P38 Manifold / Head Gasket

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g15ost

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Hi All. I have a 1997 4.0 P38. It has developed a noise which I initially assumed was the exhaust manifold (drivers side) blowing. I removed and inspected the manifold and found no obvious faults so replaced with new LR gaskets. Still making blowing noise. I then replaced manifold. Still making the same noise.

If I stick my hand beneath the manifold (without the heatshields fitted) I can feel air blowing onto it.

I removed plug cap 7 while it was running and the noise got a little better so I ran a compression test and that same cylinder was reading about 100psi (the rest were 135-149psi).

No loss of oil or water. No running problems. Drives fine.

Im guessing Head Gasket. Would anyone else agree? Have also been told it could be a valve problem but id imagine to have other symptoms like running problems or backfiring if it was a valve.

Basically im wandering if this has occurred to anyone else and / or how common an issue it is.

Any help would be much appreciated before I rip the head off!

Thanks!!!
 
Weak point on P38 manifolds, strangely more so on the r.h. (Drivers side) is weld fractures.
There is always the possibility that the replacement one was also cracked.

Futhermore, the manifold gaskets must be fitted correctly, it's easy to orientate them the wrong way round.
 
Hi mate. Thanks for the quick reply. Im pretty happy its Not a manifold fault. I could be wrong but from the fact i can feel the air leaking beneath the manifold suggests its coming from elsewhere.

If it helps narrow it down the noise is more of an air chugging or sucking noise when the car idles or is turned off.
 
Does it sound like pfft pfft pfft pfft... Etc... Thats exactly what i had only four weeks ago. turned out to be a half inch hole in thr drivers side head gasket. i thought it was cracked manifold originally, then searched online and found a video which sounded identical, then knew it was hg. Search my recent posts for the video, see if it sounds the same, i suspect it is. also search my recents, cos head gaskets aren't nearly as bad a job as i thought!!
 
P38_love/hatething said:
Does it sound like pfft pfft pfft pfft... Etc... Thats exactly what i had only four weeks ago. turned out to be a half inch hole in thr drivers side head gasket. i thought it was cracked manifold originally, then searched online and found a video which sounded identical, then knew it was hg. Search my recent posts for the video, see if it sounds the same, i suspect it is. also search my recents, cos head gaskets aren't nearly as bad a job as i thought!!
Click to expand...

Yeah. If you go on you tube and search range rover manifold theres a guy with a 4.6 posted a video with his making an identical noise that he said was hg. could you have a listen and let me know if that was the same noise as yours. Did you have any running issues or just the damn noise?

Many Thanks. Phill
 
Thats the exact video/noise, no change in perf. Just noise. Its compression leakage from head gasket blowing directly out side of block/head. read my recent posts, gaskets aren't too bad to do, i'm amazed garages won't take them on. If you eere in n.irelanf i'd offer a hand!!
 
P38_love/hatething said:
Thats the exact video/noise, no change in perf. Just noise. Its compression leakage from head gasket blowing directly out side of block/head. read my recent posts, gaskets aren't too bad to do, i'm amazed garages won't take them on. If you eere in n.irelanf i'd offer a hand!!
Click to expand...

Thanks. I thought it was the head gasket but needed somone to agree with me. I used to be a mechanic for mercedes so have some experience with V8's. Do you know what the torque settings are for the head bolts? I have a copy of the manual but it states its for cylinder heads from 99MY.

It says they are - 20nm followed by 90deg followed by a further 90deg. Is this the same for a 1997 model?
 
I'm not sure if it's exactly the same, mine's a 2000, but i can't see it being much different. it'll be in RAVE. download it if you haven't already, its great. other than that, it'll be a piece of **** if you are used to v8's. Just get a good impact socket, 16mm, for the head bolts and it'll be grand. i'm handy with spanners but it was the biggest job i've undertaken, on the nicest and most expensive lump i've owned!!
 
Exact same with mine and it was the head gasket. You will find the other side will have the same. Its best to do both at the same time as all the kit has to come off to do one, so do the other one at the same time. You will shear some bolts getting all of it off, thats a fact , so put together with some copper grease in case it goes again.
As its all off I'm putting in new idle pullies and water pump to ensure the cheap bits dont fail and cause the heads to go again as its a long slog stripping the top off
 
Heads off! As predicted there was a half inch piece of gasket missing from the 3rd cylinder (that was the one that read lower in the compression test). Have sent head to be skimmed and ordered gasket kit / new bolts so if all goes according to plan then ill be putting it back together wed morning.

Thanks for all your input on this and special thanks to love/hatething for the video that finally confirmed my theory on it being the gasket in the first place.

Good Times!
 
Good times indeed!! Nothing like that moment when the head comes off and the problem reveals itself clear as crystal... Makes it all worth it!! Your heads came off easier than mine them, although a better dtocked garage would have been better!! Good luck with the rest and happy times turning it over again!
 
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