Fender Thermostat Failure... With Science

[911SauCy]

Brain trust, I am coming to you with as much information as possible for your opinion. The old Sauce would have provided much less, so hopefully what I have gathered is sufficient to aid in a final determination. I believe the external T-Stat is shot on my '78 Targa...it is original to the car as far as I can tell from the history of receipts I have as well as me knowing I've not replaced in my 12yr owner ship...

Here goes: Car runs amazing, has a euro 3.0 (less than 10k miles on case-split rebuild, makes a ton of power, uses .5Q of oil in 3k mi) and Carrera front fender cooler. That said, Over the last season I've noticed it comes up to "temp" much sooner than in the past so I started digging.

I verified that the oil temp sensor and gauge in the car have corresponding numbers, and below is pic of temp in car when "hot"... First temp reading taken at motor was at the temp sensor, that showed 184F, which correctly correlates to what gauge shows:


Additional temps taken at the same time when car was running and "hot" or at operating temp show above:
The below all in the RR fender:
Oil Line from engine to external tstat housing: 207F
Oil return line from tstat housing back to tank: 126F
Oil line from tstat housing up to front cooler: 154
Oil return line from front cooler: 139

The below in FR Fender:
Oil line to cooler: 103F
Oil Return: 100F
Cooler itself: 84F

Ambient: 68F

I am thinking I will be pulling the oil lines, cooler, and tstat housing to clean and rebuild.

What are the opinions here?

Lastly, it's apparent the motor is basically only being cooled by the engine oil cooler and using the bypass in the loop to do so... I'm astonished that temps never really get above the 9 O'Clock or 200-210F mark given that...

[dannobee]

Before you do all that, take the thermostat element itself out and put it in some boiling water to see if it opens. It should open at 180 deg F or so (83 C). It's under the big cap with the screwdriver slot.

[David Inc.]

Definitely low or no flow situation. Do the lines going up front pass a visual inspection for crush damage? That will have a huge impact regardless of what your t-stat is doing.

And it's doing okay now but once summer comes and you have a spirited drive that motor is going to overwhelm the engine oil cooler in no time.

[grb008]

Was the car running with that low pressure, or was it just in ACC on the ignition?

[911SauCy]

It was running that pressure at idle at 184F, 750rpm. PSI along the rev range is spot on.

[911SauCy]

Dannobee…. I hear that, but… have you ever attempted that?! Nearly impossible, maybe if I had the caps with hex nut.

David Inc, no dents.

[brighton911]

My case was different but may be of interest. My car was very slow to warm up, and during colder weather, never got close to normal operating temps. So I pulled and tested the engine thermostat. Right on Q, the thermostat would open at the specified temp so I put it back in. No change. Not one to spend money needlessly yet knowing despite the evidence the that showed the thermostat OK, I replaced it. Now it warms up quickly and stays right on the first mark even through a considerable ambient temperature range. Doesn't make sense but that was my finding.

[911SauCy]

Originally Posted by brighton911

My case was different but may be of interest. My car was very slow to warm up, and during colder weather, never got close to normal operating temps. So I pulled and tested the engine thermostat. Right on Q, the thermostat would open at the specified temp so I put it back in. No change. Not one to spend money needlessly yet knowing despite the evidence the that showed the thermostat OK, I replaced it. Now it warms up quickly and stays right on the first mark even through a considerable ambient temperature range. Doesn't make sense but that was my finding.

That’s definitely strange…