P38A Pressure in Expansion Tank

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JOHN ELLIS

JOHN ELLIS

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Location
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Hi All,

I have a 4.6 V8 P38 Range Rover

I have noticed this morning that the coolant level looked a little low, so I took the expansion tank cap off and a lot of hissing occurred and the level come back to just under the max.

I was under the impression that a cold engine that had stood overnight should not be under any pressure?

The engine runs fine with and the temperature is fine.

Is this a sign of more coolant issues on the horizon.

Cheers

John
 
Get her up to temperature and stable. Release pressure (being darn careful not to scald yourself with escaping steam!). Put cap back on, see if it repressurises.

Or try the UV dye test. Just bung UV dye in the coolant and then wait a few days and shine a UV torch on the dipstick. Or get a sniff test kit.
 
I had this on the L322....turned out to be a recurring airlock caused by a stuck GB oil cooler stat.....it was stuck, the expansion tank hose ran through this - as coolant expanded when hot and engine running, as the coolant cooled and contracted, the coolant couldn't flow back into the system and so sat there in the tank....even after being left for 36+ hours, when you opened the cap, it would **** coolant everywhere until you opened the bleed screw and the airlock at the top of the rad could be expelled, then the level would return to normal.

My solution was a new GB oil cooler stat......

This sorted it for a while, then it kept happening again, I finally traced it down to a split heater matrix that as the coolant cooled and contracted would draw air into the system and cause a massive airlock.

Now I know the P38 doesn't have a GB oil cooler stat but the principle remains.....I would be checking all the hoses and pipes for blockages, and also don't discount the possibility of a minute split somewhere drawing air in.

Do you have a cooling system pressure testing kit?
 
Saint.V8 said:
I had this on the L322....turned out to be a recurring airlock caused by a stuck GB oil cooler stat.....it was stuck, the expansion tank hose ran through this - as coolant expanded when hot and engine running, as the coolant cooled and contracted, the coolant couldn't flow back into the system and so sat there in the tank....even after being left for 36+ hours, when you opened the cap, it would **** coolant everywhere until you opened the bleed screw and the airlock at the top of the rad could be expelled, then the level would return to normal.

My solution was a new GB oil cooler stat......

This sorted it for a while, then it kept happening again, I finally traced it down to a split heater matrix that as the coolant cooled and contracted would draw air into the system and cause a massive airlock.

Now I know the P38 doesn't have a GB oil cooler stat but the principle remains.....I would be checking all the hoses and pipes for blockages, and also don't discount the possibility of a minute split somewhere drawing air in.

Do you have a cooling system pressure testing kit?
Click to expand...

Yes I have a coolant pressure test kit also a exhaust gasses die for failed head gaskets, going to have another busy day tomorrow by the looks of it.
 
Seems like we have similar issues. Hope the sniff test shows ok. Also, check your expansion cap. Just noticed the lower rubber o ring on mine is missing so for £10 i'm changing it first to rule out.
 
martynv8 said:
Seems like we have similar issues. Hope the sniff test shows ok. Also, check your expansion cap. Just noticed the lower rubber o ring on mine is missing so for £10 i'm changing it first to rule out.
Click to expand...
With the amount of times my cap has been on and off it wouldn't shock me.

Thanks for the advice everyone, I will post my findings.

John
 
Well that was strange, before I set off home I checked the coolant level and to my surprise it was normal, so I thought I would check to see if there was any pressure in the exp tank and the coolant almost spilled over, so I got my syringe and got the coolant down to normal level, put the cap back on and drove home.

Got home and exp tank is almost empty.

So I have dug out my sniff test kit see picture attached which I got because I knew one day I would need it.

Only problem is, instructions say to insert into radiator access point, there isn't one as you can see from my picture.

Can I do this from the expansion tank instead?

I don't have much test fluid so I can't afford to screw this up.

I did have a good sniff when I took the exp tank cap off at work and it definitely had an aroma.

I'm just waiting for the engine to cool a bit before I attempt anything else.
 

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Well, the test was negative but with the return hose pumping coolant back into the expansion tank right near the top of the tank I'm pretty sure I was sucking coolant up into the test fluid, would this screw up the test?
 
If I take the expansion cap off the next day after driving iv still got pressure in the cooling system I would say its completely normal trust me I know iv done the head gaskets and chased coolant leaks for months at one point.

Its normal don't worry
 
biketeacherdave said:
If I take the expansion cap off the next day after driving iv still got pressure in the cooling system I would say its completely normal trust me I know iv done the head gaskets and chased coolant leaks for months at one point.

Its normal don't worry
Click to expand...

Crazy crazy behaviour, well I'm going to do the test again tomorrow (in day light), them I'm going to, put the coolant pressure test gauge on and run the engine up to temperature and see what the reading is, then I'll kill the engine and see what happens to the pressure.

See how it all behaves.
 
Saint.V8 said:
Your test is invalid, it must only suck in the gases from above the water in the ET.

Your original post say is hisses a lot......a small residual pressure is expected, a lot of hissing ins't normal.
Click to expand...

I'll run all the tests tomorrow and see what the readings are.

My biggest concern is if it is holding pressure like this will it eventually blow out of the expansion and overheat the engine. Worst case scenario and all that ☠️
 
Hi All,

Today I put the coolant pressure test kit on the expansion tank and ran the engine up to temperature, I also had the wife put some revs on up to 2500 rpm whilst the engine was at full running temperature.

Crazy thing is, when I shut down and went cold the coolant pressure dropped as normal.

Please see my video's that I uploaded to you tube.




Can anyone see any inconsistencies on the gauge if so please let me know.

But from my finding's today I honestly think I had an airlock in the system and that was causing the original pressure problem.

I have topped up the coolant to the max level mark and I will keep an eye on it and see what happens.

Thanks everyone for the helpful tips.

John
 
If the pump isn't always pumping or the stat is jamming I was thinking it might overheat and burp backwards and out. If it was intermittant then sometimes it would bak out and sometimes it would flow. But I'd expect you to see something on the needle.
 
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