P38A 4.6 Engine Refresh

P38Tom · Jan 9, 2020

Hi all,

Long time lurker, first time poster.

I bought a P38 a few months back for £850 to use for a bit of fun and workshop workhorse. I absolutely love the car and have already done a ton of work on improving it. It's a british racing green autobiography with a 4.6 Thor engine.

It now looks like the head gasket is gone (mayonnaise on oil cap) so will do that this weekend. My question is whether or not I should just do a slightly bigger job rebuilding the engine top and bottom end. It's done 192k miles so is very long in the tooth. I'm just concerned about opening a can of worms when I head gasket change might just let it rumble on for another 50k?

Thanks for reading!

DanClarke · Jan 9, 2020

If you pop the heads off and there is clear evidence that it was just a failed gasket and no cracks or slipped liners to be seen, maybe its a cheap way to more fun motoring?
Any ideas what the compression is like on the cylinders?
Doing the full job might take a while and cost a lot more.
Someone far more qualified will be along in a moment I am sure.

Henry_b · Jan 9, 2020

You say "workshop horse" how far does it drive after every run?

Is it losing coolant?

Might be condensation from lack of a proper run..

P38Tom · Jan 9, 2020

Henry_b said:
You say "workshop horse" how far does it drive after every run?

Is it losing coolant?

Might be condensation from lack of a proper run..

Hmmm, no it doesn't seem to be losing coolant which I guess would be contrary to a blown HG. I do often drive it for very short periods just to move it around or re-park it (London painful parking). Occasionally it gets longer drives to Salisbury plain or a pay and play.

Maybe worth just keeping an eye on the coolant level.

Datatek · Jan 9, 2020

Mayo might just be due to repeated short runs, especially if it never gets up to full working temperature.

P38Tom · Jan 9, 2020

DanClarke said:
If you pop the heads off and there is clear evidence that it was just a failed gasket and no cracks or slipped liners to be seen, maybe its a cheap way to more fun motoring?
Any ideas what the compression is like on the cylinders?
Doing the full job might take a while and cost a lot more.
Someone far more qualified will be along in a moment I am sure.

I'll do a compression test first and see what's what. Thanks!

Henry_b · Jan 9, 2020

P38Tom said:
Hmmm, no it doesn't seem to be losing coolant which I guess would be contrary to a blown HG. I do often drive it for very short periods just to move it around or re-park it (London painful parking). Occasionally it gets longer drives to Salisbury plain or a pay and play.

Maybe worth just keeping an eye on the coolant level.

Clean the cap out, maybe ever pull the rocker covers, clean 'em out and take her for a good run..

Ratae · Jan 9, 2020

Mayo in the oil filler cap IS NOT a surefire indicator of hgf.
If you are not losing any coolant then you don't have hgf - or any other cooling system leakage for that matter.
Burning a gallon of diesel or petrol produces as a byproduct a considerable quantity of water.
It appears as the steam & the liquid you see dripping out of the tailpipe.
Cars used for short journeys don't get hot enough to boil this water off & you will see the mayo & you'll go through exhausts faster than car used for long journeys as they will rot out from inside. Even more common at this time of year in cold weather.
I sometimes wonder how many car owners have had their trousers pulled down by unscrupulous garages for unnecessary work.

kermit_rr · Jan 9, 2020

Unless you're sure it's a recent thing, the mayo could have been in there for years, since the HG did actually fail

RangeRoller dt · Jan 9, 2020

You have any receipts with it?

norseman · Jan 9, 2020

Ratae said:
Burning a gallon of diesel or petrol produces as a byproduct a considerable quantity of water.

Roughly equal I believe.
ie burning one pound of any hydrocarbon fuel produces one pound of water (?)

Click to expand...

JJKM · Jan 10, 2020

Agree with all of this. Clean the cap, take for a good run then check again. Compression test for consistency across the cylinders and look for bubbles or pressure in the header tank. If you get none of these, rule HG failure out. Compression is likely to be lower than the book says but if it is consistent, you're probably good.

Henry_b · Jan 10, 2020

A 10% discrepancy between reading will warrant the heads pulled.

I doubt it's HG though..

Alpinejim · Jan 10, 2020

Possibly just worn rocker gaskets.

Grrrrrr · Jan 10, 2020

If it is a v8 and not leaking something somewhere then it must be the only one they ever made that way.

Turboman · Jan 10, 2020

Grrrrrr said:
If it is a v8 and not leaking something somewhere then it must be the only one they ever made that way.

Must have run out of oil!

JJKM · Jan 10, 2020

Grrrrrr said:
If it is a v8 and not leaking something somewhere then it must be the only one they ever made that way.

It's not just V8, if it's made by LR then it leaks something!

kermit_rr · Jan 10, 2020

JJKM said:
It's not just V8, if it's made by LR then it leaks something!

Usually your wallet that leaks

Henry_b · Jan 10, 2020

Grrrrrr said:
If it is a v8 and not leaking something somewhere then it must be the only one they ever made that way.

It's not leaking oil..

It's sweating power!!

Unlike the diseasel

Grrrrrr · Jan 10, 2020

Henry_b said:
It's not leaking oil..

It's sweating power!!

Unlike the diseasel

The turbo-wheezle doesn't leak anything!

P38A 4.6 Engine Refresh

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