I have a '75 1.8 with stock FI. Engine is completely stock. I've had the same problem for quite sometime.

Basically after driving it on the freeway or just for a long enough time the oil light starts flashing at idle. If I rev the engine up it disappears. If I put it in gear and revs go up it also disappears. Seems like an idle only problem. This disappears after engine cool down if I turn it off.

Oil level seems normal (I'll recheck) and engine sounds exactly the same with or without it so I'm guessing it's some sort of a sensor somewhere going a little crazy after heating up on the freeway. Any more specific thoughts? Anybody had a similar problem?

Oil pressure switch? Oil too thin? (Do you use a different brand of oil nowadays?). Or indeed a sensor with a mind of its own.

What happens when you start the engine first thing in the morning?

An easy way to check the health on a Saab 96 engine, so perhaps good for the boxer as well: How long stays the light 'on' when starting the engine? The shortest possible period is good: enough pressure from the start.
Second test: start the engine (cold) and turn it off the moment the engine runs and the o/p light goes 'out'. Turn the key back to 'contact' and wait for the o/p light to come 'on' again. The longer that period, the better it is.

Easy test: change the oil for oil with a different viscosity - still within Porsche's specs off course. Older engines tend to do well on 20w50 - make sure it contains the correct level of ZDDP.

M.

Some good points here, thanks. I'll check this out. The car might be due for an oil change anyway. I bought the car in November and only drove it maybe 1000 miles or so (odo is broken), therefore oil hasn't been changed yet. Oil light seems to behave relatively well, this condition only occurs after a prolonged run as stated.

It sounds like the pressure is too low when hot. This can be too thin oil in the engine, or signs that the engine is deteriorating. I would get an oil pressure gauge and check the pressure cold all the way up to operating temp. You could do this with old and new oil to see what difference it makes.

Skoot

Not uncommon when hot from what I've heard over the years. Agree about potentially switching to a thicker oil. I run 20-50 in the warm weather out here which helped prevent this when I had a stock 2.0.

I assume if you bring the idle up 100-300 RPM the light goes off. Speaking of which, what is your idle speed?

You might want to consider adding a gage in order to know for sure what is going on.

I once had the same problem. Changed the oil pump, oil pressure relief valve, oil pressure switch nothing fixed the problem. I got rid of the Fram oil filter it has been fine since.

Switch to 20w-50 oil. Joe Gibbs or Brad Penn Race Oil, or one of the other ZDDP formulated oils that you usually cant find at your FLAPS.

I tend to order Brad Penn by the case every other year (when my car is running).

Zach

My oil light does the same thing with both Brad Penn 20w-50 and Joe Gibbs Driven 15w-50 synthetic. Fortunately, I also have a double sender and an oil pressure gauge. When my oil heats up and the light comes on, idle is normally at about 700 RPM and the gauge shows about .8 kiloponds per square centimeter, which converts to about 11.4 psi. This condition usually occurs when the oil temp is 215-220 and the cylinder head temp is 280-290 on #3... basically after long stretches of 75-80 mph driving on 80+ degree days.
11.4 psi at 700 rpm is fine. The dash light is just not precise enough. Worry about it if the light doesn't go out when you give it some gas.

also Valvoline VR1 racing oil, 20w50 has the correct ZPPD #'s and can be bought at your local FLAPS store, got mine at autozone.
in some studies it has tested better than the brad penn oil for wear protection etc in racing conditions.-

Phil

one of the factors to look at when comparing oils for our cars is the PSI numbers.
The higher the number, the better the "load carrying capacity/film strength"

VR1 is higher in this category than either Brad Penn or Joe Gibb's, and that is why i decided to use it.

The owner's manual says that the light flickering on at hot idle is normal. I'm not convinced it's normal, but I think it is acceptable. It can happen if your oil is too hot (oil thins out as it gets hotter) or if it is too thin in the first place. It can also show that the pump is a little weak, or the main bearing clearances have grown slightly. Those are normal wear for an engine with some miles on it--but they are wear and would show that there are some miles on the engine.

If the light comes on clearly and stays on, that is a real super urgent problem which means you need to turn the engine off NOW!

If the light comes on somewhat during braking, it probably means the oil level is a quart low because somebody forgot how to count to 4. (Don't ask how I know this.) If it comes on in cornering, it means your tires have enough grip, but that you might want to consider a "tuna can" or a deep sump or an Accusump.

--DD

I think these types of problems may indicate wear/failure in the oil pressure relief valve.

Thanks everybody. Some good stuff here. Will do an oil change sometime.