Falling Oil Pressure

[PJH]

Prior to my car's head gasket failure 2 weeks ago the oil pressure was always on 3, unless the temp was high. But would always be 3 at 1,500 rpm or higher.
Since head gasket change the oil pressure is about 2.8 when cold, falling to 2.0 after 15 miles.

Why ?

Also, engine temp is now about 88-90 instead of the usual 82-84.

 

[DITTRICH]

I posted a similar question about W124 oil pressure a few weeks ago. The answers that came back explained that...
1 Oil pressure sensors on W124's can be iffy and may need to be changed.
2 When cold, on starting, the oil pressure goes up to 3 . As the engine temperature rises, the oil heats up and it's viscosity decreases, so its easier for the oil to be pumped about. After my engine gets to 85 degrees, on idle at 700rpm, the pressure is 2 . Merely blipping the accelerator to 1,300rpm makes the oil pressure rise to 3 .
In your case, I would assume the oil pressure sensor is okay and the behaviour of your oil pressure gauge seems to be okay.
Les

 

[PJH]

Thanks DITTRICH, Lord Walker aka "Preston Mercedes Support" has given my some other pointers as well that relate to adjustments that should have been done after the head gasket job.
Currently the oil pressure is on 2 at 2,000+ rpm when engine is hot.

 

[jgevers]

Hi,

If the engine has been very hot when the gasket blew, I would expect that the oil pressure sender has suffered a bit. Either fit a new one or get a garage to check the actual oil pressure.

If it turns out that the pressure sensor is ok and the actual oil pressure is low it could be a variety of things. Firstly I would check the oil pump and oil pressure relief valve. The items can be affected if the engine has overheated.

If you had a gasket failure that allowed the coolant into the engine oil, it could have affected the main crank bearings. This is worst case scenario.

regards,

Job

 

[DITTRICH]

Currently the oil pressure is on 2 at 2,000+ rpm when engine is hot.

Ah! I didn't understand from the post that your oil pressure was ALWAYS at 2 after the engine warmed up. That does qualify as a problem.
Les

 

[PJH]

Just found the water expansion tank is FULL, and there is oil in the water....

 

[jgevers]

Just found the water expansion tank is FULL, and there is oil in the water....

Oops,

It sounds like gasket has failed again. Check whether head had been checked for flatness and/or skimmed. If head was definately flat, I would get it pressure tested for cracks.

regards,

Job

 

[Ian B Walker]

Back to see the Muppets that fixed it then. Insist on a full examination and cure, seeing as you paid out loads of dosh.

 

[PJH]

I have been told by the garage that the problem is a perforated oil cooler.
As the oil pressure is greater than the water pressure the oil was being pumped into the cooling system.
Replacement £129. Apparently there are lots in store in Milton Keynes.

 

[Ian B Walker]

Oil cooler?????? the only oil cooler I can think of is the one that cools the gearbox oil, its part of the rad. I may be mistaken though. (check your ATF)

 

[PJH]

The mechanic was taking the car for a run when the oil pressure started to drop again, as originally described. He thinks that there must be a crack somewhere that is opening up when the engine get hot.
The head is coming off again.

 

[PJH]

It is now 4 weeks since my car went back to the garage.
The head has been skimmed and re-fitted. Having run the engine for some time, they
discovered that oil is once again getting into the coolant. Same as 4 weeks ago.
I now suspect it has a cracked block.

 

[PAUL R]

It is now 4 weeks since my car went back to the garage.
The head has been skimmed and re-fitted. Having run the engine for some time, they
discovered that oil is once again getting into the coolant. Same as 4 weeks ago.
I now suspect it has a cracked block.

Ho No! as they say when it rains, it pours

 

[PJH]

Ho No! as they say when it rains, it pours

Yes, and it's been p--ing down rather a lot lately.

 

[PJH]

Update:- engine out and sent to www.creweengines.co.uk to be re-built.

Edit 26th August :- Got my car back yesterday after 8 weeks off road.
It has been fitted with a replacement engine.