Rb26 Running Hot

[God_speed]

Thanks Mick. Will do. The top hose has been firm when I've checked it previously when the car is up to temp. I've never monitored how much the cap is giving up to the overflow though, under pressure.

For reference and anyone else wanting to know, the OEM Nissan part number for the regular thermostat is 21200-42L0A.

Thanks to Wongy for linking me up with a good source.

[Gts-t]

No problems Matt, hopefully this info can help others too. I also never bother checking the overflow when its hot, only when its cold.

Let us all know how you go with getting it sorted.

[djvoodoo]

I'm no engineer, so may be completely way off.. But i always find when turning the car off, after a few mins my temps reach 105 degrees, and I can here and feel boiling on the top radiator pipe.

Have not lost any coolant whatsoever since last coolant change 7.5K ago.

Is this thermosyphoning properties? Once the turbos stop spinning the water goes back to the head and hits the temp sensor on the thermo side, therfor creating a "false" overheating??

[GTRPSI]

Thats the hot water rising to the top as its no longer being pumped around, start the car and get the water pump working and it mixes with the cooler water dropping the temp back down.

[jjman]

I'm no engineer, so may be completely way off.. But i always find when turning the car off, after a few mins my temps reach 105 degrees, and I can here and feel boiling on the top radiator pipe.

Have not lost any coolant whatsoever since last coolant change 7.5K ago.

Is this thermosyphoning properties? Once the turbos stop spinning the water goes back to the head and hits the temp sensor on the thermo side, therfor creating a "false" overheating??

it shouldn't be boiling after shut off. The only sound you should hear is when the pressure in the system causes the coolant to push past the cap into the overflow bottle (but this doesn't happen much and it unlikely you will frequently catch the system doing this).

if it is making a boiling sound after shut off its most likely because your cap isn't pressurising the system sufficiently to raise the boiling point so it indeed doesn't boil at 100-105 degree range. Secondly, that you have airlocks in the system similarly causing reduced pressure and boiling at 105,

Also, does 105 degrees after shut-off seem a little high to anyone? I had a digital temp gauge on my car and the most it got to was 90-95 after shutoff... Though I did have a 52mm alloy radiator in it.

[Victory]

I recently had an intermittent water temperature issue in one of my Skylines where the radiator cap would not always pressurise the system correctly. This problem took some time to identify and resolve.

With the radiator cap on and the engine cold if you squeezed the top radiator hose no coolant would come out of the system (i.e. the system was pressurising correctly). However, for no obvious reason you could sometimes squeeze the top hose and coolant would pass through the overflow pipe into the overflow bottle.

I inspected the cap on numerous occasions and could not see any obvious reason for this intermittent pressure leak. I then replaced the cap and have not had the problem since.

[God_speed]

Thanks for your input Charles.

[Humbla]

I put a new cap on my 25 every 2 years,cheap as . :-)

[djvoodoo]

it shouldn't be boiling after shut off. The only sound you should hear is when the pressure in the system causes the coolant to push past the cap into the overflow bottle (but this doesn't happen much and it unlikely you will frequently catch the system doing this).

if it is making a boiling sound after shut off its most likely because your cap isn't pressurising the system sufficiently to raise the boiling point so it indeed doesn't boil at 100-105 degree range. Secondly, that you have airlocks in the system similarly causing reduced pressure and boiling at 105,

Also, does 105 degrees after shut-off seem a little high to anyone? I had a digital temp gauge on my car and the most it got to was 90-95 after shutoff... Though I did have a 52mm alloy radiator in it.

Cap is a brand new Nismo 1.3 bar item

Cooling system was flushed and checked by an RB26 expert. Absolutely no air locks near the head, Have also used the bleed screw ontop of the head myself. Brand new water pump was done 7.5K ago with timing belt etc.

Does not loose any coolant whatsoever. Overflow is marked at full when cold, all day everyday

Issue only shows itself when the turbos stop spinning and water pump is off. Can here coolant bubbling in top hose that connects to Thermo housing.

[jjman]

hmm, are you sure its not just fluid circulating? (this is normal) boiling is quite a noticeable sound and vibration but you may think the subtle sound of the fluid circulating is a mild boiling?

definitely shouldn't be boiling after shut off and also 105 degrees shouldn't be boiling if you have a 1.3bar cap....

[89CAL]

Is the nismo thermostat meant to compensate for the lower RPM downfalls of the N1 water pump? Ive never thought about this till now

Personally I would change away from the N1 water pump if it is mostly street driven but I understand if its an N1 GTR that might not be desirable

[djvoodoo]

hmm, are you sure its not just fluid circulating? (this is normal) boiling is quite a noticeable sound and vibration but you may think the subtle sound of the fluid circulating is a mild boiling?

definitely shouldn't be boiling after shut off and also 105 degrees shouldn't be boiling if you have a 1.3bar cap....

Top rad hose feels and sounds like a kettle boiling after 2 mins of engine shut off. The temp gauge on the MFD gets to about 105, and the temp gauge on the Power FC gets to 102 (middle of motor sensor??)

Engine has a top bill of health, nill oil leaks, nill water leaks

145-147 compression on all 6 cylinders (ODO 122,000k's)

[God_speed]

UPDATE on original post:

Just did 20 minute test run with a new radiator cap (HPI). No other changes so far (original t/stat still at this stage). Ambient temps in high 20s, flowing traffic. Took car through town then on M5, steady cruise, 110kmh.

Water temps did not exceed 75, with norm being low 70s. Much, much more within expected range. Returned home and put car in garage, idled, and temps slowly increased to 81-82. Turned A/C on, continued idling. Temps gradually increased to 87 max over the course of a few minutes. Seems much more normal now, no sudden / sharp increases in temp.

Next steps will be to take the car on a longer drive when I have time. And potentially have the system flushed again.

Charles and others - thanks again for your input, hopefully we've clinched it!

Below is a pic of the old genuine Nismo cap. It does indeed look as though it had been losing some pressure...

https://www.flickr.com/gp/21305018@N02/464t84

[niZmO_Man]

Should've taken a picture of the underside.

[God_speed]

Before I set it on fire:

Obviously, in hindsight, the underside didn't look too good.

The spring itself looked more or less fine, however.

[GTR_JOEY]

All I can say is be careful what pressure your cap you use. Yes a1.3 bar cap will raise your boiling point BUT it is more likely to spring a leak ie behind the water pump.

For street duties 1-1.1 is more then enough. I think standard is 0.9 bar

[God_speed]

Yeah, worthwhile mentioning mate.

Just can't believe a genuine Nismo item failed like that. That is, if the car continues to run well and confirms the cap as the problem.

[Gts-t]

Good to hear you got it sorted matt, the radiator cap is always the cheapest and easiest place to start especially given the symptoms you had, im not suprised the nismo one failed after all its not made to a higher quality level than the standard one it just holds more pressure.

In my opinion theres nothing wrong with running a 1.3bar cap even on a daily street car as it is only roughly 5 psi more pressure in the cooling system and unlikely to make the water pump leak prematurely. What does stuff the seal in the water pump is debris in the water from not maintaing it with regular coolant changes. Which leads me to my next point, that if the coolant is old/not maintained it loses its anti boil properties which will contribute to or cause irregular overheating just like a faulty radiator cap.

For those with boiling after you switch the car off thats all it can be, its either not bled properly, the radiator cap isnt holding pressure or your coolants anti boil properties are no longer there

Edited March 9, 2015 by Gts30t

[GTR_JOEY]

Unlikely may be the case.

Mine was fine, put a new radiator cap on... All of a sudden leaks, changed cap to 1 bar, no leaks

5psi doesn't sound much but it's over 30% more then standard

Just something to keep in the memory bank

[God_speed]

Thanks boys. Yeah I will keep an eye on it and hopefully that's hit the nail on the head. I guess they do fail with age. Not sure how old it was to be honest. Coolant was less than 1,000km old in my case, but yeah I understand there are plenty of Skylines running around with old coolant after importing from Japan. Should be one of the first things done to the car upon landing, along with a major service.