P38A Head gasket advice needed

I'm starting to suspect the water pump is bad, based on other forum posts I find.

Bit strange as I didn't have the overheating problem before changing the coolant, but also didn't run the engine long.

Any idea how to test the water pump if there is an air lock?

Are you sure the radiator bleed pipe is clear? The small one from the radiator to the neck of the expansion bottle.. take it off the radiator, take the cap off and blow down the pipe r reconnect
With the engine running at 2000rpm you should get a good flow of water returning if you look into the neck. It should still dribble at idle

kermit_rr said:

Are you sure the radiator bleed pipe is clear? The small one from the radiator to the neck of the expansion bottle.. take it off the radiator, take the cap off and blow down the pipe r reconnect
With the engine running at 2000rpm you should get a good flow of water returning if you look into the neck. It should still dribble at idle

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Yeah I've blown that out multiple times.

Will I get a stream of coolant through that pipe if there's an airlock?

If the top hose has coolant in it then yes.
If it's empty then you need to burp it.
I've found if it's really stubborn you're best draining and starting again. Fill it slowly, a small jug can help. Listen out and you'll start to hear it glug, when it does this, finger over the bleed hole and squeeze the top hose a few times you'll hear it wheeze and the level drop. Fill some more, repeat

There's no flow going through the bleeding line back to the header tank. If I squeeze the top hose there's gurgling.

I'm going to replace the water pump even though I don't know if it's bad or not. It's not expensive and seems reasonably easy to do. The car has been sitting for 10 years so maybe it's a good idea anyways.

If you can feel water in the top hose then it should spill out when you take the bleed pipe off.
If it doesn't then you've a blockage, you should be able to poke something up there eg wire.
Some DIYers love to use bath sealer instead of gaskets, bits break off inside and cause problems like this. Ask me how i know
If it does then yes the pump might be bad. Metal ones can rust, plastic ones can break. Metal ones are still better

kermit_rr said:

If you can feel water in the top hose then it should spill out when you take the bleed pipe off.
If it doesn't then you've a blockage, you should be able to poke something up there eg wire.
Some DIYers love to use bath sealer instead of gaskets, bits break off inside and cause problems like this. Ask me how i know
If it does then yes the pump might be bad. Metal ones can rust, plastic ones can break. Metal ones are still better

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Bath (silicone) sealant - yep..!!! Makes its way round to the rad bleed pipe and blocks it at the header tank end.. steam results.

Solved it!!

Water pump was not damaged, was one with a brass pump wheel so I'm keeping it as a spare. Probably not necessary to have changed it. It was indeed glued in with loads of silicone/RTV. I don't think changing it was what solved my issue.

On recommendation of a friend I did not fill the system from the header tank. I disconnected the top radiator hose and filled both the block and the rad up from there. I think that's what solved it. Bit of bubbles after start up but nothing like before. Solid stream from the bleed pipe now. Top hose still gurgling slightly when I squeeze it but I think that will solve itself after a bit of running.

I think that's a top tip for all V8 owners: fill the coolant from the top rad hose and not from the header tank.

Also I managed to change the water pump including doing a thread insert while only losing about 1,5l of coolant. Hose clamping pliers are really something every DIY mechanic should get. I clamped up the top hose, the hose towards the pump, the hose towards the throttle body and 1 of the heater core hoses. By keeping the system airtight like this it didn't drain completely.

Reason I did this was because I had just replaced the coolant.

Thanks for the help and advice everyone!

Glad you got sorted but it really shouldn't be necessary to do that. O do wonder if you've got a blockage somewhere you've not found yet.
Be careful and keep an eye on the temp for a while

Not such a good outcome on my P38 cooling system - overheated when some silicone sealant (that invention of the devil) blocked up the rad bleed pipe at the header tank end. Blockage cleared and system refilled, but now it defo has exhaust gas in it.
The RELD blue dye test indicated gas, and the simple smell test confirms it.
Now I am trying to find a local garage that will replace the head gasket - not sure whether to get both done at the time - engine has done around 90k miles.
Just have to hope that the heads are not warped and there is no shifting of the liners... Fingers crossed.

Oh dear. Do you know how hot it got?
Do both, they don't last forever.
I hope the block is ok

kermit_rr said:

Oh dear. Do you know how hot it got?
Do both, they don't last forever.
I hope the block is ok

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The temp gauge shot up and red light came on, but it didn’t lose all its water - I think about 2-3 litres was dumped. No steam gushing either. Fingers crossed…!

IMO, you should do both head gaskets or you will be having the work done again to replace the second one.

P38 Monkey said:

Not such a good outcome on my P38 cooling system - overheated when some silicone sealant (that invention of the devil) blocked up the rad bleed pipe at the header tank end. Blockage cleared and system refilled, but now it defo has exhaust gas in it.
The RELD blue dye test indicated gas, and the simple smell test confirms it.
Now I am trying to find a local garage that will replace the head gasket - not sure whether to get both done at the time - engine has done around 90k miles.
Just have to hope that the heads are not warped and there is no shifting of the liners... Fingers crossed.

View attachment 295354

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Do both.

It isn't a bad job but it does take time, especially the exhaust bolts which tend to be seized,. especially the heat-shield ones. We ended up just chiselling them off and using exhaust wrap on reassembly.

Take one weekend to pull it apart and then check what you need for reassembly and order the parts. Put it back together the following weekend.

P38 Monkey said:

The temp gauge shot up and red light came on, but it didn’t lose all its water - I think about 2-3 litres was dumped. No steam gushing either. Fingers crossed…!

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fingers crossed indeed
i'd say upgrade to head studs while you're at it, but thats a lot of money if you find the block has already suffered

Forgot to mention, you can use an engineer's rule to check if the heads have warped but usually they're fine and the gasket has just blown near the back.

kermit_rr said:

Glad you got sorted but it really shouldn't be necessary to do that. O do wonder if you've got a blockage somewhere you've not found yet.
Be careful and keep an eye on the temp for a while

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Really would surprise me if there's a blockage because I flushed it out with tap water. I also blew it out with compressed air through the outlet of the heater core, quite thoroughly. (I changed coolant types). But I think that may have been the issue. I blew every last drop of coolant out, probably blowing air into parts which normally never really drain.

I will definitely keep a close eye on the temp guage! And I'll check coolant flow through the bleed pipe from time to time.

P38 Monkey said:

Not such a good outcome on my P38 cooling system - overheated when some silicone sealant (that invention of the devil) blocked up the rad bleed pipe at the header tank end. Blockage cleared and system refilled, but now it defo has exhaust gas in it.
The RELD blue dye test indicated gas, and the simple smell test confirms it.
Now I am trying to find a local garage that will replace the head gasket - not sure whether to get both done at the time - engine has done around 90k miles.
Just have to hope that the heads are not warped and there is no shifting of the liners... Fingers crossed.

View attachment 295354

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Oh my that doesn't sound fun.. Based on what I've heard the liners is something that is more likely to happen on high-mileage blocks. Of course this is hearsay so don't quote me on it...

Why not attempt the head gaskets yourself? It's a relatively easy engine to do it on because of the pushrod design. No messing about with timing etc.

HG arent hard to do, just take time. liners can randomly go at any point, or not, doesnt have to be high mileage thouh some will argue if they havent gone at 100,000 miles they'll never go (unless you overheat)

Yes, driving with overheat is what kills the liners but you'll hear the tick as it hits the block from the liner moving up and down with the piston. No tick then probably fine.

ar1g3 said:

Really would surprise me if there's a blockage because I flushed it out with tap water. I also blew it out with compressed air through the outlet of the heater core, quite thoroughly. (I changed coolant types). But I think that may have been the issue. I blew every last drop of coolant out, probably blowing air into parts which normally never really drain.

I will definitely keep a close eye on the temp guage! And I'll check coolant flow through the bleed pipe from time to time.

Oh my that doesn't sound fun.. Based on what I've heard the liners is something that is more likely to happen on high-mileage blocks. Of course this is hearsay so don't quote me on it...

Why not attempt the head gaskets yourself? It's a relatively easy engine to do it on because of the pushrod design. No messing about with timing etc.

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90k miles on the engine…
I am 76, so considerably more mileage than my P38. Garages seem less than keen to do it - I think they like servicing newer cars. Might well end up doing it.