Delayed Oil Pressure on Start
 

In the last few weeks when starting my car (1990 300TE 4MATIC) first thing in the morning (cold from -20 to 35 F) or after sitting for a while the oil pressure gauge takes about 5 - 15 sec to come up to pressure. This morning I had the door open and I heard the valves knocking until the pressure came up (yikes!). Otherwise, gauge & pressure appear fine. Car runs fine, starts fine, regular oil changes etc. 10w30 oil and Mann filter. Have done some research here, wondering if this could be my oil pressure sending unit or possibly oil pump. Also, I'm planning to install a block heater soon. Any ideas greatly appreciated. Thanks!

First I was going to suggest checking your oil pressure sending unit, but then you said you heard the valves knocking that makes it a more serious issue. I'd look into it soon before driving it too much and possibly cause more serious problems. Have the oil pressure checked mechanically at the sending unit (install a mechanical oil pressure gauge and see how much pressure you get when you first run engine after being cold). This should give you an idea. Sorry I can't help you more on this. I am sure some qualified tech out there can give you additional help. For now, just keep your eyes on the oil pressure gauge while driving. don't want to drive on no oil pressure or your engine will seize and you'll be looking at new engine!

Good Luck.

Thanks, pretty much what I'm going to do. It only does this on cold start for 5-15 sec. which is making me think not enough pressure in pump or something on start? Otherwise, oil pressure has always been in acceptable range (1.0 -3.0). Turns over on first or second crank always. also 107,000 miles on car.

This is based on a vague, primitive memory so I could be wrong. Hope it's this simple, though. Sounds like your oil filter is draining out to the sump when parked for a period of time. I believe there is an "anti-drain rubber" in the spin-on supposed to prevent this. Change the spin-on oil filter and see if this doesn't do the trick

Thanks! I hope this is it. My car is going in to the shop tomorrow to have the oil pressure problem checked. I'm having the oil & filter done too as it's almost due, so we'll see. I'll post when I find out.

Oil pressure should be up in a couple of seconds. I don't think it is the filter (unless it is damaged) causing such a problem. It could be the sender but by hearing the valvetrain noises, it sounds like a serious problem. It could be one of the oil tubes or tired oil pump. Once you start the engine, does it just stay at 0 or does it move and then fall. For sure, take it for a checkup and don't drive it too much.

My 260E (290,000 miles) does this every morning for a few seconds. I asked numerous mechanics who simply told me that it is cold and for the few seconds until the oil is pupmed upwards the knocking is caused (not hard knocks but rather light) and not to worry about it at all. Actually my car does not use any oil and I just drove it to Los Angeles and back over a 2 week period and we did it without any problems (4000 miles).

Igor Zeljic, Minneapolis.

Yes! this is exactly what I was experiencing. So, I had the oil & filter changed, my mechanic said he thought the filter might have been defective, it is now running fine. Thanks for all the info on this!