Rb26 Running Hot

[God_speed]

What could be causing an RB26's water temp to run steadily at 85-95 degrees C in normal road driving, then with no change in driving behaviour, suddenly increase more than 20 degrees in the space of less than 20 seconds, as recorded by the MFD?

Ambient temperature is approx 30 degrees. Temp will be at 95 at a steady cruise then increase to 119 then drop back to 95-100 just as quickly - all in less than a minute.

Cooling system has been bled (though could probably be bled even more?)

Nismo radiator

Coolant flush less than 2,000km ago

N1 water pump

Car has Nismo thermostat I believe, but not 100% sure.

[GTR_JOEY]

How long has this been happening?

Any modifications since before this problem began?

[Sinista32]

I am no mechanic - just old

85-95 sounds normal but does indicate it is not a Nismo thermostat which would be running cooler than 80.

The sudden increase and then just as sudden reduction I think could be Air or more likely a slipping belt on the water pump.

Another thought because I love to jump in without all the knowledge. Temp Sender on the housing or stuck thermostat.

Edited February 15, 2015 by Sinista32

[GTR_JOEY]

Yep 85 is fine, Around 95 is starting to get up there

Need to confirm that your water temp is actually getting that high and not the result of a bad sensor

[God_speed]

Thanks guys

I'm thinking thermostat to begin with. I will probably change it anyway for insurance or at least have it checked.

It's happened on a few occasions now, without even running the car hard. No major mods before the onset of this issue.

I just had to stop the engine in a turning lane as it just hit 120 and I switched her off immediately. Waited about 10 minutes but it wasn't decreasing in temperature by much if anything. Ran the blower on max heat. Managed to start it after waiting the 10 mins and the tune has a safety precaution programmed into the ECU, I believe. Ran like a dog and wouldn't rev, but I got enough revs out of it to get it moving and to get the heater running and circulating the coolant. As soon as it got moving and I managed to put some proper revs on the motor (say 3k), the water temp plummeted back to 100-105. I'm sitting in a bloody servo atm.

How is it possible for the temperature to fluctuate so dramatically within such a short space of time (mere seconds) if the system is still sealed, unless it is a temp sensor, or there is a shitload of air in the system?

I just bled the motor last weekend via the screw with the car sitting on a mild incline.

[GTRPSI]

Sounds like a sticking thermo, its the first thing to try.

[Duncan]

yep and turf the nismo thermostat and put a standard one back in, unless you are racing it. also, don't bother with an n1 pump on a road car it just gives you less water flow at road speeds.

[Ben C34]

I would be checking that the coolant has been bled correctly.

[God_speed]

Thanks boys. I believe first step is to source a replacement BNR34 t/stat and get coolant bled properly after fitting. It's obviously a regular one currently, as some of you have stated the car clearly operates at over 80C.

Duncan, N1 water pump is factory for this particular motor in question. I do understand it has fewer (but larger) blades to the impeller, thus requiring more RPM to operate at maximum efficiency.

[Wongy]

I've been having this problem lately as well, i'm running NISMO thermostat and stock water pump i believe, but my temps haven't reached up to 100+ like Mat has, mine seems to reach max 95-98 on a hot day around 37-38 degrees, it only tends to climb up slowly above 90 when i'm stopped at lights, but when i'm constantly moving it slowly starts to decline below 90 to around 85-86, not sure what the issue is, might need to bleed coolant and see what happens =\ and my air con seems to get warm when i'm stopped at lights after my car has been in the hot sun for awile, but that might be totally unrelated to high water temp and might just be my ac gas xD

[Sinista32]

Hi Nathan - I wouldn't say your temp is an issue at all. Stopped at lights - temp raising is normal.

BTW - are you running a larger radiator at all ? If you are that's good for it too.

With the AC have you had/done the mod to make sure your fan is always on when AC is on ?

There is a tutorial on it in the DIY's.

If you haven't had your AC serviced since ownership I would do it anyway.

[Duncan]

ahh yes. still, n1 pump is not an improvement on a street car.

unless you've changed something recently a bleeding problem is unlikely, a pressure test of the system might be worthwhile to see if you have a small leak

Nathan don't worry in the slightest about temps near 100. Check the stock gauge when it's at 100 you'll see its still in the middle, nowhere near hot....having a digital temp gauge can just give you unnecessary worries

[God_speed]

Thanks Dunc.

Can anyone confirm if the stock Nissan BNR34 thermostat part # is 2120042L05?

http://nissan.epc-data.com/skyline/bnr34/3956-rb26dett/engine/210/21200/

[Wongy]

Hi Nathan - I wouldn't say your temp is an issue at all. Stopped at lights - temp raising is normal.

BTW - are you running a larger radiator at all ? If you are that's good for it too.

With the AC have you had/done the mod to make sure your fan is always on when AC is on ?

There is a tutorial on it in the DIY's.

If you haven't had your AC serviced since ownership I would do it anyway.

Yea, read that DIY but i'm gonna have to read it a few more times till i get confident enough to do it haha. and as far as i know its a stock radiator still, still has the nissan stickers on it, and yea, have to get the ac gas checked, flushed if need be and put new gas in.

Thanks for your help.

ahh yes. still, n1 pump is not an improvement on a street car.

unless you've changed something recently a bleeding problem is unlikely, a pressure test of the system might be worthwhile to see if you have a small leak

Nathan don't worry in the slightest about temps near 100. Check the stock gauge when it's at 100 you'll see its still in the middle, nowhere near hot....having a digital temp gauge can just give you unnecessary worries

On the cluster the needle slightly goes over the middle line =\ so not sure if thats still considered normal, i thought normal was never over the halfway line haha, but i guess if you say its nothing to worry about then i shouldn't worry haha, but i'm going to do a coolant flush anyway since it hasn't been done since i've bought the car.

Thanks for your help.

[Gts-t]

Lots of good ideas but the first thing to check especially given your symptoms is if the radiator cap actually holding pressure. Run your car up to operating temp and squeeze the top hose, you should feel a decent amount of pressure in there. If it's a fairly new radiator cap it's probably not going to be your problem.

Never hurts to do a new thermostat, coolant, bleed and pressure test just to eliminate any of those concerns, I doubt it's a blocked radiator given it's a nismo but it could happen. Another issue can be corroded or missing blades on the water pump which I've seen before

[God_speed]

Thanks Mick. It's a Nismo rad cap; no fluid leaking from around the cap area, but I suppose you're saying it could be letting too much into the overflow tank, is that right?

[Sinista32]

Standard GTR radiator cap is 0.9 and the Nismo is 1.3.

Meaning more pressure (heat) is required for the cap to open and the pressure/water to travel to the overflow, cool and return.

Edit. BTW GTS30t is correct ^. Is a good place to start

Edited February 17, 2015 by Sinista32

[Gts-t]

It's always a good idea in any car to pop your hood once a week and make sure the coolant level in the overflow bottle remains at the same level. If it's not then there will be an issue somewhere,

My point regarding the radiator cap is one I've seen quite a few times when a cooling system becomes marginal or is ok most days but gets too hot now and then. A worn water pump impellor (blades) could also cause the system to be marginal some days as could a slipping belt. I haven't seen a worn water pump belt cause such issues but it definitely could if it was slipping at times. as long as the belt is there and is in good condition and is correctly tensioned (too loose could be slipping) it should be working fine, an over tensioned belt is likely to wear the bearing in the water pump out faster but that shouldn't be part of your issue.

The cooling system is under pressure because it raises the boiling point of the fluid. This is good for a number or reasons I won't bother going into now, For example under zero pressure water boils are 100 deg Celsius. Under 30kpa of pressure it is about 108 deg boiling point and 90kpa is about 130 degrees. You do not want the water/coolant boiling in any engine regardless of how hot it has been designed to run.

Given the radiator cap is nismo and the radiator is nismo they should be fairly new and working fine (ie holding pressure and the radiator not blocked) How old is the water pump?

I'd like you to have a look at the water level in the overflow bottle fill it to the max mark when it is cold ( ie first thing in the morning) top up with water or demineralised water if fussy and then check after you drive it every time once it has cooled down for say a week. Particularly if it the temp has gone above 100 in normal driving and then report back.

If the level in the overflow bottle is staying the same we can eliminate a few things and go from there.

After thinking about this for awhile I'm looking to lean towards a sticking thermostat given how fast you said the temps can rise and then drop back down. As well as sticking it may not be fully opening.

[God_speed]

Cheers Mick. All makes sense and fits well with what I did know. Thanks for such a well written and detailed explanation.

I've actually gone ahead and ordered a replacement OEM thermostat (just a regular BNR34 one, not a Nismo) and will have it fitted as soon as it gets here.

In terms of the water level, from memory I've hardly ever had to add any coolant to either radiator or overflow, and the overflow is usually at the Max mark when cold. But I'll keep an eye on this and report back if the level fluctuates or if it remains consistent. The car is rarely driven (around once a week) so it makes monitoring a bit less practical, but I'll look into it anyway.

The (N1) water pump is original, I believe. The vehicle's only travelled 43,000 km and was in Australia since new (2002).

[Gts-t]

Not a problem Matt, that is good news the water level in the overflow stays at the same level and it is not using and or leaking any water, or pushing any out of the overflow bottle.

As it has gotten hot before and no doubt will do it again, it is good that you have ordered a thermostat (standard is ideal I think, but I have no experience racing with a nismo low temp one) to atleast eliminate that straight away. For the sake of a few bucks I'd still get new coolant fitted making sure it's bled correctly, and pressure test the system. Also ask the mechanic to check that the radiator cap is actually holding pressure. It's an easy check you could do youself if you wanted though like I said just by squeezing the radiator top hose once your car is up to operating temp. It should be quite firm, not soft like if you squeezed it first thing I the morning when the car is cool.

With that amount of kms I would be surprised I'd the water pump blades would be corroded especially if it's always had good quality coolant fitted but stranger things probaby have happened and may be worth investigating as a last resort if everything else fails as time can be just as much a factor as km's sometimes,

I have zero experience with the n1 water pump (moving less fluid at low speeds) but I don't think even and n1 should be making your temps get that high.

Good luck with it