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RB20 R32 Overheating

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Hi guys,

Looking for some help from the brains trust again please.

Recently the RB20 in my 32 overheated, I was able to limp it home and discovered absolutely no coolant in my radiator and steam pissing out of the overflow.

Since then, I have flushed the block and the radiator. We discovered that the heater box was blocked so until I can replace that we have deleted it by removing the hoses from the firewall and connecting them to each other. Filled up with coolant and demineralised water and have bled it on a number of occasions for 30-60 minutes.

Now I can still drive the car but after about 30 minutes the temp guage starts shooting up and I'm at a bit of a loss as to why.

The thermostat appears to be working as the lower rad hose does warm up with the rest of the engine. I'm not losing/leaking any coolant. No oil in coolant or vice versa and my mechanic friend has performed a head check which didn't indicate any gasses passing into the coolant. I've also replaced the radiator cap with a brand new GKtech one (which I have happily used on all my cars without issue)

At this point I'm considering the following:

  • Running radflush through the radiator and engine.
  • Replacing radiator and thermostat.

Anyone have any other thoughts or suggestions? TIA



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Have done a few different things.

First - Left the car running for 45 minutes with bottle stuck in the open radiator cap and slightly filled the bottle so that the highest point was above the top of the engine. occasionally blipping the throttle until bubbles stopped coming out.

Second - Started same as above but left the radiator cap on and cracked the bleed valve on top of the intake plenum until bubbles stopped coming out of there.

Did those two a few times.

Finally - Basically the same as #2 but drove the car around, brought it back into the garage and cracked the bleed valve until no bubbles.


Happy to take suggestions on any other methods I should be trying.

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Stock radiator with shroud and gktech clutch fan (which is working).

Nismo thermostat but this was installed >5 years ago

It had been running fine with these for quite some time until the empty radiator incident.

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But now that you mention it, I haven't confirmed that the clutch fan is still spinning once the temp starts climbing though. Might do that tonight.

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9 minutes ago, Dose Pipe Sutututu said:

maybe also pop the stock fan blade back on

17 minutes ago, 32_love said:

gktech fan

8 minutes ago, 32_love said:

Can't hurt to try.

This is where I'd start. I like GKTech stuff, but there are more reports of that particular fan not working on RBs than there are reports of it being even as good as stock, let alone better.

Also, inspect the radiator. How are the fins? If many are bent over, then you will suffer.

Also look at the overall air path from grille through to the radiator core. Is it set up to allow air through the front mount to just spill out the bottom instead of going through the rad? Some corflute sheeting might help.

Edited by GTSBoy
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I'd be re-doing the head gasket check(Combustion leak), can be very subtle and given how long it takes to overheat, likely a small break in the head gasket. 

Agree the gktech fan needs to go but assuming you are in brizzy it should hold up to 25degree weather.


Out of the 5 or so times I've had this problem, only once was I lucky enough to have a stuck thermostat. 

The rest, pull the head off fun times. 

I hope for you this is a lucky one :)

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On 30/04/2024 at 8:48 PM, Butters said:

I'd be re-doing the head gasket check(Combustion leak), can be very subtle and given how long it takes to overheat, likely a small break in the head gasket. 

I agree, particularly if the test was done before the engine was warmed up (which is how you would normally do it so you don't burn yourself).

Have you confirmed it is not loosing coolant since the first instance?

Also, has the overheating after a while thing only been happening since it got hot, or did it do so before that as well?

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We let the engine warm up as much as it could while stationary and with the head check plugged into the open radiator but I see you're point that it would be difficult to get it to the point where it begins to overheat.

The overheating issue only began after the initial problem with the empty radiator. Until then I had driven the car almost daily without any issues (with the gktech fan etc.)

I'm beginning to suspect butters may be right and that it's a head gasket issue, just difficult to find the time to work on the car lately. And whether or not it's even worth doing the head gasket etc. on the 20 when I am, extremely slowly, building a 25 for this car.

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