Front Center Oil Cooler is keeping my temps too low

[11BC2]

Originally Posted by Bill Verburg

Just partially cover the cooler

That is exactly what Ford did on their focus RS vehicle; the intercooler was too efficient, so in true Ford fashion, they reached into their part and they came up with a roughly 3“ x 3“ piece of plastic that had adhesive on the back of it, and they simply placed it on the intercooler.

[Showdown]

Originally Posted by wprater

It will constantly flow through the cooler, but only go back to the tank after temp (around 180F) opening an annulus. Here is a great description and illustration of how the aux thermostat works.

https://forums.pelicanparts.com/porsche-911-technical-forum/927332-how-external-oil-thermostat-works-illustration.html

This operation is inconsistent with the diagram in the post you quoted and the functionality of the thermostat valve.

Oil under 180F from the engine should flow back to the tank, not to the cooler. Only after the oil from the engine is above 180F should it flow from the engine to the cooler and then back to the tank.

It sounds like the thermostat is installed incorrectly if that’s even possible, or that it plumbed incorrectly (more likely)


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[brighton911]

I second what Showdown said. Oil shouldn't be going to the cooler circuit until the temperature exceeds the thermostat set temp. Even then, the thermostat throttles the amount of oil going to the cooler to maintain temperature.

[stownsen914]

What Brighton said. If the thermostat is plumbed correctly and operating at it should, there is no oil actively flowing through the cooler and it's not cooling the oil. So covering the cooler shouldn't do anything.

But do the experiment as a troubleshooting step - cover the cooler and see if it makes any difference.

I saw in an earlier post that you've tested the thermostat, but the symptoms you're seeing seem to point to something wrong in your scavenge circuit.

[Jeff Higgins]

Wil, it's easy to see where there may be some confusion regarding the thermostat/oil flow diagrams that you linked. Yes, the thermostat is always open feeding the inlet side of the cooler. That does not mean that oil is flowing to the cooler, however. It cannot flow when cold because the thermostat blocks the outlet side of the cooler, the side through which oil returns to the tank from the cooler. Two ways to accomplish this - block the inlet or the outlet, both result in zero flow through the cooler. Porsche chose the latter.

So, yeah, you have either a thermostat or a plumbing problem. That cooler should be at ambient temperature at the oil temps you indicate.

[wprater]

Thanks for the clarity; I was misrepresenting that. There is pressure, but no flow.

I will double-check the plumbing to the thermostat.

[stownsen914]

I think you confirmed this previously, but you're sure that the oil temp gauge is correctly measuring 155?

['78 SC]

OP, I have the same setup: 965 type filter instead of the on-engine cooler, nose-mounted Setrab cooler (no fan), and stock thermostat in the RR fender. I went for a drive today and had no issue with oil temp even though ambient temp was 50F. I think you have a problem with the thermostat, the oil line plumbing or you measurements.


10C (50F) ambient temp
22C (72F) initial oil temp (car stored in garage)
85C (185F) oil temp stabilized after 15 minute drive
90C (194F) oil temp after 2 WOT pulls in 3rd (maximum temp observed)
80C (176F) lowest temperature observed during return trip.

These temps are all from my ECU. The instrument panel gauge approached, but never exceeded the 210F mark.

The engine is an EFI 3.2 short stroke with ITB and dual OOP.

[wprater]

Thanks for looking into this and verifying the temps over various operating conditions and being so thorough.

I will do similar tests when I get the car back down from the lift to fix a few other things.

Using an IR heat gun to verify temps at exits from auxiliary thermostat. I won't rely on the VDO gauge.

The plumbing to the thermostat is routed correctly. I'm not sure if the plumbing to the cooler will make a difference.

The sizes/cooler I got from the PO, but I did not verify the receipt. I can try to count the rows in the matrix to get a better assessment.

My engine is a 3.2 SS with very high compression and running PMO 46 carbs.

['78 SC]

One test I did not perform yesterday, but have done many times before, is to let the car idle and watch the oil temp. It will rise steadily, even with full oil flow through the cooler. I have to use a fan or drive the vehicle to force air flow through the cooler or it will overheat just idling. Maybe you can perform a similar test to to baseline what is happening with yours. Note the temperature at which there is flow through the oooler.

I did a similar test on my 1978 a few months ago to check operation of the cooler. That car has a stock an on-engine cooler and a Carrera front fender cooler (no fan). All temps except "Gauge" are measured with an IR gun. "Sensor" refers to the temp sensor screwed into the R chain case. All others measured at the external thermostat.

Time	Gauge	Sensor	Scavenge	To Tank	Cooler	Cooler
1	<120		78	80	78	75
5	<120	117	95	93	73	73
10		119	119	112	75	75
15		148	140	140	75	75
20	175	164	143	140	75	76
27	180	174	179	181	179	181
35	180	182	175	175	187	189
40	181	189	197	182	192	195

comments/observations:

• External thermostat appears to open around 180F (as expected).
• Fender cooler doesn't do much when car not moving.
• Don't take the IR gun too literally - the surface properties can affect the reading.

This test and my general experience idling the car that has no on-engine cooler make me suspect you have an issue with the thermostat.

I mentioned the plumbing before because the on-engine filter interferes with some generations of scavenge lines (there are at least 3) and racers often replace it with flexible lines which could be routed different than stock lines.

Happy hunting,
Steve

[wprater]

Comprehensive test, thanks for sharing.

I just did a 30 min drive and 5 mins of idling.

I confirmed that both the inlet and outlet lines from the thermostat were at ambient temperature (70°F) after startup and a few minutes of idling.

After 15 minutes of driving, the oil line temperature to the thermostat was at 145°F, and the oil was not flowing to the cooler.

After 30 minutes of driving, the oil temperature from the engine to the cooler is about 165°F, and it is flowing to the cooler. It was 93°F coming back to the tank from the cooler.

I'm not sure exactly when the thermostat is opening up, but I just replaced the guts of it, so it should be operating correctly.

The gauge is still sitting at the top of lower box at ~160 F.

[Showdown]

If the thermostat is opening at 165°, that’s not operating correctly.

[stownsen914]

A couple thoughts:
- I assume you are measuring the temp of your oil lines using an IR device on the outside of the lines, yes? It's worth keeping in mind that the outside of the lines probably don't represent the full temp of the oil inside them. 165 deg on the outside of the line could easily be 180 or more inside.
- How sure are you that the gauge is correct? It may be worth bench testing the gauge/sender.

['78 SC]

wprater,

15 minutes of moderate driving is about what it takes mine to get the whole system, tank contents and all, up to temp so yours could still be running a bit cool and not up to steady state conditions at 15 minutes.

Your 30 minute readings appear to have the system warmed up. The temperature difference between the two lines to the front cooler confirm you're getting flow through it. It certainly appears your thermostat is opening around 165F. The gauge confirms that, right.

If you want to see the exact temp at which the thermostat opens, idle the car and record temps at intervals. It should be apparent when the thermostat opens and the lines to the cooler warm up.

Steve

[Duc Hunter]

For the record I am running a very large oil cooler on my 964, and the factory 1975 fender mounted thermostat. See My thread here for the oil cooler pice, etc). My car warms up to 80C on my gauge and sits there. In very cool weather it will sit with the needle just below the 80C white line. With a properly running thermostat yours should too. So covering the oil cooler is not an option, it is a bandaid.

I checked my oil temp gauge when I built the oiling system using an IR gun. I shot the oil temp sensor (on top of the engine), the piece it mounts to, the oil like fitting that feeds the external thermostat at both the thermostat and at it’s connection to the pipe that feed oil out of the engine. Once everything warmed up they were all within a few degrees C. Remember to, if you just let it warm up via idling it can take 20 min or more to warm everything up. The return lines may not get to “temp” sitting there, so I only worried about them feed line from the engine to the thermostat. Also remember the exhaust will radiate heat into the fittings near it.

If you validate that is it not a sensor problem (almost always a sensor, and not the gauge), then it’s a thermostat problem for sure. The external thermostat on my car was stamped for 83C. I believe (not sure) that the engine thermostat should be open first and there for should be a lower temp.

My 964 engine does not have the engine mounted thermostat as it never had an engine mounted oil cooler. The purpose of that engine thermostat is to circulate the oil in the block and not though the engine mounted oil cooler, until it’s up to temp. Once they oil cooler “cannot keep up,” meaning the oil that passes out of it is above its set temp, then the oil starts heating the external thermostat, to them flow oil to the front of the car.