Front Center Oil Cooler is keeping my temps too low

[wprater]

Hi,

I'm concerned that my large Setrab 172 center-mounted cooler is keeping my oil temps too low. This is driving around in 60-70°F ambient temperatures in city or spirited canyon driving.

I studied how the auxiliary t-stat works and replaced my internals of the t-stat as well. I was concerned it was forced open. Now I'm concluding that the cooler is too efficient and I need to block off portions of it.

Another thing to note: I do not have an engine oil cooler; I have replaced it with an oil filter console.

Im getting about 155 F max at the lines to the entrance of the external t-stat now. I'm worried about continuing running the engine hard at these temps and I cannot get them any higher.

What is an elegant and reversible way to to block off the cooler to see if I can get my temps up?

[Bill Verburg]

Originally Posted by wprater

Hi,

I'm concerned that my large Setrab 172 center-mounted cooler is keeping my oil temps too low. This is driving around in 60-70°F ambient temperatures in city or spirited canyon driving.

I studied how the auxiliary t-stat works and replaced my internals of the t-stat as well. I was concerned it was forced open. Now I'm concluding that the cooler is too efficient and I need to block off portions of it.

Another thing to note: I do not have an engine oil cooler; I have replaced it with an oil filter console.

Im getting about 155 F max at the lines to the entrance of the external t-stat now. I'm worried about continuing running the engine hard at these temps and I cannot get them any higher.

What is an elegant and reversible way to to block off the cooler to see if I can get my temps up?

Just partially cover the cooler

[TwoBluPorsches]

Originally Posted by wprater

Hi,

I'm concerned that my large Setrab 172 center-mounted cooler is keeping my oil temps too low. This is driving around in 60-70°F ambient temperatures in city or spirited canyon driving.

I studied how the auxiliary t-stat works and replaced my internals of the t-stat as well. I was concerned it was forced open. Now I'm concluding that the cooler is too efficient and I need to block off portions

Im getting about 155 F max at the lines to the entrance of the external t-stat now. I'm worried about continuing running the engine hard at these temps and I cannot get them any higher.

I’m confused because I would have figured that a working thermostat would only allow oil to flow to the cooler when the oil temperature reached 190°. Are you looking to block off the cooler as part of your troubleshooting?

If the line to the cooler is at a temperature less than 190° I’d blame the thermostat because it’s my understanding that oil should return to the tank without going to the filter unless the oil is >190°

Do the lines after the thermostat going to the filter measure 155°? What is the temperature of the return oil?
Does the engine mounted temperature sender agree that the oil is only getting to 155°?

I’ve got factory coolers including a 3.2 front fender cooler with stock thermostats and I’ve driven on days with below freezing temperatures. The gauge always indicates temperature in the 180 to 190 range

[ard]

(Mostly) unrelated but I remember that on a Citroen 2CV one was instructed to install a "grill muff" (yeah, say that with a straight face at the parts counter ;-) ) over the front grill during cold seasons to prevent the air cooled engine from running too cold and not reaching operating temperature. I suppose you could fashion a simple shunt out of aluminum and fasten it temporarily with zip ties to root cause whether that raises the temperature at the thermostat.

[stownsen914]

Agreed that if your external cooler plumbing is correct with a working t stat, it should run at the t stat opening temp. Worst case if the cooler is too big is that the t stat does some extra work to keep the system at operating temp.

[stownsen914]

A couple things:
I'd agree that 155 is a bit cool to run the engine hard for extended periods.
Sounds like you've measured temps at different places. 155 degrees at the t stat inlet? That's awfully cool.
The t stat should not even open at 155. So your front cooler should be cold at that temp. Is that the case?
If you do need to test covering the cooler, you could cover the cooler opening with strips of duct tape temporarily. Crude yes, but only for testing.

[pmax]

A thinner oil perhaps ?

[brighton911]

It has to be the engine thermostat letting oil flow to your cooler prematurely. I was also having trouble with low oil temps on my stock 3.2 I pulled the engine oil thermostat, did the hot water check and it operated as it should. Re-installed the thermostat and same low temp. Replaced the thermostat with new and problem solved. Doesn't make sense to my practical mind either but I rationalized that it could only be the engine thermostat and it was.

[stownsen914]

He mentions no oil cooler on the engine, filter there instead

[bpu699]

What exactly are we calling low oil temperature on the gauge? I see threads on the 930 forum that running mid gauge is "too hot" and will cause damage. Mine runs at the first tick mark, and I too have a large front cooler... First tick mark is about 194 degrees I believe...

Also, measuring the outside temp is not the same as the actual oil temp...

See pics in this thread...

https://forums.pelicanparts.com/porsche-911-technical-forum/402203-my-oil-temperature-too-hot.html

['78 SC]

You mentioned several temperatures - what is the temperature per the gauge of the oil in the engine? Have you confirmed that temperature with another device?

The oil will lose some heat passing through the line to the front cooler. If the thermostat is mostly closed, the low flow could give the oil a chance to cool significantly on its way to the cooler and give a low temperature at the cooler inlet. The low flow would limit the amount of heat rejected by the front cooler. What's the oil temp at the thermostat exit going to the front cooler?

You are using the stock external cooler thermostat, right? Not the Mocal thermostat. The stock thermostat receives the full flow of oil directly from the scavenge line and can respond to the actual engine oil temperature. I'm not familiar with the way the Mocal thermostat is plumbed in

I have the same set up with an on-engine filter instead of a cooler and the stock external thermostat, so all oil cooling is via the front cooler. It works fine at speed (track car), but cannot idle very long without getting hot, since there is no airflow through the cooler. I use a fan and maybe water spray when testing or doing dyno runs.

[wprater]

I switched to a thinner oil (30 wt) after rebuilding the thermostat. Temps may have risen 5 deg, but nothing substantial.

The low temperatures per the gauge are just barely at the top of the bottom white box. I have tested the gauge grounded to see that it will achieve full range.

From what I understand, the oil will flow from the motor through the inlet of the thermostat, through the cooler and then to the closed gate on the thermostat. This is a lot of surface area for the oil to cool and keep that gate closed.

I now plan to block off 1/3 of the front surface area of the cooler with some radiator zip ties to see if that will raise my temps.

[rwest]

Are you just testing by the gauge reading? Maybe your sensor is not correct for your gauge?

Do you have an IR thermometer you can point at a few spots to verify? If not, they are really cheap to purchase.

[Matt Monson]

Duct tape. Start by blocking 20-25% of the cooler and go from there.

[wprater]

@rwest I have been using an Fluke IR thermometer to test in various places. It should be pretty hot when exiting the engine before flowing through the thermostat. But the cooled (90F) oil coming through the other side of the loop is likely equalizing the temp at aux. thermostat and never allowing it to open.

[wprater]

Lots of air flow. I’ll try blocking it off and report back.

[brighton911]

wprater, you stated there is no engine cooler but is there a stock engine thermostat in your setup ?

[wprater]

There is no engine thermostat installed as the oil flow is forced through the filter console with 930.107.767.02. Used on the 964 Turbo which also had a secondary oil filter console.

[rwest]

I don’t have an external cooler, so just throwing out ideas that may or not be useful!

Any chance that the thermostat is plumbed backwards? It seems to me that the oil shouldn’t go to the cooler until it is hot enough. From reading here, but maybe I read it wrong, it sounds like the oil flows out to the cooler all the time, but doesn’t return until the thermo opens?

[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