P38A intermittent coolant pressure issue

kermit_rr · Sep 26, 2019

It's back, again. Too much pressure.
Fished another stringy bit of silicon 'bath sealer' out of the expansion tank again so I'm convinced that's the root cause. Intermittent blockages.. somewhere!!
I suppose the next job is to drain the block and do a full flush.. is that easier said than done? How do i flush for foreign objects that may or may not be causing an obstruction?

kermit_rr · Sep 27, 2019

Also, does anyone know if it's normal for the bottom of the radiator to be cold when the engine is running and at normal operating temp?
Ie. Can the radiator dump enough heat to go from 90c at the top to.. say 20c at the bottom? (Not measured)
I'm probably over thinking things here

Datatek · Sep 28, 2019

kermit_rr said:
Also, does anyone know if it's normal for the bottom of the radiator to be cold when the engine is running and at normal operating temp?
Ie. Can the radiator dump enough heat to go from 90c at the top to.. say 20c at the bottom? (Not measured)
I'm probably over thinking things here

Not normal on the diesel for sure. No idea about the V8 but doubt it's normal on that either. On the diesel it would suggest the baffle in the header has failed is is failing.

kermit_rr · Sep 28, 2019

Datatek said:
Not normal on the diesel for sure. No idea about the V8 but doubt it's normal on that either. On the diesel it would suggest the baffle in the header has failed is is failing.

Cheers, even though it doesn't overheat at idle or driving at any speed?
I think the radiator is coming off again anyways so I'll check it out

Datatek · Sep 28, 2019

kermit_rr said:
Cheers, even though it doesn't overheat at idle or driving at any speed?
I think the radiator is coming off again anyways so I'll check it out

The bottom will be cooler than the top, but never cold. Maybe your 20C is a bit hotter than that.

kermit_rr · Sep 28, 2019

I've taken the stat off today, blown through all the smaller hoses/tubes and refilled, everything seems clear and refilled very easily. Fingers crossed!

RangeRoller dt · Sep 28, 2019

As I’ve said before there’s something clogging it. Pretty much all new

kermit_rr · Sep 28, 2019

Doing my best to de-clog!! Not sure what else to do though

RangeRoller dt · Sep 28, 2019

Just got wait for it break down to sludge and find it’s way to somewhere you can get to it? Atleast if it was plastic impeller (my first thought) it would’ve lodged.

Regular changes all you can do? Hope it sorts itself out for you

RangeRoller dt · Sep 28, 2019

Atleast you are now well versed in p38 cooling

kermit_rr · Sep 29, 2019

RangeRoller dt said:
Atleast you are now well versed in p38 cooling

Haha yes sadly true! Not sure silicone will break down that much though, just find its way through eventually to somewhere i can find it!
This last time I've not actually found anything though so put it back together in the same state apparently.
Will take it out today and see if it's any better

kermit_rr · Sep 29, 2019

2 minutes down the road and discovered the manifold o ring gives up, resulting airlock puts landy back on the naughty step

kermit_rr · Oct 9, 2019

Still on going... Aaargh!!
Back to basics, expansion cap off, run up to 90c, get all the air out,, no more bubbles coming through into the expansion tank.. switch off and allow to cool
Go for a drive the next day and we're back to square one!! Once it gets up to 90, the pressure starts building!!
Pretty sure there's no coolant leaks now and the lpg is totally disconnected.
Tested for hydrocarbons in the expansion tank again, negative result but not much to test when there's no bubbles!!
I'm missing something really obvious here

wammers · Oct 9, 2019

kermit_rr said:
Still on going... Aaargh!!
Back to basics, expansion cap off, run up to 90c, get all the air out,, no more bubbles coming through into the expansion tank.. switch off and allow to cool
Go for a drive the next day and we're back to square one!! Once it gets up to 90, the pressure starts building!!
Pretty sure there's no coolant leaks now and the lpg is totally disconnected.
Tested for hydrocarbons in the expansion tank again, negative result but not much to test when there's no bubbles!!
I'm missing something really obvious here

If you have bubbles entering the header tank. It is either combustion gas leaking into the coolant or LPG leaking into the coolant.

kermit_rr · Oct 9, 2019

When it over pressures, it's either a result or consequence of air in the system.
Once is got that out with the cap off and at running temp, there was no further bubbles

RangeRoller dt · Oct 9, 2019

If it’s leaking air can get in, this could be coolant sensor washers missing to holes/untight bung in the rad. Could be something simple like putting stat in wrong way by accident

Could be a blockage causing it to pressure up - more of that gunk - but that shouldn’t cause gas in header? Every time you work on coolant system you find bit more then it behaves while. There can only be a finite amount in there, try blowing it out like you did before?

wammers · Oct 9, 2019

kermit_rr said:
When it over pressures, it's either a result or consequence of air in the system.
Once is got that out with the cap off and at running temp, there was no further bubbles

You need someone with a static test rig. It is over pressuring from somewhere. The previously mentioned are the only things that can cause that. Ambient air cannot be drawn it is not possible.

kermit_rr · Oct 9, 2019

What do you mean by a static test rig? I have a pump and dial the screws in place of the cap, i pump it up and it holds pressure.. or do you mean something else?

wammers · Oct 9, 2019

kermit_rr said:
What do you mean by a static test rig? I have a pump and dial the screws in place of the cap, i pump it up and it holds pressure.. or do you mean something else?

A test rig can be used in two ways. As you state and fit but do not pressurise and run engine. Engine should run with coolant at around 5 to 7 PSI when warm at idle. If it goes off scale you definitely have a leak in either the head gaskets or the LPG heater.

kermit_rr · Oct 9, 2019

FINALLY found it!! Ran it up to temp again, no issue up until 94c. Only at that point did i see exhaust gases

Why on earth would it be ok when it's cooler? No idea but not happy and not sure what to do next.
Is the p38 scrap/parts?

P38A intermittent coolant pressure issue

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