Thanks everyone for your responses and specific psi numbers. Everything seems to check with in specs. That is a load off my mind.
This is why I am a contributing member for life!

Helga (1985 245 with 130K) shows at hot idle: 2.5 Bar. After 700 mile Interstate Highway run: 4.25 Bar at 2500 RPM.

Tico,


Hot idle after interstate run:
http://www.unm.edu/~goatman/oil.jpg

Hot interstate at ~2000 RPM
http://www.unm.edu/~goatman/oil2.jpg

As you can see, the numbers approach your values at speed. If your engine is not overheating, then you should be seeing values a little higher at idle.

Just something to keep an eye on.


Goatman

Those pressures are close to what I see on my son's car (300,000+mi), using 5W30 Mobil-1 synthetic. It shows ~52psi at 2000-2500RPM and between 25-30psi at a 700RPM idle, with oil at full operating temp on a warm day. Bringing RPM's up even the slightest over idle speed gives a quick jump in pressure.

I removed the oil pressure gauge (VDO "Cockpit") from the 83's dash a few years ago at about 150k miles, as the nylon tubing to it sprang a leak and it wasn't really telling me anything new...consistent readings over 10+ years and about 100k mi. At the time it showed pressures very similar to my son's 81 with the same oil and similar conditions, maybe 2-3psi higher.

Differences of 2-3 psi are starting to get into issues of gauge accuracy and one's ability to judge exactly where the needle is!

Given your hot idling pressure of more than 20psi, I think there is a malfunction in your warning light sender. They are designed to turn the light on at something like 7 or 8psi. If the only time your light comes on is at slow, hot idle, it's not likely there is anything wrong with the light wiring.

Switching to a higher viscosity oil is unlikely to accomplish anything except increasing engine wear at cold starts.
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Bob: son's 81-GL, dtr's '94-940, my 83-DL, 89-745(V8) and 98-S90. Also 77-MGB and some old motorcycles.

Those oil pressure #s are ok. A higher viscosity oil would increase them a bit, but not a big deal. The oil pressure light should not be on more than half a second or so after startup. The light is sapposed to indicate NO oil pressure. 21 psi should be way plenty pressure to keep the light off. The sensor may be bad, you might try a new sensor or testing your old sensor using compressed air and a multimeter. Next guess would be an intermittent wiring problem, bad wire insulation common. You might try a test wire to the sensor and monitor this with a multimeter with eng running and then driving.
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85 240

Rico,


At very hot idle, as after a highway run, my engine oil pressure gets little below 40psi. With fresh oil, this value is unseen. 20 psi is not a bad value per say, the engine is certainly not being harmed by it, and certainly so with good quality synthetic oil, because the oil film is intact across the babbit. The oil film is either present or tearing, and i expect with great oil, the engine would suffer no damage at even 5 psi idling.

The problem here is that the defect causing the low pressure could worsen suddenly. It's likely cause is the oil pump supply tube o-ring. If this were to pop out completely, your engine would suffer severe damage very quickly.

I would keep a close eye on the oil pressure from now on, until you have the option to remove the engine and make an inspection.


Goatman