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nissan rb overheating under high load.

Off Topic Discussion

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Input on a overheating issue please,

Ive got a Rb30det that i cannot seem to keep the coolant temp. stable under high load.

Motor rebuilt ( pressure tested head and block before building) say 7 - 9 track days old, New mishismoto radiator , fans and thermostat. New head gasket and studs.

New waterpump, air removed from system , rad cap new etc.

Drift Days , Normal driving and traffic no problem, fans cycle and everything is good.

Circuit race days it will start to overheat.

Back straight of puke it will start to creep up past 100 and also when TPS maping on the dyno it will do it.

The mishimoto rad is only a single pass type? will getting a duel pass help or modifing the mishimoto rad to have to flow twice though before entering the engine? Or changing the outlet to the otherside of the rad?

Will going back to the factory clutch fan and shroud help?

Thanks in advance.

I always try and use the factory viscous fan with cowling on JZ and RB engines, mostly for the rad bur also for the amount of air circulating the engine bay.

Have you tried a leak down test of the chambers?

Yes i carried out a leak down test and it was good, no problems.

The radiator overflow bottle never overfills and works correctly aswell, theres not excessive pressure in the cooling system.

I dont think my cooling system is up to the job, im just looking for ideas.

I'm always suspicious with any turbocharged engine that overheats under sustained load of the head gasket integrity. If the engine is lifting the head under boost, you will have it push water out into the overflow and the temp will increase. Often these engines will still seal perfectly well under light load giving no indication of a problem. You should see signs of this by the water level dropping and the overflow filling though, which it sound like it isn't in your case.

Of course this isn't the only possibility. Our Toyota 86 struggles to control temperature on the track and I've personally put this down to a lack of airflow out of the engine bay. It's not enough to have airflow onto the radiator - The air also needs to be able to escape out of the engine bay.

I'll agree with Chris that the factory radiator shroud and viscous fan arrangement seem to be a great solution for cooling on an RB, however at race track speed you are relying on airflow rather than the fan for cooling - The fan is more critical at idle and cruise.

I just did the headgasket and new head studs. Block and head both machined six months ago.

With the the rb radiator design with the inlet and outlet both on the same side ( drivers )

Does the waterflow though the whole of the radiator or just the drivers side 1/3 of the radiator , the area around the inlet and outlet? path of

lowest resistance. Not using the complete surface area of the radiator to cool the water or the water passing though the radiator too fast and not being cooled.

The water goes into the bottom tank end of the rad and passes through the entire radiator unless there's air in the system, then fills the top tank and exits the hose.

What pressure does your leak down tester run at?

Have you tried running without a thermostat?

is there any obstructions to the front of the rad?

Just wondering if Chris is onto something with regards to air being caught in the system.

You don;t say what type of car the engine is in but I know VL Commodores could get air caught and be fine with normal running but when pushed they got very got very quick. The issue was because the VLs radiator was a bit lower than the top of the water jacket so to make sure you got all the air out you would jack up the front of the car to make sure the radiator fill (and top hose) were above the cylinder head. Didn't need to go up much, 1" often sufficed.

yes its been bleed correctly, theres no air in the system.

In front of the radiator is a intercooler and oil cooler. could the oil cooler be causing it to get hot? oil temp is around 110 degrees give or take.

Chris see my drawing of the radiator. Could it not be using the complete radiator as the two in and outlets are on the same side and

there nothing in the radiator to make it flow though the complete cooling area? sorry, kinda of bad drawing and explanation

Attached Files

I've dealt with a similar issue with a customers s14 that we put a 1jz into it, on track days the temps would start to rise. The car also had a engine oil cooler and intercooler in front of the radiator. We built a fan shroud and fit the factory 1jz clutch fan back into. The shroud we cut out little vents into it, so when at speeds the airflow will help get rid of the heat through the shroud, instead of only relying on the one big exit where the fan is located. On track days we install spacers for the hood to help get rid of the hot air from inside the engine bay. The car went from running 220-230 F to 200-205 F. Even adding a swirl pot in the coolant system will help.

To diagnose we need to test for temp drop across the radiator. Temp in and temp out. If less than 8 degrees Celsius across the cooler we have a high flow issue or an inefficient cooler. This could also be an airflow issue.

If the drop is higher we may have a restriction in coolant flow or a failing water pump.

Removing thermostats, messing with head gasket coolant ports or modifying cylinder head coolant galleries can make the coolant flow too quick and not allow adequate time for the heat to exchange from the head into the coolant.

what fan shroud are you using ? i see people overheating whith the closed plate dual mishimoto fan setup like in this picture

if you have this setup , simply remove it , will be much better

Attached Files

Pronto, if you see my drawing of the rad flow you'll see how there is no circulating as your fearing.

Do you have any ducting to channel air directly into your rad? I have seen many a big mouth fronted cars having high speed cooling issues from this as they didn't have any ducting to their coolers and the air circulated or escaped around them instead.

See photo attachment of a twinsturbos built supra getting the ducting to cool everything evenly, it really is a work of art

Attached Files


my approach would be as follows:

check coolant level / trapped air.

test radiator cap

test thermostat

rule out head gasket or a leak.

add ducting to direct air into radiator.

if you have a spare boost gauge you could take a pressure reading in the shroud, if you see a positive pressure at high speed look at adding diversion around the fan (cut out one-way flaps etc.)

space bonnet.

vented bonnet.

pretty much start simple and cheap and work through to the most expensive and difficult things.

ducting is a big issue at speed both inlet and outlet have a large affect.

Also replace the oil cooler radiator if it`s in front of the main radiator. Are you sure that the water doesn`t mix up with oil or exhaust gases?

Sometimes it happens on properly functioning engine with extreme loads applied, when the water cavitation occuring on the pump wheel, or heat carrier boils in most heated parts of the cylinder block. R6 engine is not ideal in the side of heat exchange uniformity with heat carrier. The serious sport prepaired engines carry breather tanks in order to separate gas from heat carrier hence improve the heat exchange. Ask Google "Jun cooling lines, or Jun breather tank"