temperature. If you live somewhere cold, you want a thinner fluid if you drive in cold temps. If you live somewhere hot, you want a thicker fluid to help protect when it is hot. |
Hoses
 |
| Hoses from HPS |
R32 GT-R
Upper Radiator Hose
21501-05U00
Lower Radiator Hose
21503-72L00
So what do you do, if you just lost a hose, on the side of the road in the middle of nowhere? You can always take the old hose to an autoparts store. They normally have racks of hoses. Find one with a similar shape, or a section with a similar shape, and cut to fit. You can also use a hose repair kit, to at least get you back on the road.
 |
| Red coolant hoses from HPS, remember kids, red is faster |
There are a ton of hoses under the collector, a few that run behind the engine, and then you have the turbocharger coolant supply and return. There are a lot of places that coolant can leak from an RB. None of them particularly fun to fix.
Overflow Tank
Overflow cap - these seem to leap away from you, when you remove them. A new one is only $3.
Swirl Pot/High Side Breather/Bleeder
There is a 10mm bolt (M6 x 1.0 thread) on the forward part of the balance tube, that you use to bleed the air out of an RB26. Caution. if you loosen it too much, or don't realize what you are doing, boiling hot liquid will come out. The 10 mm bolt will drop down into the engine/collector abyss, and you will be wondering why you did, what you just did.
Over the years I have seen some pretty crazy high side venting of the head. As the engine is tilted, some people think that it is very important to have extra bleed ports on the intake side of the head.
JUN used to do a pretty insane setup.
Fan
I like the stock clutch fan. Lots of people ask about electric fans, but honestly I have not(yet) seen an electric fan, that works good enough to replace the stock clutch fan. At speed, the fan really shouldn't be doing anything, but at idle, with the air conditioning on, in hot temperatures, you need that fan to move as much air past the air conditioning condenser, and through, not around the radiator as possible. The stock fans crack around the base. Inspect your fan, if its 30 years old, it probably needs to be replaced.
If you are going to replace your stock clutch fan, check the clutch for proper operation, and an R34 fan is a good upgrade for R32, and R33.
 |
| Stock clutch fan bimetallic strip position hot |
 |
| Stock clutch fan bimetallic strip position cold |
These are not the only fans you see on the RB26, but here are most of them. Along with the several styles of OEM, GK Tech also does an aftermarket fan. Some people have broken the GK Tech fan, but I do believe its just because their engine is rocking. The material of the GK Tech fan is a little thinner, and not as forgiving as the OEM fan. The OEM will wear down/grind down. The GK Tech will break. Overall its a sign you have a bad mount or something just isn't lined up right.
Clutch coupling R34 -21082-24U00 (
21082-RHR30 Nismo Heritage)
https://www.flex-a-lite.com/blog/the-truth-about-airflow-and-amperage/
GK Tech sells a replacement fan they say flows 40% more air than stock. We have one on the #bluecar
The GKTECH high-performance engine fan has been designed and engineered in Australia with the intention of pulling more air than the factory item.
When tested on a dyno the GKTECH high-performance fan took less than half the time to cool down from 90 degrees to operating temperature (good for next time you're on the start line at the track).Super easy to install, simply remove your factory fan (4 bolts) and install the new fan, it is a direct replacement clutch fan to suit SR, KA, RB, VG enginesAn adapter is needed to fit RB/VG engines, as seen here: - Direct replacement of the standard fan- Pulls 60% more air than the factory SR fan- Pulls 40% more air than the factory RB fan
Electric AC fan testing
Fan or Radiator Shroud
If you don't have a damn good reason to remove the shroud, DON'T. If you don't know what it does, then DON'T remove it. If your radiator makes it not possible to mount a shroud, return that POS ebay special, and get a radiator that allows a shroud. If your radiator is too thick to allow a shroud and fan package, then that is for you and god to sort out.
The R35 has great ducting, and even some cool features, like the flapper doors on the fan shroud. Anything blocking airflow could cause a choke point, so Nissan designed the shroud with doors that stay closed at low speed. Then the electric fans are more efficient. At a point air pressure will overcome the doors resistance and the doors will open. It is pretty basic, but cool to nerds that notice things like this.
 |
| R35 fan shroud with dual fans and flapper doors. |
 |
| R35 fan shroud with dual fans and flapper doors. |
 |
| R35 fan shroud with dual fans and flapper doors. |
Ducting
 |
| R32 GT-R radiator lip, this one is aftermarket and superior to the OEM Nismo lip spoiler |
Air must go through the core for the radiator to do its job efficiently. Read this paper on ducting and its effects on cooling.
https://www.beta-cae.com/events/c1pdf/05_chacko_radiator_efficiency_paper.pdf
 |
| We were running the Garage Defend radiator panel in the blue car. This panel extends all the way across, behind the headlights |
Air wants to take the path of least resistance. We want it to pass through the radiator core. A radiator panel will help to direct air from the grill though the core. The more sealed the better, but not always practical.
 |
| R34 race car with ducting. Carbon fiber side ducts. Lower ducting you can see here. The top panel is removed. |
 |
| R34 side and lower ducting is visible here |
 |
| Side ducting from the top |
 |
| Lower ducting |
 |
| The other side of the ducting and the C&R radiator. Yes this car has no shroud, I know. It isn't a street car. |
 |
| OEM R34 foam, trying to make air pass through the core |
 |
| OEM R34 foam, trying to make air pass through the core |
 |
| OEM R34 foam, trying to make air pass through the core |
 |
| Leask Spec Radiator Ducting. This is super important to help airflow though the radiator. A crappy radiator with ducting, is better than the best radiator with none. |
 |
| Leask Spec Radiator Ducting. This is super important to help airflow though the radiator. A crappy radiator with ducting, is better than the best radiator with none. |
 |
| Leask Spec Radiator Ducting. This is super important to help airflow though the radiator. A crappy radiator with ducting, is better than the best radiator with none. |
 |
| Leask Spec Radiator Ducting. This is super important to help airflow though the radiator. A crappy radiator with ducting, is better than the best radiator with none. |
 |
| Leask Spec Radiator Ducting. This is super important to help airflow though the radiator. A crappy radiator with ducting, is better than the best radiator with none. |
Water Pump
 |
| Can you describe the shape of the water pump gasket for us? Oh no gasket, just liquid gasket |
Water pump
Water Pump - 21010-21U26
N1 Water Pump - 21010-24U27
 |
| N1 water pump in the background, normal in the forground. Notice the top bolt hole. This is an issue if you dont have an N1 block. It can be filled in a number of ways. Just make sure you do it before you install it. |
So some people say they have problems with N1 water pumps at idle. Over the years, not anything that we have noticed, but we are investigating it. The N1 pump has less blades, but they are larger, and it has a anti-cavitation plate on it. Cavitation causes weird things to happen, like bubbles, so you want to minimize that if possible.
I have to look up if there are flow numbers for the water pumps anywhere. I looked into a flow tester at one point, but never got much further than that. We have a friend that runs an electric water pump with a rear mount radiator in a drift car, and although it sounds like it would be the way to go, so far it seems to be pretty far from that. Someone posted some
Reimax information on water pumps. Reimax was involved with the Group A cars.
"We have commercialized a prototype for race engine development. By brushing up the impeller shape, a high flow rate that exceeds not only the STD but also the N1 specifications is realized, and the cooling performance is improved by increasing the amount of circulating water in the radiator. It also leads to further improvement in cooling efficiency of sports radiators with increased capacity."
|  STD |  N1 |  HIGH FLOW |
| Outer diameter | φ64 | φ70 | φ70 |
| feathers | 8 | 6 | 8 |
| Shroud | N/A | A | A |
| Discharge rate | 160ℓ/min | 192ℓ/min | 221ℓ/min |
Water pump flow rates and pulleys From Skylines Australia
Oil Cooler
 |
| RB factory oil cooler. Coolant lines are green. |
On a stock RB26 there is an oil/water heat exchanger on the right side of the engine. The oil filter attaches to part of the assembly. If you have an R32 with Hicas, you know how fun it is to get to the oil filter.
You have a lot of factors that contribute to oil temperature in an RB26dett. It is honestly near an oil cooled engine. The higher you rev it, the more temperature you add. At a point you can't cool the oil enough, and it breaks down. When it breaks down enough, you kill an engine. An RB26 has a long crankshaft with 7 main bearings. Each bearing is adding lots of heat at high rpm. Cams, turbos, oil squirters, and more.
More oil cooler information here
Intercooler
The
intercooler plays into the radiator as its a major component that blocks airflow to the radiator. It is also a heat exchanger, but air to air in most cases. The biggest thickest intercooler, may cause your car to overheat, especially if the air isn't ducted after the intercooler.
 |
| Factory intercooler and ARC oil cooler on the R34 race car. |
Tuning/Ignition Timing
If you don't run enough advance in the ignition timing, you can cause overheating issues. If you use a lot of the two steps, as the cool kids do these days, with things like anti-lag you will put a ton of heat into the cooling system. Plan your days accordingly.
Buy USA Legal R32 Skylines at
Buy-R.com for Nissan Skyline GT-R and GT-R parts.
This page isn't done yet, but I am done working on it for now. I think it has a lot of useful information, but it will be expanded in the future. - March 2020.
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