Mark944na86

OK, I can see the potential problem: The standard thermostat is rated to open at about the same temp the the fans cut out with the cooler switch (85C). This means that potentially the radiator could be too cool to allow the thermostat to open fully, even after the engine has reached normal operating temp.

Given the hassle involved in changing the thermostat (snap ring etc.), I'd probably be inclined just to get the normal temp range switch and be done with it. However, the local parts supplier only has the lower range switch in stock (grrr...).

Anyone actually tried to run a lower temp switch with a normal temp thermostat? Were there really practical problems (overheating, etc), or are the problems more of an "in principle" nature?

Basically, I suppose I have to decide whether to wait for the normal temp range switch to become available. In the meantime, I'm pulling fuses when the ignition is off; tedious, but at least it stops the battery going flat!

BTW, Mike C., I'm enjoying Brisbane very much, except perhaps in the hottest parts of summer. It's not just the 944s that feel the heat around here!

-Mark

hosrom_951

I have with my 88 NA, gauge read solid at midway (just over 2nd mark ~85-90C) with AC on full and 110+F weather.

Mark944na86

So you didn't bother to change your thermostat to a lower temp one? Why didn't you? Too much hassle?

BTW, from what I can gather, running with aircon on makes the temp settings of the thermo fan switch irrelevant anyway, since the relay is wired to have the fans on all the time whenever the AC is switch on.

-Mark

hosrom_951

I did not change the thermostat because the dealer did not hav one in stock, but the high speed fans stopped working, and i replaced the switch with the cooler one.

One year later, the thermostat was stuck on full closed, the car over heated and then i replaced it with a cooler one.

Mark944na86

So did the car run normally during that year? Do you feel the eventual thermostat failure was contributed to in any way by running with the lower temp fan switch?

If the car will run without issues with the cooler fan switch and the normal thermostat, I'll probably just try that combination out in the first instance.

BTW, the part no for the S2 thermostat is rated to open at 83C, but it's not clear what the tolerances are, and at what temp it starts to open, and what temp it is fully open. If fully open at 83C, then there should be no problem. If it is only partly open at 85C, then I could imagine there could be issues...

Unfortunately, no easy way to test I can see (given that anything "easy" would by definition not involve removing the thermostat form the car.)

-Mark

GlenL

A bit late but let me get into this...

The way these work is that the thermostat controls the operating temperature of the engine by opening when it gets up to operating temp while the fan switch turns on if the radiator isn't cooling enough. By having pairs of components the engineers have set it up so the water coming into the engine will be 10C cooler than the water leaving the engine.

The goal of the two components is to have the engine operate at the correct temperature. Cooler is not necessarily better. As the stock thermostat is the hot one (93C? Ain't finding the numbers) most people can go with the higher-temp radiator fan switch.

The reason to go with the cooler values is that the car is operated in warmer climate. This allows the engine to cool more when shut off. Presumably it was running hotter and the extra battery drain is worth it.

What you don't want is to use a low-temp fan switch with a high-temp thermostat. This will have a big spread between incoming and outgoing water temps. Will it thermally stress the aluminum components? Well it can't help. Will it make the thermostat cycle more in operation and cause a failure? Well it can't make it last longer.

Getting the dash gauge to run a bit lower always sounds good. If the car runs at the correct temp it's not any sort of improvement. If the car is truely running hot it's not going to be due to the fan not coming on soon enough. That's masking the symptoms instead of solving the problem.

I will grant that if the radiator is clogged and not flowing well then getting cooler water out will be a good thing. This will only work until it ambient conditions get hot or the car is driven hard. Or both.

Guess that's a lengthy rant. People want cooler running cars in general but most don't need that. If you're in, say, the Middle East or hot parts of Austrailia, then it's a different issue. For youse guys the extra cool-down is worth the battery drain and shorter fan life.

hosrom_951

The thermostat failed on my car because it was the original from factory and never replaced since 1988, i do not beleive to have been effected by the lower switch.

AR10

GlenL RIGHT ON!

Mark944na86

Thanks Hussam.

GlenL, stock thermostat on an S2 is 83C, and the stock thermo fan switch is 95-102C.

I've just replaced my thermo switch with the lower temp 85-95C version. Thermostat is stock (as far as I know).

So the fans are going to be working harder. Basically, extra airflow. But I can't see how this in itself will create problems... otherwise you'd get problems whenever you're cruising in cooler weather, and the natural airflow cools the radiator to 85C (or less, for that matter).

There was the point of the fans wearing out more quickly, which is a fair point. There was also the suggestion that the thermos fan switch cut-off at 85C might interfere with the thermostat opening fully, since the critical temps are so close (83C and 85C), but as long as the thermostat _is_ opening up, I just can't see 85C radiator coolant temps being a big problem in itself.

Perhaps if you could explain why having the thermo fan switch cool the radiator down a bit more is going to be different from driving down the highway on a cool day, I'd understand your point a bit more clearly. If changing over the thermostat was a trvial job, I'd probably just do it to be done with it, but since it's not, I'd like to understand exactly what the issue is before I undertake this (or merely find a different parts supplier to source a stock temp thermo fan switch.)

Cheers,

-Mark

Kokopelli

As far as I know my new radiator has the cooler fan switch. The temperature guage now sits on the first mark during driving and doesn't go higher than half way up, when stopped. Before the new radiator it used to bounce off the second white mark. The only thing I've noticed is that I now have condensation in the oil filler neck, which I didn't have before.

Mark944na86

This is a bit of a worry... I know one thing the oil temps have to do is get high enough to boil any water out of the oil in order for the oil to manitain its lubrication properties... I don't know if this could be an indication the oil temps aren't getting hot enough during normal driving.

-Mark

Z-man

While I cannot dispute your claims, in a practical world, I cannot afford to run an engine at is most effecient temp range. Otherwise, I'd be buying a new motor every month!

I'd rather run cooler and give my motor longevity vs running too hot.

Yes, I do have the lower thermo and fan switches.

-Z.

AR10

I repeat; if the coolant is not boiling the engine is not overheating.

Z-man

However, a cooler engine has less of a chance of blowing up.

Now I'm not a betting man, but I'd much rather run my motor at cooler operating temps that higher ones.

Oh, BTW: all the lower thermo and switch do is allow the coolant to circulate a little sooner. For track applications, it's really moot, since you're past either temp range (Cooler or normal thermo) after about the first lap...

-Z.

Oddjob

The reality is that the lower temp fan switch really doesnt do much, and is absolutely fine to use with either the normal or low temp thermostat.

The fans only serve much purpose when the car is stationary, in stop and go traffic, driving below 15-20mph. Any speeds above that, and the majority of the air passing over the radiator is from the airstream, not what the fans are pulling through.

If for some reason, you do a lot of daily driving in stop and go traffic in a hot climate, and your car tends to overheat at a stand still, but cools fine when moving, you may want to consider using a lower temp fan switch, but chances are, it wont change things much/any.

As someone mentioned above, if you have the AC on, the fans run immediately and all the time to pull air across the AC condenser. It doesnt hurt the engine or adversely affect the cooling system to have the fans running more often or longer.

It wont change the operating temp range of the engine, the thermostat does that. I would be more concerned about running a lower temp thermostat in colder climates, but would not think twice about installing a low temp fan switch (if that was the only one readily available when I needed one).

As far as the engine running best right up until it seizes up...? The designers will have spec'd and built the engine with a specific operating temp range in mind. So all the component tolerances are set considering the different thermal expansion characteristics of the different materials. If the engine is run hotter than designed, its pretty typical that the moving components will start to tighten up, increasing friction (which reduces output power), and creating even more heat.

It does depend on the engine and the materials; a cast iron V8 with iron internals, will not behave the same as an Alusil block with alum pistons, steel rings, steel crank when over heated. Also, Im sure that a Porsche engine is built with tighter tolerances than a small block V8 - so I would be more concerned about overheating a 944 than a Nova.

Aluminum expands nearly 1 1/2 to 2 times as much as steel/iron per degree (depending on alloy composition). So think of what is happening to the head studs and head gasket if the block and head are expanding at almost twice the rate of the head studs - not much question as to why you see a lot of head gasket failures and warped heads, even broken studs on cars that have overheated.