Since I got the GTS the temp gauge was rock solid at about 1/8" to the right of the first white mark.

This spring it started climbing up to about 1/8" to the left of the white mark on the right side of the gauge after hard acceleration, and would stay there until driven tamely for a few miles. Just sitting at idle would not cool it back down. This gradually increased to climbing to just above the right side white mark. I also noticed that the idle oil pressure also dropped from a normal of just below 3 bar to just above 2 bar.

Put in a new thermostat and a new thermostat and back flushed the radiator. The only thing that changed is that it would easily cool back down to just below the white mark on the right side when it started climbing above it.

When auto crossing the idle oil pressure would drop a little after each lap. It would go from the normal 3 bar to 2 bar after 4 laps. Setting between laps with the engine running would not increase the idle oil pressure, i.e.. cool the oil. However, turning the motor off the idle oil would increase eventually back to the normal 3 bar with engine warm. I assume the oil was getting hot and would not cool with the engine running.

This spring when the water temp gauge started climbing above the right side white mark the idle oil pressure started dropping lower. Autocrossing it would get as low as 1 bar, but not low enough that the low oil pressure warning would come on. In all cases revving the engine even 200 rpm off idle and the oil pressure would climb to 3bar and higher. And when driving around town the idle oil pressure started dropping to 2 bar instead of the normal 3 bar.

With the car well warmed up and hot while checking the in car thermostat and cooling fan operation my mechanic noticed the oil cooler line feeding the oil cooler was not very warm. He replaced the oil cooler thermostat and because they were looking their age the oil cooler lines.

Now I have yet to see the temp gauge go above 1/8 inch past the first white mark or the idle oil pressure go below 3 bar.

 

Nice

 

 

Interesting!

 

Do you have the part numbers for the ''oil thermostat'' change?

cheers

 

Interesting- I typically see the water temp to the left of the last white line increasing to the right of it when pushing hard in our really hot weather. Tickover has always settled at 2 bar and less when running Mobil 1 thin stuff.

For the water temp to settle on the rhs of the first line makes me think you are running with a 75C thermostat?

I have never heard of problems with the oil thermostat mechanism and assumed it was more or less bullet proof- maybe not. Same for the oil cooler lines- they are very chunky.

Was it much of a job to change out the the oil thermostat?

Regards

Fred

 

Where is the oil thermostat located?

 

Ive never heard of problems with the oil thermostat, so Im very interested in getting to the bottom of this.

However, for the oil lines, Ive seen and heard of lots of failures.

 

+1. Never knew it had one

 

The Thermastat is under the big round adapter where the line goes into the block.

 

Do the oil temp thermostats go bad very often? heck, if I had known there was such a thing I would have changed it out when I had the engine out (twice in two weeks). Maybe a winter project?

 

The part #s:

928-107-171-01 Spring (above)
928-107-172-02 Regulator insert
928-107-173-00 Spring (below)
900-123-143-70 Sealing ring


It's in the loop before the filter and over time my get some gunk on it

 

Very interesting. At 130K plus miles, it makes sense to change out the lines and T-stat. Thanks for that one Richard, I'll add that to the list.

 

What a great cause/effect report!
Thanks.

Do earlier cars also have this thermostat?

 

All 928s with and engine oil cooler have the thermostat.
You can likely get away with simply opening up the thermostat and cleaning the area and parts.