oil pressure light

[johnpaulny]

My oil light started flickering at stops today. This happened on first test drive after installing new 195 degree thermostat (old one was lower). The water temp was fine - the needle finally made it into the lower third of normal range. What is very concerning is that I heard a new tap after the flickering oil light started. The oil level is fine and it doesn't burn any oil. Anyone have ideas about this?

Also, I'd like to test the pressure with an oil pressure gauge. I know the basics about how to connect it but not sure of what gauge fits the car.

[HeadacheGuy]

You have 2 choices here. Either the sending unit is bad and is tripping at a higher pressure at hot idle or your pressure really is bad. Get an oil pressure gauge (any fluid gauge works but get one with readable graduations on the low end - 0 to 100 psi gauge). HOT idle oil pressure is what you want to read. Your sending unit is set to trip around 5 psi. Ideally you want to see 20 to 30 psi. This would be a healthy engine. At 3000 rpm's it should be around 45 depending on the pressure relif evalve but bear in mind even a worn engine will produce this. If the hot idle pressure is way low don't assume it is the oil pump (common mistake). They are a positive displacement gear pump and other than a stuck relief valve would REALLY have to be worn to kill the pressure. Most likely cause is worn main or rod bearings. If it doesn't have a rapping knock on fast acceleration you can probably keep driving without issue but I do recommend avoiding a lot of hard acceleration. The cure? Depends on your pocket book. Best solution is to rebuild it. Bar none. This also covers the possibility that you have worn cam bearings. Second solution is to have bearings put in it in frame. This will work ok but make damn sure your mechanic is damn sure the crank is smooth , if not - back to the rebuild. 3rd solution which keeps the light out and buys you time is run heavier oil with some LUCAS oil treatment. Use a 20W-50 but only during warmer months. Back to the happier possibility - if the pressure is acceptable (even 15 psi hot idle is fine as long as it immediately comes up on acceleration) just replace the sending unit. Hope this helps

[johnpaulny]

Thanks for the detailed response. I'm very confident that the engine is tight. This was a very babied car and my mechanic believes it to be a true 60000 miles. Also, it runs perfectly, and no smoke whatsoever. What I find baffling, and I don't think coincidental, is that it happened just after I replaced the thermostat with a 195 degree unit. I don't know what the other one was but the temp gauge was never in the normal range - always pretty cool. With the new one it is about 1/3 way into the normal range. I did that today and drove it once, on the highway, had it up to 65 (which I haven't done since I got the car). It was after this that I noticed it. Is it perhaps the viscosity of the oil - maybe too thin for the higher temp and that's reducing the pressure? Regarding that, what oil/oil filter do you use, brand and weight? Thanks for you help, John

[HeadacheGuy]

Yes on the viscosity theory. This is wear the Lucas comes in as it is a viscosity stabilizer. I actually run a my bird which has a little wear (cold bearing knock for a second on a really dry start) in the lower end so I run 10w-30 with a qt of LUCAS stabilizer. I bought it this way and actually have plenty of trust in it as it has been on many highway trips. My pressure will get a noticeable drop at about 600 RPM on a real hot day but only if I don't uses the Lucas. As far as filters go, I own a repair shop which is also a NAPA autocare center so I run a NAPA silver oil filter. Note I run the cheaper filter. Method behind madness (we actually proved it) is that higher $$ filters have a finer media for better filtration. Sounds like a good thing right? The down side is it takes longer for the finer filter to flow on cold fire up. On a really cold day we are talking about an extra 2 to 3 seconds before a manual gauge will show pressure. Cold starts ( oh hell.. ALL starts) are where most of engine wear occurs. The coarser (and cheaper) filters still filter down to a fine enough micron to prevent damage. This is to my knowledge to only time I will ever admit to saying cheaper is better. Sorry...standing on the soap box too long.....

[johnpaulny]

I saw info online (not tbird forum, I think maybe chevy) that corroborates what you say about filters. Their thoughts are that more restrictive filters will keep pressure down even after warm up. Good to know. Thanks!