Thread: Coolant Pressure in my Defender Tdi300 - How to diagnose Head or Gasket?

See who chimes in,but for me i would be sending a PM to Dave,Blknight.aus,on here,he knows these inside out,and should give you some helpfull pointers.

Are you filling the tank right up or just to the halfway level.
I leave mine at halfway and it rises when hot and back again when cold.
If I fill it over that then it does overflow untill it finds its own level.

Originally Posted by 123rover50

Are you filling the tank right up or just to the halfway level.
I leave mine at halfway and it rises when hot and back again when cold.
If I fill it over that then it does overflow untill it finds its own level.

There's an internal marker in the reservoir that I fill to which is about half full. After driving it yesterday and leaving it all day today, when I got home I tried to remove the cap and there was still pressure there wanting to push out coolant.
I'm in the process to remove the head to see what the problem could possibly be...

best bet for home testing (and this is iffy) is to get the engine warmed up, remove the AC pump, run the engine again then pull the glow plugs and do a leakdown check with the fill plug in the thermostat housing removed IF you're lucky you'll get bubbles in the coolant there...

however.. Its a moot point If its the head gasket you have to pull the head.
IF you remove the head its best practice to crack and pressure test it while its off.

IF its the head, you have to remove the head and then you have to replace the head gasket.

If its bolt stretch letting the head lift a little you need to replace the head bolts, which means you have to replace the head gasket which means (refer to point 1).


Ive seen this a few times now and generally its the gasket on an older engine having just start to let go. when you clean down the combustion chambers as part of prep for doing the gasket if you notice a significant difference in the surface finish of the chamber compared to the others send it off for fluxing or other crack/porosity checking.

Also rans are crack in the cylinder wall.

Dont forget your P gasket, waterpump, its gasket, and all the core plugs while you;re in there. A radiator flush and heater core flush is probably a good idea as well, Might as well check the vacutator just before you descale and de rust the coolant transfer piper for the heater....

thermostat opening test and its gaskets too. Best to get that in place and done before you put the head back on....

Oh, the block drain and if you have it a new o ring for the radiator drain.

Well... Here's a bit more of the unfolding story...


Removed the Head & inspected the Head and Head Gasket and with my limited experience, I could not see anything that stood out indicating the problem.... I then cycled the Pistons through and found what I think may be the issue. It looks like No3 Cylinder Wall may have a crack in it. It's different to the other 3 cylinder walls.(see attached photos)


This engine was rebuilt some 30>40k again with all new 20thou pistons; bearings; camshaft, etc


Number-3





Number-3



Number-2



Number-4



Gasket





HEAD

Originally Posted by Blknight.aus

best bet for home testing (and this is iffy) is to get the engine warmed up, remove the AC pump, run the engine again then pull the glow plugs and do a leakdown check with the fill plug in the thermostat housing removed IF you're lucky you'll get bubbles in the coolant there...

however.. Its a moot point If its the head gasket you have to pull the head.
IF you remove the head its best practice to crack and pressure test it while its off.

IF its the head, you have to remove the head and then you have to replace the head gasket.

If its bolt stretch letting the head lift a little you need to replace the head bolts, which means you have to replace the head gasket which means (refer to point 1).


Ive seen this a few times now and generally its the gasket on an older engine having just start to let go. when you clean down the combustion chambers as part of prep for doing the gasket if you notice a significant difference in the surface finish of the chamber compared to the others send it off for fluxing or other crack/porosity checking.

Also rans are crack in the cylinder wall.

Dont forget your P gasket, waterpump, its gasket, and all the core plugs while you;re in there. A radiator flush and heater core flush is probably a good idea as well, Might as well check the vacutator just before you descale and de rust the coolant transfer piper for the heater....

thermostat opening test and its gaskets too. Best to get that in place and done before you put the head back on....

Oh, the block drain and if you have it a new o ring for the radiator drain.

Any more info on this ?
Had the block tested ?

Originally Posted by dero

Any more info on this ?
Had the block tested ?

Took the Head and Gasket to a Cylinder Head & Engine specialist today for him to check it out. After looking at teh Head and gasket + the photos of No3 Bore, he's 90% sure that the Head Gasket & head is the cause of the issue. He reckons the bore marks are stain marks but just to be sure, he's given me this red dye spray to spray in and around No3 bore where the marks are and then leave for 24hrs, then wipe clean & spray a white powdery substance that will draw out the red dye should there be a crack there... So I'll find out tomorrow the result as to where there is a crack there or not...
The engine builder who has done multiple TDi blocks and has never seen them crack in that spot, so I'm hoping that its just a stain mark and I can fit a new head gasket and the newly skimmed head and all will be good...

FWIW, I agree with the specialist, I've seen plenty "stain marks" in bores, and that certainly looks like one.