Low oil temperature

[clesch]

I’m happy owner of a new to me, unrestored 1970S. I’ve just finished the paperwork, registered the car and went for my first drive (after the test drive) with it.

The car drives beautifully, PO claimed to have the engine rebuilt some 10000km ago but I don’t know what kind of rebuild it was since the throttle bodies and linkage seem to have 2mm play per ball cup.

The oil pressure acceptable (maybe even good?), around 4.5 bar at 3.500+ RPM, no blue smoke after cold starts. Since the car has over 150k documented kilometers on it, so I do believe that the engine was rebuilt in some way at some point.

What strikes me as odd is that I can’t seem to get the oil up to temperature. I just went for a 50 km drive in fair 20°C/70°F weather, up and down a few hills and some city driving:



I’m hesitant to rev the engine past 5000 rpm or drive the car hard since I'm not all that familiar with it yet and don’t want to blow anything up.

My first suspicion was that the oil thermostat is stuck in the open position, but that doesn’t seem to be the case as the oil lines and fittings in the front fender are absolutely cool to the touch.

A seasoned local Porsche mechanic test-drove the car with me (a lot harder than I ever have...) and thought that the engine runs perfectly fine. Temp was around 80°C/176°F when he was done, but I forgot to check the front fender to see if the thermostat opened.

Does this seem normal?

I read somewhere on this forum that many people don’t consider the engine warm enough for full throttle/revs until 80°C/176°F.
My oil would never reach this temperature without full throttle, seems like a catch 22 situation to me.

[mikael]

I had this behaviour on my 72E. It was the internal thermostat (as opposed to the external thermostat for the fender mounted cooler) that was stuck open. With a functioning thermostat it get's up to temperature much faster and then stay stable around 90 degrees.

You can slso check the oil temp sender to make sure that it's not a false reading.

[clesch]

I had this behaviour on my 72E. It was the internal thermostat (as opposed to the external thermostat for the fender mounted cooler) that was stuck open. With a functioning thermostat it get's up to temperature much faster and then stay stable around 90 degrees.

You can slso check the oil temp sender to make sure that it's not a false reading.

Thanks, I added this to the list of things to check.

1. Oil Sender Temperature (unlikely since the front cooler loop never opens, unless that thermostat is also malfunctioning)
2. Internal oil thermostat (seems the most likely to me at this point)
3. Fan pulley size (unlikely to have such a huge effect, and a quick check showed around 115mm for the fan-side pulley)

By the way, I can see my oil thermostat back there and noticed a threaded stud on top of it. Does that mean the thermostat is adjustable?

[edmayo]

Yes, your thermostat is adjustable. First I'd try a infra red temperature gun that you can aim at the temp sender area of the case and see if the gun reading corresponds to your gauge reading. If it does and the possibility exists that the ENGINE oil thermostat is stuck open, you can remove thermostat, put it and thermometer in a pan of water and heat up. The thermostat should start to open at about 190 degrees. If it is opening too soon you might be able to effect an adjustment with that screw on top. If none of that works you can buy just the insert and replace it, but you'll find the top of the thermostat is shorter than the original so you'll need to turn the adjustment screw most of the way in to touch the insert. Repeat test in water to verify opening setting.

[Flieger]

He means 190 degrees Fahrenheit of course.

[clesch]

Yes, your thermostat is adjustable. First I'd try a infra red temperature gun that you can aim at the temp sender area of the case and see if the gun reading corresponds to your gauge reading. If it does and the possibility exists that the ENGINE oil thermostat is stuck open, you can remove thermostat, put it and thermometer in a pan of water and heat up. The thermostat should start to open at about 190 degrees. If it is opening too soon you might be able to effect an adjustment with that screw on top. If none of that works you can buy just the insert and replace it, but you'll find the top of the thermostat is shorter than the original so you'll need to turn the adjustment screw most of the way in to touch the insert. Repeat test in water to verify opening setting.

The general area around the oil temperature sender seems to be close enough to what the gauge shows. I tried to get the thermostat out yesterday. The two screw nuts came out no problem, but I wasn’t able to dislodge the thermostat so I screwed them back on because I don’t want to damage anything. Waiting for my mechanic to come back from his holidays.

I drove another 15 km today hoping it would heat up in todays 36°C/100°F heat, but the gauge never went over 70°C/150°F. I did notice that the internal oil cooler (behind the passenger side rear wheel) is very warm to the touch, which to me is another indicator that the internal t-stat is stuck open.

He means 190 degrees Fahrenheit of course.

Yup, I figured that. Heating a pan of water to 190°C would be… difficult.

Thanks for your advice everyone, i appreciate it.

[edmayo]

I use a small crow foot pry bar to lift up the thermostat, the lip of the small bar will just fit under the gap.

Yours is a good problem to have,,,,most complaints are for too hot! Depending on how hard you pushed it in the 100 degree heat, only 150 for a 15KM (what, 8 miles?) is somewhat normal. I just happened to drive my 72S today, 104 temp, about 5 miles, driving the 45MPH speed limit, and it also got to about 150, sure wasn't 180. I was thinking of your question so I made a point to check the gauge.

[72targa]

Just a question for the experts...any chance the gauge needs to be calibrated?

[edmayo]

Peter, I think back in post #6 he mentioned that his infra red heat gun showed about the same temperature in the sender area as his gauge was showing. Reread that and make sure I didn't misunderstand.

[72targa]

Missed that! Still seems odd that the cooling is TOO efficient...