P38A Head Gasket Probably Blown - Advice

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Montyjohn

Montyjohn

Well-Known Member
Posts
246
Location
UK
Ok, so I think my head gasket on my MY2000 P38 4.0 V8 has gone. :(

I've had the car about a year, and in that time, the temp needle has never gone beyond half way.
I noticed about 2 weeks ago my expansion tank was almost empty. I assumed I just hadn't been checking it, so topped it up and thought nothing of it.
Then yesterday, coming home from my 5 mile commute, temp goes off the scale.
As I was only a mile from home, I let it cool, then limped home.
The temperature did creep up on this last mile, but then suddenly sprang back to half way.
At this point I thought it might be a dodgy sensor or just an air lock from a hose leak.
Anyway, when I got home, after a bit of cooling, removed the expansion cap, ran the car, and it bubbled so much the header tank spilt over.
My sniff test arrived today, and it's bad news. It went form blue to green (albeit very slowly). Took about 10 minutes to change colour.
Do these kits ever give false positives?

So what next.
According to the history, engine was re-built in 2015 with top hat liners with Tuners.
Assuming the history is accurate I'm ruling out an issue with the liners.
I'm using the car as a daily, and really can't afford the down time right now.
I'd love to pull the engine anyway, as it's loosing a lot of oil via the rear main seal, but I just don't have the time now, and as it would be my first V8 removal, I probably want at least 2 or 3 weekends to get the job done.
I could do the head in-situ and worry about the seal another year, but that seems wasteful.

Another option is k-seal to buy me some time until next summer. Wife is a teacher so we only need one car in the summer holidays. Same for Christmas, but I'd be doing this job on my driveway.

If this works, I may treat myself to a 4.6 crank and do a full re-built :) (I need a silver lining)

What would you do?
 
The fluid will naturally change colours over time as it reacts with the atmosphere. It should change more or less instantly if you bubble gases though it.
You can hear a slipped liner
My advice, don't put 'stop leak' in the coolant, it's bad news, at least on the narrow channels/pipes on a p38
 
I just had a similar issue and my P38 is in for head gasket(s) or liners or all the above. The RELD dye went from blue to yellow in less than a minute. Check the radiator bleed hose for a blockage at the header tank end.
 
I would change the coolant and back flush the rad. Defo no k seal. Chances are not high, but cd just be the coolant aystem misbehaving....quicker than doing the HG first off, and you can reuse the new coolant if it turns out to be the HG.
Did the overheat happen at low speed?
 
All k seal does is fill your rad and expansion tank with copper flakes.

If it has blown a gasket, it will of blown from the fire ring of either cylinder 8 2 7 or 1 in to the water jackets at the front/back of the block

Headgasket job isn't that difficult with the motor in the car, hardest part is getting the exhaust heatshields off ;)

As for steelseal save yourself half and buy water glass solution which is the primary ingredient in Steel seal but less than half the price. :)
 
P38 Monkey said:
I just had a similar issue and my P38 is in for head gasket(s) or liners or all the above. The RELD dye went from blue to yellow in less than a minute. Check the radiator bleed hose for a blockage at the header tank end.
Click to expand...
I checked this the other day and it was clear.
 
romanrob said:
I would change the coolant and back flush the rad. Defo no k seal. Chances are not high, but cd just be the coolant aystem misbehaving....quicker than doing the HG first off, and you can reuse the new coolant if it turns out to be the HG.
Did the overheat happen at low speed?
Click to expand...
Yes it was low speed. Probably 25mph up a slight hill (a lot of 20mph zones around me).
It was also only about half a mile from a 5 minute stop where I picked up my kid form nursery, so the engine shouldn't have been that hot to start with (unless it overheated on the way to nursery and I didn't notice, I don't think this is the case however)
 
kermit_rr said:
My advice, don't put 'stop leak' in the coolant, it's bad news, at least on the narrow channels/pipes on a p38
Click to expand...
The steel seal stuff that others have mentioned has a similar consistency to water, and only cures if exposed to hot gases, so if it gets into narrow passages it shouldn't react or cause any blockages.

I've got a vacuum and pressure testing kit arriving today, so I'm going to see if I can find any external leaks, and then bleed it by vacuum if it holds pressure and see how I get on.

Might also try the sniff test again with the engine already hot(ish) to see if it reacts quicker.
 
Montyjohn said:
I checked this the other day and it was clear.
Click to expand...
I had an intermittent blockage in the top of the radiator that would randomly stop the flow and cause problems.
Eventually plucked a string of silicon bath sealer out of the orifice that has broken off elsewhere. PO had used it to seal the water pump.
I'd previously had the radiator off to flush it, thoroughly i might add!! That failed to remove it.
Not saying this is your problem, just that things aren't always as they seem.. for anyone reading this thread in the future.
 
Last edited:
kermit_rr said:
I had an intermittent blockage in the top of the radiator that would randomly stop the flow and cause problems.
Eventually plucked a strong of silicon bath sealer out of the orifice that has broken off elsewhere. PO had used it to seal the water pump.
I'd previously had the radiator off to flush it, thoroughly i might add!! That failed to remove it.
Not saying this is your problem, just that things aren't always as they seem.. for anyone reading this thread in the future.
Click to expand...
That’s exactly what happened to my 4.0….
Blockage debris.jpg
 
Montyjohn said:
The steel seal stuff that others have mentioned has a similar consistency to water, and only cures if exposed to hot gases, so if it gets into narrow passages it shouldn't react or cause any blockages.

I've got a vacuum and pressure testing kit arriving today, so I'm going to see if I can find any external leaks, and then bleed it by vacuum if it holds pressure and see how I get on.

Might also try the sniff test again with the engine already hot(ish) to see if it reacts quicker.
Click to expand...
I experienced huge issues bleeding the coolant initially, but once i got the radiator and throttle body heat exchanger clear it was really quite easy. By that time i knew all the tricks too, i think they've all been mentioned on here
 
kermit_rr said:
I experienced huge issues bleeding the coolant initially, but once i got the radiator and throttle body heat exchanger clear it was really quite easy. By that time i knew all the tricks too, i think they've all been mentioned on here
Click to expand...
I'd also add, if you have major difficulty then there is a problem 'somewhere'.
The fact the thermostat doesn't have a bleed hole in it is not an issue. Warm the engine with the cap off then let it cool down fully and top up, job done
 
Montyjohn said:
This may be true, but if I do have the heads off, I was as well go a step further and get the rear main seal done. Thanks.
Click to expand...

No. Massive difference. Heads: first time call it a weekend to pull off, order all bits during the week and the next weekend to put together. Engine out is a long weekend just to get it out and a bit of a saga to be honest. Even finding a suitable engine crane. The rear seal can be done by removing the gearbox which is a mini saga and has its own dangers - the torque converter dropping forward so the oil pump drive disengages.
 
Grrrrrr said:
No. Massive difference. Heads: first time call it a weekend to pull off, order all bits during the week and the next weekend to put together. Engine out is a long weekend just to get it out and a bit of a saga to be honest. Even finding a suitable engine crane. The rear seal can be done by removing the gearbox which is a mini saga and has its own dangers - the torque converter dropping forward so the oil pump drive disengages.
Click to expand...
Had the box off a couple of times on my V8 automatic classic. First time to do the rear crank seal.
The assembled gearbox & transfer box are a big heavy & awkward lump.
I made the adapter plate in the workshop manual & fitted to a suitable trolley jack made it easier.

The TC will fall off it gets the slightest chance as there's nothing holding it in place & can be a PITA to get back on with the box level.
It's also very heavy & retains a lot of ATF which will spill all over the place once it falls off.
Guess how I know that.
It MUST be fitted to the gearbox AND to the correct depth before refitting otherwise you can still bolt everything up but the pump will be damaged & you get to take it all off again.
Best to come up with something to stop it slipping off at all. Small round inspection plate on the bottom of my bellhousing & I made a 'T' shaped bit of metal to stick up into the housing & hold the TC in place.
 
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