cljcars · Mar 29, 2022

I reckon I have a combustion gas leaking into the coolant. Coolant was slowly dissapearing and there are small bubbles in the expansion tank. This is a right pain, job I can do. But didn't need it now.
What are the chances of this being a cracked head or block? Anyone heard off blocks heads cracking on these?

Datatek · Mar 30, 2022

Have you done a gas test on the coolant?

biketeacherdave · Mar 30, 2022

Head gasket more common

cljcars · Mar 31, 2022

Datatek said:
Have you done a gas test on the coolant?

I have done. It passed the idle test, however I don't think there is enough for it to show up. I am going to repeat the test again at some point.
I cannot see how I can still be getting bubbles in the expansion tank If there was no head gasket issue or crack somewhere.??????

cljcars · Mar 31, 2022

biketeacherdave said:
Head gasket more common

I have googled and cannot find anything on 4.2 SCs with cracks found, so hoping it's uncommon.

tomcat59alan · Mar 31, 2022

Is this the one that you cocked up the wheel arches with body filler and bent metal?

Grrrrrr · Mar 31, 2022

On the Range Rover the Jag engine has been known to leak where it passes round the back somewhere. From what @Henry_b says it normally pumps out PDQ though.

tomcat59alan · Mar 31, 2022

Grrrrrr said:
On the Range Rover the Jag engine has been known to leak where it passes round the back somewhere. From what @Henry_b says it normally pumps out PDQ though.

There's a hose that runs under the supercharger in the valley which is prone to failure,it's a bastard to do on the XJR but not as bad on the RR.

badfluffy · Mar 31, 2022

if its the same as the xk8 there's a pipe at the back lovingly called the octopus, nightmare to change and will let air in if not fitted properly

Datatek · Mar 31, 2022

cljcars said:
I have done. It passed the idle test, however I don't think there is enough for it to show up. I am going to repeat the test again at some point.
I cannot see how I can still be getting bubbles in the expansion tank If there was no head gasket issue or crack somewhere.??????

I think you are jumping to conclusions based on the P38 V8.

Henry_b · Mar 31, 2022

Valley pipe which runs under the supercharger is a common failure point on the AJV8..

Never heard of HG let alone head crack on the Jag engine, a very robust unit it is.

cljcars · Apr 1, 2022

tomcat59alan said:
Is this the one that you cocked up the wheel arches with body filler and bent metal?

Eh????. Think might have me confused with somebody else.

cljcars · Apr 1, 2022

Datatek said:
I think you are jumping to conclusions based on the P38 V8.

Yep, paranoid. Been there and done the tophat on the 4.6.
There is definitely an issue somewhere because it starts lumpy sometimes as if it hydro locking. I will pull the plugs and see if it's washing the top of a piston.

cljcars · Apr 1, 2022

Henry_b said:
Valley pipe which runs under the supercharger is a common failure point on the AJV8..

Never heard of HG let alone head crack on the Jag engine, a very robust unit it is.

Cheers, I can only see the odd head gasket issue on Jag forums, plus a YouTube head gasket failure. Been through the history file and can see lambda's have been changed..... raises an eyebrow.

kermit_rr · Apr 1, 2022

Hydrolock is just that, engine locks up.
If it starts then it's not hydro locked

tomcat59alan · Apr 1, 2022

cljcars said:
Eh????. Think might have me confused with somebody else.

You may be right I'm easily confused these days.

cljcars · Apr 1, 2022

tomcat59alan said:
You may be right I'm easily confused these days.

It has has some filler though, so not far off.

cljcars · Apr 1, 2022

kermit_rr said:
Hydrolock is just that, engine locks up.
If it starts then it's not hydro locked

OK, Yep correct. Hydrolock was not the right description. It hesitates to turn over as if it has higher compression on one of the cylinders because cylinder volume has been reduced with an incompressible liquid (coolant) but not completely filling the cylinder. So it causes a hesitation rather than hydrolocking.........

tomcat59alan · Apr 1, 2022

cljcars said:
OK, Yep correct. Hydrolock was not the right description. It hesitates to turn over as if it has higher compression on one of the cylinders because cylinder volume has been reduced with an incompressible liquid (coolant) but not completely filling the cylinder. So it causes a hesitation rather than hydrolocking.........

Pull the plugs and see which are steamed.

Gord Wedman · Apr 4, 2022

tomcat59alan said:
Pull the plugs and see which are steamed.

If the plugs are out you might as well do a compression test. Should tell you if a head gasket is gone.

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