Thermostats

[TokyoTaxi]

I recently put a 53mm Koyo radiator in a mates R34GTt for him and all is well, but it actually works SO well it has me wondering if there's a chance of thermal shock when winter sets in ?

I know that the RB25DET NEO has a thermostat that opens at 82 Deg C, so I could put a NISMO one in and drop that to 62 Deg C which would lessen the effect but would that in turn change the efficiency of the engine ? ( he uses it as a daily + occasional track day )

I could put an OEM Non-NEO one in but that would only drop the opening temp by 5.5 Deg C ( to 76.5 Deg C ) so I don't think that would help.

Or, am I just worrying about nothing ? ( He's spent a bit on his car so I'd hate to see him wind up with a cracked block etc )

Anyway, some opinions from those in the know would be greatly appreciated.

[Craved]

im a little confused as to your question.

But the thermostat controls the water LEAVING the engine, so this maintains via its flow control the temperature of the water inside the motor.

there is very little chance of a radiator that works too well damaging the motor whilst a correctly working thermostat is in place.

[TokyoTaxi]

OK, so yeah, the thermostat lets the hot water out of the engine & into the radiator right ? So by virtue of that, cool water must enter the engine from the radiator right ? If the engine is hot ( operating temp = 80 deg C in a NEO ) and the water re-entering the engine is "cold", could it cause thermal shock ?

The reason I posed this question is that when I fitted the Koyo and we went for a 15 min test drive, we pulled straight over and opened the bonnet and I felt the top tank and it was hot as you'd expect. I then touched the bottom tank and it was still cool. This got me thinking, if he went down to Wakefield for a track day during winter ( often gets below zero ), could the engine suffer thermal shock ?

If the answer is yes, would a NISMO thermostat be an acceptable option the reduce the difference between the engines operatng temp and the coolant temp in the radiator on say a 0 deg day ?

Then, would fitting the NISMO thermostat cause any operating issues ? ( keeping in mind that a NISMO thermostat opens at 20 deg C lower than the OEM NEO item ).

Hope that makes sense

[SteveL]

Or, am I just worrying about nothing ?

Yes, you are. As long as the thermostat is working correctly and the rest of the cooling system is in good nick there is no problem.

[SteveL]

But the thermostat controls the water LEAVING the engine, so this maintains via its flow control the temperature of the water inside the motor.

In RB engines (and, generally, all engines with a block mounted thermostat) the thermostat directly controls water flow into the block (the lower rad hose is for cooled water after it has been through the radiator). The thermostat senses water temp in the block and allows cool(er) water into the block as temp rises.

[Craved]

In RB engines (and, generally, all engines with a block mounted thermostat) the thermostat directly controls water flow into the block (the lower rad hose is for cooled water after it has been through the radiator). The thermostat senses water temp in the block and allows cool(er) water into the block as temp rises.

haha my bad, you're correct

[TokyoTaxi]

OK so lets run through how the cooling system works in a NEO RB25.

From cold, the engine warms up to operating temp ( rather quickly to ~80C ) and the coolant in the radiator is still at ~ ambient. There might be a tiny bit of coolant at operating temp that flows through the bleed hole in the thermostat but essentially, the engine temp is ~80C and the coolant in the radiator is ~ambient. Now, the thermostat starts to open and allow hot water out of the engine and into the radiator. By virtue of that action, the ~ambient temp coolant is moved from the radiator back into the engine through the bottom hose ( all good so far ? )

Now, if the engine's operating temp is ~80C and ambient should be below freezing, when the thermostat opens, the COLD coolant is now flowing back into the engine block which is ~80C. Only when the COLD coolant has passed through the engine ( absorbing heat along the way ) and reached the thermostat would the thermostat close ( still on track ? ). By this time, could the coolant have caused any thermal damage around the entry point in the block ?

After a small amount of research I found the following which seems to support my theory:

ARC FLOW CONTROL THERMOSTAT

This thermostat was produced for the purpose of preventing sudden coolant temperature change.

Three gaps on the newly invented valve control coolant flow properly.

SARD COOLING THERMO

Cooling Thermo prevents overheat and power down on high power engines by keeping coolant temperature around 68C. This thermostat has special flow control valve in it, and this valve prevents sudden temperature change of coolant, which might damage the engine or radiator.

Now I know that this situation ( driving around in below zero temps ) is not common, but my 1st question is, is thermal shock possible in this scenario with such an efficient radiator ? My second question is: If the answer to the first question is yes, and the fix is one of the above thermostats, would fitting one of these and effectively reducing the engine's operating temp by ~10C have any adverse effects on the engine's performance as controlled by the stock ECU ( which expects the engine to reach ~80C ) ? So to put it another way, will the ECU treat the engine as if it's still warming up and not at operating temp and run it rich ?

Sorry for the ultra long post but I hope that makes things clearer.

P.S. When I used to work on race cars, we never used to have a thermostat fitted. We used to run a restrictor in place of the thermostat and "part" of the reason was ( I was taught ) to prevent thermal shock when racing in cold climates.

[NickR33]

I have a Trust radiator and Nismo 62º thermostat in the GTR... I don't know if its helping prevent thermal shock but it makes it very hard to get heat into the motor on cold nights... for a car running the stock ecu as you say this will make it run rich (closed loop) until it gets up to temp

for a street car with standard ecu I would leave the thermostat OEM... how cold does it get up there in winter! you would never see 0º temps in Melbourne, even in the middle of winter unless your driving in the middle of the night you would be surprised to see much less than about 15º

I guess if you went to the track on a really cold day you could try and idle the car up to operating temp... with no airflow over the radiator and the heat from the engine warming it you would lessen the chance of thermal shock?

[blind_elk]

Maybe first point to be made - once the engine is at thermostatted temperature, the radiator will not cool the coolant to ambient temperatures, or to anything even approaching ambient.

Second point - if the coolant cools too much, the thermostat will close slightly, restricting the rate at which the cool(er) coolant can enter the block.

Third point - most thermostats have a small bleed hole in the flat part so that water can always circulate, even when the thermostat is closed.

We do get to 0 in Melbourne - not often, but there are the odd early mornings where ice can cover a car left outside overnight.

[**RB2530**]

If you are concerned about thermal shock in the block as the thermostat opens consider this...

1. The temperature of the water inside the radiator before the thermostat opens will be the same temp as the ambient air. This will be true no matter what size the radiator is and it will be independant of road speed...

2. Thermal shock will most be severe as soon as the cold water hits the hot internals of the block. What needs to be considered is change in block temp vs time. What governs this how quickly the thermostat opens. They normally open very slowly. They do not open instantaneously. It also depends a bit on the size of the water pump as this dictates water flow rate.

3. A bigger radiator will only change the steady state temp of the cooling system once the thermostat has opened. But the thermostat will start to close if the system temp gets to cool. The system then warms up opens up ts and so on...its a closed loop system so it controls it self.

So imo stick with the stock thermostat and the engine probably wont even know it has a bigger radiator on a 'cold day'.

[TokyoTaxi]

Thanks for all the input gent's ! I'm probably being a bit paranoid but don't want my mate to encounter any problems as a result of any work I've done for him.

Just to clarify a point, here in NSW the temps usually don't get super cold but when I used to do Wakefield Park track days myself, I used to drive down to the track from Syd early in the morning and would frequently encounter temps of -5DegC and when pulling up for petrol, would pull sheets of ice off the front bumper, so that's where I was coming from

Oh, and I just re-read the comment by SteveL. Is that correct ?? The water flows from the top tank, through the thermostat and into the block ?? For some strange reason I've got it embedded in my mind as the other way around.

P.S. In my car I'm actually thinking about fitting an OEM R33 RB25DET ( Non-NEO ) to drop the operating temp to 76.5C just to see what happens

[TokyoTaxi]

In RB engines (and, generally, all engines with a block mounted thermostat) the thermostat directly controls water flow into the block (the lower rad hose is for cooled water after it has been through the radiator). The thermostat senses water temp in the block and allows cool(er) water into the block as temp rises.

For the life of me, I can't see how the above can be true.

For the thermostat to work properly, the wax pellet end must be immersed in the water which controls it's function and that's in the block of an RB25. And if water flowed from the radiator into the engine via the thermostat, the cooler water flowing over the thermostat would cause the thermostat to close prematurely. Plus, the top tank is always hotter than the bottom one indicating that the engine's coolant is being evacuated from the block via the thermostat.

[lachlanw]

as in the thermo stat controls it by leting water out . if it cant get out then no more can get in can it

[lachlanw]

any of you ever consider how skylines got on in japan where its cold as some of the time ? or why they come with "ANTIFREEZE" in them

is this thread from the same guy that was worried about cracking the block by topping up his radiator overflow bottle with cold water when the engine was hot ?

the whole piont in a radiator is to supply cool water to the engine as the thermo stat allows . doesnt matter how cool

and the fact that the "cool" water in the bottom rad hose is in constant contact with the "hot" water inside the block

[Wacky Dee]

no it's not the same guy ..is that why you dug up a 6 month old thread?

Just for the record I think the Steve guy above has got it wrong completely in terms of which hoses is for what. But he's right in saying you are (were) worrying about nothing. The cooling system is pressurized and will only allow so much water IN as much as has come out through the thermostat. The radiator no matter how good will never make the water freezing cold, only a bit colder than what it was when it came out of the engine.

Other important points which were probably mentioned already .. the thermostat is not an on/off switch, it opens slowly from 82c to 95c on the NEO. Bigger radiator that cools the coolant much better will just result in the thermostat opening and closing more often, nothing else.