I have a 94 with a 4.9L with 194K miles. It doesn't use any oil between changes and it has no leaks anywhere. At every oil change(4000miles) the oil is still very clean. Recently the oil pressure gauge started dropping all the way down when I would come to a stop. It would start doing this after the engine was warm. I put on a mechanical gauge and the truck shows between 30 and 50 lbs of pressure when driving. At a complete idle (no a/c, etc.) the pressure drops down to about 5 lbs. At idle with the AC on it jumps up to normal for an engine at idle. When the pressure is low, there is no engine noise such as knocking or clattering, etc. The engine does not have ANY smoke coming out of the tailpipe and the end of the pipe stays dry with a white/gray chalky appearance. What could be causing this? I was hoping to hit 200K miles before a rebuild. Thanks for any help.

 

Sounds like some worn crank and cam shaft shaft bearings. You could pull the pan and have the journals miked. With this many miles it is probably due a rebuild. I had the same oil pressure readings on a truck a few years ago and it was worn crank bearings. Good luck.

 

Sounds like you need a rebuild. But in the meantime I would use 20W-50 oil, if you are not already. Did this happen quickly or just gradually change?

Winford

 

how will the 20 w 50 help?

 

It happened quickly,It just started doing it one day and has kept doing it. But I really don't know how quickly because I first caught it based on the "idiot" light.

 

Pancake, the higher viscosity oil will keep the pressure higher at idle. If the pressure fails totally, there will be fatal damage to the bearings and crankshaft, among other components.

I once (1984) had a new Nissan Maxima that ran about 7-10 psi at hot idle. First oil change I switched to Castrol 20W-50. I drove it 155000 trouble-free miles after that.

With one exception, I have used the same oil in everything I have that needs oil, including my lawn mower, and have never had an engine failure. The exception is the new short-block in my 92 Mustang (bought with bad engine) in which I am trying Mobil 1 synthetic.

My present vehicles include 54 F100 with Mustang 5.0 HO EFI,
88 F150 5.0, 91 Explorer 4.0, 98 Explorer 5.0, 92 Mustang 5.0.


Winford

 

[updated:LAST EDITED ON 03-May-02 AT 07:35 PM (EST)] winfordr hi ya,


alright i have this problem too i have an 86 f-150with efi 302 2wd auto overdrive tranny and 33,000 miles and i have this problem too. when you start it it has great oil pressure for 10 -15 minutes and then from there if i let it idle at a stop ligyht or in a parking spot it will slowly drop to nothing ,if i rev it up the pressure slowly builds again(i run 10 w 40 now )


this is the recent repair history :i bought it 2 yrs ago drove it for a while and had a problem with losing oil pressure after 2 minutes of idling . did not want to drive it like this so i parked it . i could not find anyone to tackle the prob for a decent price so it sat parked .i am taking auto tech course at local vo-tech school so i brought it there and i replaced oil pump ,cleaned the pan out (there was valve seal particles inthe pan),cleaned and reused screen assembled everything and changed oil press switch


now i have the above problem will the 20 w 50 help keep oil pressuer at idle for me?