Mark Thornton

Well guys i have been driving my 928 5 Speed and it is fantastic to drive.. However I am a little concerned about my Engine temperature , it go's up to just under the 3/4 mark on the gauge . I haven't cked if the gauge is accurate but. I am concerned about summer driving..

worf928

195 degrees Fahrenheit as measured by the TEMP-II sensor.

It shouldn't get any hotter than that unless you're in 100-degree weather with the AC running.

On the highway on a cold day it may not get above 175.

dr bob

^^^ What Dave said. The thermostat is a very simple analog device. It uses expanding wax to move a piston that operates the rear gate, sending coolant flow to the radiator and/or recirculating it through the block based in incoming fluid temperature. The available hysteresis in the thermostat is somewhere around 10-15 degrees, so you'd see that kind of variation depending on total heat input minus total heat dissipated. Once the thermostat is all the way "open" to the radiator and "closed" to recirculation, temperature readings will directly reflect that heat balance. That changes depending on engine load and ambient conditions, with a multiplier on the "shedding" side that is related to transfer efficiency in the radiator. Radiator fouling internally, airflow blockage externally, plus some other related factors, ultimately define how high the coolant temp will go after the thermostat is at full travel position hot.


Mre than you wanted to know? I'm modeling heat exchanger efficiency right now for a new-to-me power plant steam generator. It's running on the other computers while I take a breath.

Wisconsin Joe

What neither of the two really smart guys mentioned clearly is that the gauge is notoriously unreliable. No two seem to read the same (slight exaggeration).

Get an IR temp gun, and shoot the temps under the hood (that's what Worf928 meant with measuring at the temp II).

worf928

I was not at a keyboard. And I figured that that didn't need sayin'.

But, since you opened the worm can and I'm now at a keyboard...

I find that the gauges 89.5+ that are marked with temperatures are more-often accurate that those prior. With the exception of GTS gauges that for some reason seem to be way off or just plain erratic more often than not.

In the former case the contacts are unprotected and often green with corrosion. By mid-'89 (perhaps all of '89) the gauge sender uses the same 2-pin AMP/Junior Time connector as the TEMP-II (with a rubber gasket.)

Don't ask me why GTSs gauges are wacky. No idea. Just data from a small sample set of rarely-driven garage queens.

OP didn't specify model year thus no way to know what I might write about the gauge.

Actually, the way I do it is with a contact thermometer on the base of the NTSC/TEMP-II sensor. I've found that shooting bits of the engine with an IR gun has a lot of variability and that you can have a spread of temps across the water bridge.

Bertrand Daoust

+1.

While we speak about the thermostat, I have a question.

Does a colder thermostat would make the car run richer?
Or richer for a longer period of time at start up only?

Just curious as "I think" my car runs richer since I put 75° thermostat.
But I'm really not sure.
Just asking.

Thanks.

worf928

If nothing else is wrong... then no.

Cold-start enrichment stops well below 175 (I don't remember exact temp, maybe 100F? (Have to look at Sharktuner maps)) for LH 2.3.

A colder thermostat will have zero effect on steady-state operating temperature on a 928: once the thermostat is open it is open. It can't get more open. It just gets to full open at a lower temperature. (See DrB's summary of balance above.)

If the TEMP-II is flaky, then yes, a colder thermostat might trick the LH into cold enrichment longer.

Bertrand Daoust

Ok. Got it.
Thanks Dave.

My TEMP-II is new (and tested good) so everything should be good on this side.
The LH has never been touched so... ?

But "if" it is running richer, quite sure it is not by much.

davek9

I'd like to add that the OP doesn't state what year his car is.

It's been my observation over the years that the S4's tend to read 1/2 to 3/4 of the temp gauge when up to temp and the 86 and earlier cars about 1/4 to 1/2 and can get to 3/4 with a high heat conditions.

Wisconsin Joe

For the record, my "really smart guys" comment was sincere. DrBob & Worf928 are 2 of the people on here whose advice I really listen to.

And I've learned (the hard way) when something "goes without saying", it's usually best to say it. Obvious stuff like inaccurate temp gauges, disconnecting the battery before doing any work, letting the front end settle after lifting the car, all that stuff that is obvious to us may or may not be obvious to everyone.

FredR

Bertrand,

Unless you have a really good reason to use it I would dump the 75C thermostat just as soon as you can. My experience with them is that it stuffs the fan temperature programme up a bit for starters.

Porsche designed these motors to run at a specific temperature range and opening the thermostat early only ensures it takes longer for the motor to fully warm. Indeed in a cooler climate where there is plenty of excess cooling capacity on a cold day the motor may not fully warm with whatever consequences that may have. On the flip side if it is a really hot day the motor is not going to run any cooler because of the 75C thermostat.

Regarding your question about enrichment I seem to remember there is a final small correction of plus 3 on the warm up map at 80C if my memory serves me correctly- this makes sense considering the stock thermostat is set to open at 83C. Thus if my memory is correct there will be a slightly larger correction for warm up at 76C which will not amount to much. If the applied correction factor were say 5 units this would represent 1% extra fuel [I think].

Both my 928's [90S4 then the 92 GTS] seemed to read identically in that the normal operating temperature sits just to the left of the last white line and when worked during our hot summer a bit above the last white line but note I have a bigger radiator, run a 30% glycol mix and run Redline water wetter. The stock radiator with a stock coolant would run close to the redline on my S4.

One thing to remember about the temp indicator used in the 928's I have owned is that there seems to be more proportionality in the reading than most cars exhibit. Other cars seem to warm up and miraculously the position of the needle never seems to change. I have a feeling this is an "industry con" to fool the driver into not complaining about seeing small movements on the gauge. The 928 gauge has clearly discernible resolution as one might expect to see. This may explain some of the reported nuances as when migrating to a 928 the new owner sees something not commonly seen on other cars.

In the case of the S4 and later models the real time to worry is when the high temperature alarm comes on and the only times I have seen this was on both occasions that my water pump impeller let go from the drive shaft and then I stopped the motor and let it cool off before before trying to limp home which in the summer months is a long time! fortunately I was close to home both times this happened some 12 years apart.

Regards

Fred

dr bob

Very true on the "other cars" thought. My Honda Pilot DD temp gauge makes it up to 'normal' position, than parks there regardless of actual coolant temp so long as it's within the normal operating range. With the datalogger plugged in, the coolant temp varies between about 175ºF and 220ºF on a summer day in traffic, with no gauge movement at all from it's "normal" position.

A couple decades ago I had a Ford Explorer SUV with an oil pressure gauge. Cold or hot, the gauge sat at the same postion when the engine was running. Then one day, on hot day, driving through the central valley of California and headed towards the Grapevine hill where cooling systems are tested to the extreme... The oil pressure gauge started to droop. (!!!!). Immediately pulled off the road with engine off, let it cool enought to check oil level. Level was fine. Restart the engine, gauge moves to lower powition and parks here. No noises, temp was OK, so motored on gently up the hill and home. Checked oil pressure with a manual gauge, and all was well. Tested the sender, which showed open-circuit with engine off, closed circuit (to my multimemeter) with engine running. Hmmm. Changed meter range and saw resistance, same with engine cold or warmed up. Found out that the "pressure sender" is just a switch, and the cluster has a resistor to put the gauge at 2/3 whenever the switch is closed. Out came the cluster to jumper the resistor, and a true pressure sender went in. I guess Ford didn't want to filed questions or warranty claims for oil pressure variations. So an "idiot gauge", but no "idiot light" to go with it; barely better than nothing at all.

mark kibort

i always advise feeling the radiator ..if its cooler near the bottom vs top, then you could have a radiator issue or stuck t-stat. when that seal goes up top near tstat on the block, it doesnt cool as well . Plus, air in lines can cause bad flow. (see burping system).

temp on temp gauge should be mid line , and creep up if fans are not doing their job.

usually, the gauge is pretty good. people always blame gauages, but usually there is another problem.

FredR

Bob,

We had a similar issue with my wife's old Mitsubishi Pajero 4x4 [Montero in the States]. This was the family car and one evening we went to pick my daughter up from her friend's house. The car suddenly felt warm and it was the a/c that had cut out- immediately glanced down at the temperature gauge and for the first time in some 15 years it moved up from the normal position but no where near the indicated red line. Like a chump I believed it and a few km later had to coast into a gas station and abandon the thing. The needle normally sat at about 1/3rd of the scale range, that evening it moved to about 2/3rd of scale and the red line was at full scale. The damm thing never made it to full scale. The water pump had failed, the system could not hold pressure and the temperature it measured was the boiling point of the coolant and thus the scale was inappropriate. Similar problem with my daughter's Kia Sorento- if that thing loses pressure it overheats in no time, no warning or alarm and first thing you know is you have warped heads.

You get what you pay for!

Rgds

Fred

WallyP

Another point to ponder is that the temp gauge doesn't work well at all with air in the system instead of coolant. I've had that situation twice - the Suburban survived it, the Trooper didn't...