low temp thermostat

[sambb]

When I do my radiator, I'm going to fit the 82 degree (rather than 90 degree stock) thermostat. My question relates to the interplay of this thermostat with the fan switch. There is a 91/100 degree stock one and an aftermarket 85/90 degree one.
The guys at Awesome GTi said that on our Polo the fan control actually looks at the engine temp and the radiator temp as seen by the fan switch.
So to my mind if I change to the lower temp thermostat, I'd pretty much have to be running the lower temp radiator fan switch too wouldn't I so that the two marry up?
anyone gone down this path??

any advice welcome as I need to get onto ordering bits before my radiator has a haemorrhage

sam

[Eddy]

Hoyhoy.

Interesting subject Sam.

[louis19]

I believe Sean's car runs a 71C thermostat. Might be worth a chat with him or Gav as he might know a bit more info on the subject

[sambb]

Yeah I'm just not sure how it will play out if I run the cooler thermostat but retain the standard fan switch. Awesome thought that the ECU would probably prioritise the engine temp sensor reading and override the fan control even though the switch should theoretically only turn on at 100 degrees and back off at 91. I'd just hate for it to not work out that way and the fans end up hardly being on.
I was surprised that the our fan switch could input to the ECU but apparently its not a dumb/local switch like in the golf mk3/4 & bora. Actually after re reading their return email I'm going to have to get clarification on whether it may be more than just incompatible with the fan control system - I'll have to check if the 85/90 fan switch will even fit!

[Stuwey]

Why do you want it to run cooler?

[sambb]

Just got a return email from Awesome. He thought that running the one step cooler thermostat would be effective at keeping the engine temps more consistent with the standard fan switch retained. I'll have to clarify again but he seemed to intimate that doing the switch too might be a bridge too far and cause the ECU to enrichen the fuel trims.
All I want is to smooth out any big temp differentials between the engine and radiator and the existing thermostat doing big temp dumps in and out of the engine. The whole sequence of events at hilllclimbs absolutely cooks the engine - sitting in the line, launching hot and then having to shut it down hot with no cool down possible. I've learnt a few tricks like turning the A/C on to keep the radiator fans running which may help but I'm afraid I'm going to warp/blow something that I can't afford to fix. I'm not keen on any detrimental effects on trims though

[Martin]

I've never been keen on lower temp thermostats - the engine is designed to run at 90 degrees (tolerances and ECU)
(5 degrees lower is not a big deal but ~20 degrees is way too much, the ECU will notice that and intervene)

There should not be any big temperature differentials between the engine and radiator - no issue there

Certainly going hard on a low speed hill climb may not give enough airflow over the radiator,
what temp does the engine reach after the finish line?
As long as it's not over 100 you don't have a problem (imo)
Does idling for a few minutes (with the A/C on) not bring the temperature down?

Turning the A/C on will turn the A/C fan on which will give airflow over the radiator
It will also be robbing some power from the engine to drive the pump

This is a street car you use at hill climb events?

You can add manual circuitry to turn both the radiator and A/C fan on
(despite the ECU not turning the fan on and the A/C being off)
When turned off the ECU and A/C will be free to control the fans as per normal

A larger radiator (normally thicker) would be the next thing to look for

More shrouding around the radiator to block gaps will also help
Air always takes the path of least resistance - cool air will escape through gaps rather than go through the radiator

[Stuwey]

I think this is all a bit storm-in-a-teacup. Modern engines run at peak efficiency when hot. In the bad old days 82C was the aim - these days running at 95C+ isn't just not a problem, it's actually what they aim for.

Until it's boiling and expelling the coolant from the header tank, it's fine.

[sambb]

That's exactly it. Modern engines are designed to run hot (and lean) because hot lean engines produce the best fuel economy. Fuel efficiency not power efficiency is the aim of the game when they do that. If VAG engineers had designed our cars specifically for what we are doing to our cars and in our climate, I think its reasonable to assume they'd have slightly uprated the cooling spec. I don't see anything twisted about looking into the cooling system when a motor with 100hp more than stock, is being baked on and off the line for 2 days straight in Australian 36 degree heat, when it was designed for deutsch shopping malls.
Going to the lower thermostat is just going to mellow out the extremes so that engine temp won't cycle as much. Why have head temps in the high 90's and then climbing beyond that when you shut it down hot, and a radiator full of cool water that the thermostat won't let through. It'll be more steady state when being abused this way.
Remember we still have an iron block and alloy head. The turbo will heat its cooling water in an extreme way when shut off like this too- bolts stretch etc etc
At any rate Awesome gti just confirmed that the thermostat will do just that but won't drop temps to any degree where the ECU will assume a cold engine state and start to mangle fuel trims. They did confirm that the fan switch system should be left alone though.
I was going to do what Martin suggested and have a good look at the shrouding too.

[Eddy]

Hoyhoy.

I found if ya having a serious go @ the track the thermostat won't make too much difference because the temps are way up anyway.
I found that an extra oil cooler, water-meth & extra engine ventilation helped a lot.

[Martin]

Stock NA engines go ok at the track (unless it's a 40 deg day) - no water temperature problems
Turbo cars do rocket the oil temperature - but again, fine on the water temperature
I can well imagine hill climbs providing a unique challenge

[sambb]

hmm sounds like you guys think that oil temp might be the bigger issue. I can't remember seeing one anywhere when going through it, but is there a VCDS block that includes oil temp?

[seangti]

hmm sounds like you guys think that oil temp might be the bigger issue. I can't remember seeing one anywhere when going through it, but is there a VCDS block that includes oil temp?

I've never come across an oil temp sensor, I don't believe there is one on the 9n. I'd like to log oil temp and oil pressure but it doesn't come through the ECU. For a hill climb, I'd have thought the concerns would be the other way round, i.e. getting everything up to temp ASAP rather than cooling.

My car has a cooler thermostat, I can't recall what temp it is without looking at the build thread. I've had no overheating concerns and tracked in to mid to upper 30's, sometimes for some quite long sessions. It does bleed boost quite significantly when the temps get up, I was getting only 13psi boost the other weekend after a few laps whereas peak is 19psi. A less committed lap brought the boost back to 16-17psi. If I was to consider cooling (which I am), it'd be an oil cooler with thermostat. I feel with the greater amount of oil and the increased viscosity of oil over water it would have a greater influence on stabilizing temperatures.

I also need to better understand the boost drop in high ambient temps - but that's not this thread

[sambb]

I've only done a few hillclimbs where the car really cooked. They were king Edward park and panorama which were both 35+ degree days. Most other events are martialled differently but at these ones where the 'pits' are at the top, they would put you into a grid or reverse grid at the top where you wait till the class in front has all come up. They then pace car you down the hill where the field either u turns or reverses back into the correct running order behind the 'tyre warming area'. By the time 20 cars have launched and you've been creeping up bit by bit to get into the blocks (and on the way down you were accelerating and braking to get as much temperature into the brakes and rims which in turn heats the tyres from the inside out when your are sitting still later) the car is pretty much on max when you leave the line. When you finish the run you are basically straight into the pit area where you shut it down. I'd normally wait for the fans to stop before shutting it down but on these days they weren't going to. Yeah the electric water pump runs on after stoppage for a tiny bit, but by then has the thermostat already closed?? Maybe not if a lower temp thermostat is in there though. And when I went to restart the car for my next run (sometimes an hour later due to a crash or something) the fans would be on again almost immediately so it was cooking. I've not logged water temps when the car has been switched off for a while after a quick flogging but I can only imagine they get pretty dam high. It just seemed particularly hard on the car - everything your taught not to do eg idling a car to cool it, shutting it down hot. Just looking for some cheap insurance while I have the front of my car out.
But then again when I did Ringwood A3 once in sideways rain in winter the engine actually needed to be brought up to temp before each run and there you get much smaller fields that are martialled at the bottom of the hill too. I've always taken good care of my cars re warm up/down etc so yeah some events are fine, but other events make me wince a bit.
Re your boost, I've suffered from that too and I can honestly say that with the water injection running in real anger for the first time at Bathurst it was like driving the car on a cold night in comparison. It could be just your inlet temps. Or could the calculated EGT's be climbing and putting the ECU into a nanny mode?
Sean was your lower temp thermostat an ECS part or was it off another OE car that fits our housing. I'm going to pick VW parts' brain and see if any old bosch thermostat from repco etc will fit.

[sambb]

I just got off the phone to VW parts. The part they carry for our car is an 83/102 degree. My best guess is that this is what's referred to as the stock 90 degree thermostat by ECS. The ECS/neuspeed one is listed as 82 degree which probably means open 92/closed 72. If anyone can confirm that that's how they name the thermostats relative to their open/closed specs that'd be great.