Matt O.

Hey fellas,

I just changed the oil in the ol' 944 (89 NA). I had lifted the front end up to get to the oil pan but forgot to lower it all the way...

So when I added the appropriate amount of oil, the dipstick showed alot because I think some didn't drain due to the fact the front was lifted up, and the pressure ran high even after a min or two...

After I realized what I did, I immediately drained some oil, making the dipstick right in the middle...

Yet my pressure still, at idle, is at 2.5.

Last week I had to get a new oil pressure sending unit, put it myself. Before that failed idle was about 1 bar. After the new one idle is at 1.5 bar...

Now idle is at 2.5 and sometimes 3. Yet the dipstick shows dead center.

HELP??

Thanks in advance!!

Dennis Wilson

Did you change oil viscosity? Had the old oil broken down from heat or frequent short trips?

Tabor

From everything I have read, your oil pressure at idle when warm should be between 2-3 bar. With Castrol GTX 20w50, I get about 2.5 bar most of the time (at idle). Unless it is hot out, then I get ~2 (at idle).

944 Faq, section 8. Take a look at 8.1 "Where should my oil pressure be at when cold? warm? idling?"

[ 06-24-2001: Message edited by: Tabor Kelly ]

Matt O.

I'm still using 10w40, like last time.

I drove to Florida and that was about 2000 miles total. Could that have anything to do with it?

Thanks Tabor, I'll look at those FAQs.

Greg Hammond

My engine has a new oil pump, new bearings, new bushings, etc - and reads 2.5-3 bar when HOT, and 5 bar when COLD at idle. I think your pressure now is normal, and was "low" for some reason before.

FWIW: If an air bubble gets inside your oil pressure sending unit, it will read lower pressure than actual. It's possible your tilting of the car allowed the air in the sending unit to evacuate, and consequently you might be reading higher pressure now.

Another less likely cause is the viscosity of your new oil is wrong - maybe it came from a bad lot, and was really 20W-50 instead of the 10W-40 you usually run.

BTW: I run 15W-40 and will be switching to 20W-50 after I get about 20K miles on this engine. You may want to consider going to a higher viscosity for better protection in the future!

Greg

Matt O.

Can you quick explain why it would be better for 20w50 then 10w40?

Thanks alot,
Matt

Greg Hammond

The higher base viscosity of the 20W-50 is going to provide a "tougher" hydrodynamic wedge between the rod bearings and crank, and little-end bushings and piston pins.

Motor oil lubricates by providing a "gap" between two flat metal faces, just like the fine layer of water underneath an ice skater's blades. If this later gets "smooshed out" by the downward pressure of the piston (translated through the rod) under force, what you end up with is metal-to-metal contact, and dramatically increased wear rates.

The benefits of 10W-40 over 20W-50 are slightly better fuel economy, due to the oil being "thinner" and providing less surface tension resistance between moving parts and the oil film that separates them. 20W-50 benefits you by providing a "stronger" film that better resists the "smooshing out" effect of high force.

20W-50 doesn't flow real well in cold climates. The only reason I wouldn't run 20W-50 is if you're going to be starting your car in < 35 degree F weather. If you live in an area that gets cold in winter and hot in summer - change your oil at least in the fall and spring, whether mileage dictates it or NOT. 10W40/15W40 in the winter, 20W50 in the summer.

Greg

Matt O.

Wow thanks Greg, that was kind of you to explain it for me.

I live in NC where it can get 95 in summer but 5 in winter so I'll do just that, 20 in summer 10 in winter.

Thanks again,
Matt