Moonraker

I did order a whole thermostat from Pelican based on the table of part numbers in Adrian's book that identifies the insert being only for MY 92-94 thermostats. Mine is a 90. Is an insert available for the 89-90 thermostat PN 964-207-047-03.

JasonAndreas

PET shows 964-207-349-02 as the correct insert but superceded part numbers aren't always 100% backwards compatible and I trust Adrian's book more than I trust PET. I would drain the oil (recycle if its not too old), pull the locking ring on the thermostat and look at what you already have before ordering a whole new assembly. You might get away with just cleaning out the sludge that has built up on the insert and not have to replace the whole unit. I would do whatever I could to not have to replace the whole assembly, the connected oil lines are not fun to play with. btdt

Moonraker

Jason, thanks for the part #'s. I like the remove, inspect , and clean approach for the insert. This will be the project for tomorrow.

Bill Wagner

Bob:

It's normal for the oil pressure to drop as the engine warms up (like you described a few posts ago).

As I think about this problem, a few things occurred to me:

1. If there is a clog, then the oil pressure, with respect to the direction of oil flow BEFORE the clog will be extremely high, and the pressure after the clog will be low. It occurred to me that if this is the case, then it might actually cause your oil pressure release valve to pop open (depending on where a clog is), which will certainly cause your pressure to drop. I would think you'ld be able to detect this on your engine since it will be dumping at least a little oil....how much I don't know.

2. I seem to remember reading somewhere (probably on this site) that some after market oil filters (Fram seems to ring a bell in my mind) can be problematic. If I recall correctly, I think someone actually had a non-Porsche filter disintigrate, causing all types of problems. You might want to check the filter and make sure it's OEM. Even if is is OEM, things can still fail, probably just not as likely though (I hope!!).

3. A STRONG smell of gas in the oil could indicate dillution from a bad injector...meaning your oil is just being thinned out by gas being dumped in the oil. Your car is old enough and has enough miles on it for this to be possible (usually a fuel injector stuck wide open).

Hope this helps,

Adrian

Dear Jason,
This is 100% correct and it is getting worse. The new PET (PDF version) has had a huge amount of data removed from it compared to the old one. Clearly meaning that many parts have been discontinued.
Many of the 996 replacements now being sent out as "compatible" do not fit and require modification to the car.

Changing the thermostat is a very messy job which requires draining off all the oil anyway.

There are companies around that will just replace the bi-metallic switching device.

I reckon you will be really lucky to find an original p/no thermostat for a 1990 model year.

Ciao,
Adrian.

PS: The 993 owners will also face similar problems with many 996 parts now being offered as replacements as well.

Moonraker

Ok, made a little progress at lunchtime. Oil is drained and thermostat insert retaining circlip removed. How on earth do you remove the insert in a non destructive fashion?? The end plate is resesed in the bore and is made of non magnetic aloy so the giant magnet aproach won't work. For now I heve removed all the surface corrosion behing the circlip retaining grove and dosed the whole area with PB Blaster. Also removed the pressure relief valve that is integral to the assembly and all looks clean in that area.

Rgds:

Adrian

Dear Bob,
The only way I know to get it out is to drill it out. However I do not recommend you do this unless you have all the right parts to re-install so you can see what you have to do.
I have not seen this done with the thermostat insitu either.
Ciao,
Adrian.

Moonraker

My new cunning plan is to epoxy a fitting to the end plate and see whether I can remove it with a slide hammer.

Probability of sucess is not high but I figure it's worth a shot.

Moonraker

Removed the thermostat from the car and used Jason's "drywall screw in the end cap" removal process. Thanks to Jason for the tip, my end cap was pretty well coroded in place.

The findings: The very sharp edge of the thermostat "shuttle oil orifice" (my term) had worn a ridge on the machined alluminium bore that it moves in which caused the moving part of the thermostat "shuttle" to hang up between its open and closed position. The effect of this is to significantly reduce the return line flow capability to the tank causing the pump essentially to cavitate.
I'm pretty sure that is what was happening as when I drained the oil there were about 8 quarts in the crank and only two that came from the tank.

The proof of the pudding of course will be when the new thermostat is fitted, part is on back order at the moment.

As a side note my thermostat came off pretty easily but this would be a very challenging removal without a set of low profile 36mm wrenches.

Thanks to all for the tips along the way.

Rgds: