P38A Diesel Head Gasket Replacement

Afternoon All,

I have spent some time reading various threads on replacing the head gasket on the 2.5TD and there seems to be some debate that it is not worth doing on such an older car, on the other hand, if correct procedure is followed then it is a fairly ok to do just time consuming.

Mine has done 178,000 miles, weekend car and head gasket has been determined by mechanic as cause of overheating at speed, exhaust fumes in the coolant, rock hard pipes and sniff test done 3 times same result. Fan, rad, thermostat and pump all changed.

I like working on the car changing all of the above and other bits like props and diff etc so I would like to change it but would like some advice on the best procedure and tips anyone can offer? Is it worth refurbing the valves etc?

My main nervousness is the timing chain and getting this wrong. I have the RAVE manual and read the procedure but be keen to hear everyone's experience and views?

It is probably not worth it on a car with this mileage and age (95 plate) but it is a project car so I wouldn't lose any value due to condition and would be a good learning curve.

Thanks.

Its straightforward to do ,take your time you need the cam holder and pin and chain slackener (for want of a better title). The head is heavy to lift on and off (I used an engine crane)no major difficulties. I removed exhaust to get turbo off and I cut the heat shield and screwed it back together with plates and screws

Sorry to say thet HGF is unusual on the M51, a cracked head is much more common.
If the car is in good condition, it's certainly worth doing IMO. 178K is not a lot, there are many on well over 200K.

Tools will cost about £120 off the Bay unless you have them.

There's a debate as to whether the head can handle a tiny skim or not but either way best have it pressure tested before refitting.

Grrrrrr said:

Tools will cost about £120 off the Bay unless you have them.

There's a debate as to whether the head can handle a tiny skim or not but either way best have it pressure tested before refitting.

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BMW say the head cannot be skimmed. It's weak to start with, skimming it is asking for trouble.
New heads are available for €900, used ones for a lot less.

thanks for the responses, maybe it has a cracked head instead of a head gasket, suppose I wont know until I take the head off.

I mean the car is good for its age, it is solid, just a few rust areas and saggy headlining usual stuff.

I can keep the car running on just topping coolant up but gets frustrating when at high speed (above 70) it will overheat and have to let it cool down and top up, generally if it is driven at 65mph it behaves itself.

It is a weekend car and rarely goes on the motorway I think it is more of getting better knowledge of cars as a home mechanic.

In terms of the tools needed do I just order ones shown on RAVE manual?

thanks all again.

Did you make sure the rad has the baffle fitted in the top

If you do the head it will last long time. Chains, tensioners, sprockets all worth doing same time. Valves and seals if you can while you are there but not a must. It will benefit a lot from a strip and clean down - mine has and I’ve not been that invasive yet. Careful with no4 injector wire/sensor they get weak with age/heat and will cost to replace. You will need to use ‘new engine’ settings.

The alloy heads on these are not suitable for skimming IMO. Doesn’t mean it can’t be done but not applicable to your situation as it’s probably cracking - you will see when it’s off. Head is cheap enough if you shop about

If the overheat is not constant i would have thought a cracked head was the culprit. Had one a while ago that would drive around normally for up to an hour then blow all the coolant out. Head had a minute crack between the valves on number two.

ok cheers guys I might take the plunge and remove the head only way I will know as it is overheating a lot quicker than it is use to so whether it be head gasket or cracked head.

wammers said:

If the overheat is not constant i would have thought a cracked head was the culprit. Had one a while ago that would drive around normally for up to an hour then blow all the coolant out. Head had a minute crack between the valves on number two.

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Much like the one I scrapped, it would tootal about at low speed, but try to climb the hill out of my place and it would blow the water out.

Lukas018 said:

ok cheers guys I might take the plunge and remove the head only way I will know as it is overheating a lot quicker than it is use to so whether it be head gasket or cracked head.

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Very unlikely to be head gasket overheat would be constant.

From what i understand the M51 will turn it's head into margarine if overheated

I'd give the heat a good going over, pressure test etc before refitting.

A member did his HG but still had the symptoms, turns out the head was Junk.

They can crack pretty bad but usually tiny tiny cracks only really visible with a dye, I have been led to believe. They can cook good few times with no head problems, but not something to be ignored.

I will have too have a think about it.
I looked at the rad installed it is the aluminium upgrade version it was replaced a month before I bought it 2 years ago, I wouldn't suspect it is faulty but I ran the car up to temp, felt the top of the rad, boiling hot, bottom of the rad cool, but you would expect it to be with the fan operating. But some suggestions could be baffle is not working properly. I could buy another rad but is it worth it if the head is cracked which it looks like it is leaning towards?

What do you guys reckon is best?

Thanks,

Do the marble test on the rad, take it out put marble in one end and see if it will roll out the other if i does then no baffle in top and new rad needed anyway even if the head is cracked and replaced

ok mate will do cheers.

Lukas018 said:

I will have too have a think about it.
I looked at the rad installed it is the aluminium upgrade version it was replaced a month before I bought it 2 years ago, I wouldn't suspect it is faulty but I ran the car up to temp, felt the top of the rad, boiling hot, bottom of the rad cool, but you would expect it to be with the fan operating. But some suggestions could be baffle is not working properly. I could buy another rad but is it worth it if the head is cracked which it looks like it is leaning towards?

What do you guys reckon is best?

Thanks,

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The RAD should be hot all over, if the top is hot but the bottom is cool, it could be that the baffle has partly failed.
If the water pump has been replaced, there is also a chance that the original plastic one broke up and there are still bits in the engine restricting flow.

There is a cheap enough uv dye you can buy shows if combustion gases are present in Coolant system then you will know for sure if head has leak without taking everything off.

I would marble test too as this is common for cheap rads even after 2yrs and I’m guessing a marble costs little to check for sure

Also worth mention if your ancillary belt or associated parts are iffy your pump won’t turn effectively

Morning All,

I did buy a UV dye for the diesel leak but didn't have to use as found cause of the leak so I could use that. Done a sniff gas on the coolant and showed exhaust gases in coolant but I don't think these can ever be 100% reliable.

The water pump seized so I renewed that with new one and new belt etc.

I will do the marble test see how get on with that first as this wont help regardless if got a cracked head or gasket.

If the rad is bust am I better off buying an original rad as someone told me the aluminium ones were supposed to be better at cooling?

Thanks,