What is the best oil for my car?

Probably Nox too high. Can also be engine too hot. Last time cooling system serviced? Also can be carbon in the combustion chamber ignites fuel too soon. Fuel delivery system and all sensors may be a problem. Bad or corroded connections can contribute to bad behavior of the ECU.

Fix your car right away, by clicking the link
https://www.reliable-store.com/products/1982-1991-porsche-944-944s2-944-turbos-951-service-repair-manual

PROBLEM IN THE DASH CLUSTER.REMOVE CLUSTER LOOK FOR LOOSE GROUND WIRE SHAKE WIRES SEE IF DASH LIGHT COMES ON.IF WIRES LOOK OKAY.PROBLEM IS DASH CLUSTER CIRCUIT BOARD ITS SHORT OUT.CLUSTER HAS TO BE REPLACED.

hello there
does the noise come from botton of your Porsche?
If yes it could be some loose transmisssion mounts?Or it could be you drive shaft is getting bad.

proporsche

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We had a problem something like this it was because of the oil we were useing try a 20-50 weight or a 10-40 wgt synthetic oil try not to use anything lower than a 10-40wgt

sounds like it could be "knocking from the cam". i would throw a thing of SeaFoam or Marvel Mystery Oil in the oil slot. my knocking went away in 100 miles. the stuff works wonders. Good luck. My knocking used to be very loud the higher the rpms.

Sounds like a possible fuse problem. Have you checked your fuses yet. If not look in your owners manual to see which fuse(s) control your instrument panel, or anything else you are having trouble with. Keep in mind, if a short did occur for some reason, more than one fuse may be blown. When i accidental crossed two door lock wires, i blew 6 fuses, some of which were not even related to the wires i crossed. Hope this helps

sounds like a bad tranny. Gear shifter may be locked, have you checked the tranny fluid?

Valvoline Racing 30 wt. no it should not burn oil ; do a compression test

I'm assuming that this is a 5 speed stick car because you mentioned 80-90 oil. This car has a transaxle, not a a separate transmission and differential. The transaxle houses the transmission gears and the differential all in one housing. There is a drain plug on the bottom a fill plug on the side. Here's a link to one of the best do-it-yourself 944 sites on the web. Click on the "garage shop manual" link in the sidebar and scroll down to "transaxle fluid change".

http://www.clarks-garage.com/