944 oil pump losing prime

OPRN · 04-24-2016, 05:05 AM

Hi all,
I'm new to this site and have a question that perhaps someone can shed some light on. I have an '83 944 that seems to take far too long to get oil pressure when it is started after not being used for a while. If the car is used daily there is no issue but after sitting for a few weeks the oil pump seems to lose it's prime and takes far too long in my opinion to deliver pressure.
Any ideas?
Thanks for considering this concern.
Merv

dgcantrell · dgcantrell's Garage

What weight of oil are you using? How much time is it taking to pick up oil PSI?

v2rocket_aka944 · 04-24-2016, 08:23 AM

If the car has been sitting, simple trick is to unplug the ignition coil wire from the distributor cap, crank the engine over a few times until you see oil pressure, and then plug it in and start the car.

dgcantrell · dgcantrell's Garage

Excellent suggestion.

John_AZ · 04-24-2016, 09:20 AM

You are now using the correct oil filter?---with the correct anti-drain back valve?

OEM Porsche or Mahle OC142.

J_AZ

OPRN · 04-24-2016, 07:08 PM

5/40W synthetic oil, Not sure about the filter - good suggestion - I will check.
Pulling the coil wire I don't think is an option as two things are likely to happen. 1) run out of battery before oil pressure came up, 2) probably flood the cylinders with fuel.
It takes about 15 seconds running at idle to get pressure. When previously run that day it's only one or two seconds.
Once the pressure is up it pins the gauge at idle and stays there until fully warm. I have never seen it less than 2/3 up the gauge even coming off the highway at idle.
Thanks all for your prompt replies!

devin3200 · devin3200's Garage

Just chiming in. But I've had this same problem but this was after I changed my oil and yes I used the Mahle OC142. So I'm sort of puzzled as well.

John_AZ · 04-26-2016, 09:44 AM

A good post to review:
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/883635-no-oil-pressure-cold-start.html

J_AZ

OPRN · 04-27-2016, 01:20 PM

Thanks for the link John, looks like there could be more to it than I had hoped. First step is a new filter and oil.
I just picked up an 85 944 and it definitely does not have this issue!

v2rocket_aka944 · 04-27-2016, 02:55 PM

Quote:

Originally Posted by OPRN

5/40W synthetic oil, Not sure about the filter - good suggestion - I will check.
Pulling the coil wire I don't think is an option as two things are likely to happen. 1) run out of battery before oil pressure came up, 2) probably flood the cylinders with fuel.
It takes about 15 seconds running at idle to get pressure. When previously run that day it's only one or two seconds.
Once the pressure is up it pins the gauge at idle and stays there until fully warm. I have never seen it less than 2/3 up the gauge even coming off the highway at idle.
Thanks all for your prompt replies!

2 things...
1) if it isn't currently snowing and/or below freezing temperatures where you live, you should be running a 20W50 oil (or similar). that is part of the cold oil pressure problem.
2) with the coil wire unplugged, even if the car has been sitting for weeks, it should take maybe 5-10 seconds, tops, for the starter to turn the oil pump enough to get pressure on the gauge.

something is up...if the car was running for 15 seconds without any oil pressure, it'd be making one big ****ing awful noise. perhaps the gauge or sender is screwy??

OPRN · 04-28-2016, 02:36 PM

Yes we are still getting overnight temperatures around or slightly below freezing. I was running that oil because that is factory spec for our VW turbo diesels year around. I thought if it was good enough for that severe service it should work in a naturally aspired gas engine. Simple matter to change though.
The gauge and sender are fine because as you said the lifters tell me when the engine gets pressure and the engine RPMs also drop when the pump starts to move oil. It all corresponds nicely to what the gauge tells me.
Now that I think of it the same thing happens on start up on any vehicle I have ever changed oil in until the filter fills. So perhaps it in the back flow valve in the filter.
I don't see the suggested filter number on this site do you guys get yours elsewhere?

emoore924 · 04-28-2016, 05:27 PM

So, when you start the car, does it make a LOT of valve noise when you start it for all 15 seconds? Does it clatter until the oil pressure gauge comes up or does it sound normal when you start it, no funny noises, then suddenly the gauge moves?

I used to have a Ford 5.0 that would do this. It would start, sound normal, and the gauge would read zero for anywhere from 15 seconds to like 2 min. It was the oil pressure sensor. Nothing wrong with the oil pressure.

If it sounds normal, no clatter, I'd say sensor or gauge or wiring or ground...

OPRN · 04-28-2016, 08:00 PM

Quote:

Originally Posted by OPRN

The gauge and sender are fine because as you said the lifters tell me when the engine gets pressure and the engine RPMs also drop when the pump starts to move oil. It all corresponds nicely to what the gauge tells me.

There you go.

v2rocket_aka944 · 04-28-2016, 08:48 PM

How much oil do you put in with an oil change?
The most common cause of low oil pressure I've seen in 944s, after bad sender/gauge, is simply under-filled.

A 1983 should take 5.5-6 qts IIRC.

OPRN · 04-29-2016, 08:49 AM

I go by the marks on the dipstick, should be ok? Even if it was 1/2 full it should not effect the pump getting prime on start up.

OPRN · 04-29-2016, 08:55 AM

Devin 3200 did your problem persist after the initial start up when you did the oil change?

devin3200 · devin3200's Garage

OPRN: Yes the problem is still there. It takes if don't touch the pedal about 15 to 20 seconds til the light shuts off and the pressure comes up. This is only on cold starts. Now I didn't have this problem before I changed my oil. I used synthetic I believe 30 weight the first time with a fram filter. Than I read about the Mahle filter. I went back in and replaced the filter and oil again. Plus primed at the filter outlet like I read up on, but still the same.

sausagehacker · sausagehacker's Garage

Quote:

Originally Posted by OPRN

The gauge and sender are fine because as you said the lifters tell me when the engine gets pressure and the engine RPMs also drop when the pump starts to move oil.

Possible that the oil pump is not being driven until some friction/heat build up? It's friction driven by the belt drive cog piece. Make sure that your crank bolt is torqued to spec (155 ft lbs?)

OPRN · 04:10 AM

Ok! I didn't realize that the oil pump is belt driven. I could check that out. Thanks!

Just thinking now - as I haven't been into the timing belt end of things yet - does the crank pulley not drive the timing belt? Is it not keyed to the crankshaft? Or is the oil pump driven off an accessory belt?

I'm thinking it's time to get a repair manual!

jeffrsmith · jeffrsmith's Garage

Michael is not saying that the oil pump is belt driven, it is driven by the pressure fit afforded by the crank bolt, this is the reason that the first thing you should check is the torque of the crank bolt - especially if you have done any work on seals.

Clark's Garage has a lot of good shop manual info and troubleshooting tips - http://www.clarks-garage.com/