High coolant pressure

[Roan 0]

My '96 VR6 has been with my mechanic for a few weeks now, getting all manner of stuff done (a mini-restoration to be honest). I've had the heater matrix replaced and the system flushed and am currently awaiting a new auxiliary water pump which was leaking. My mechnanic now tells me that the coolant pressure is off the scale after a run of about 15 miles and has ordered a new expansion tank cap hoping that will solve the problem. The car exhibits no other signs of problems (no mayo as far as I know and didn't notice any when I bought the car a few weeks ago nor any white smoke from the exhaust). Would this point to a possible headgasket failure anyway?

 

Could the fact that the auxiliary water pump is leaking be a contributing factor?

[Jon_vr6 1]

What about a yellow temp sensor thats on the thermostat housing might have given up the ghost, are the fans coming on

[robrado974 1]

need to check thermostat aswell ,if head gasket was gone it would be runnin rough and lumpy [oil n water mixin] .

[Jon_vr6 1]

need to check thermostat aswell ,if head gasket was gone it would be runnin rough and lumpy [oil n water mixin] .

 

Yep maybe air lock in the system top and bottom rad hoses should be warm

[Roan 0]

Thanks to you both for the suggestions - never thought about an air lock being the problem. I had considered a stuck-closed thermostat but as far as I know the car isn't running hot, just very pressurised once warmed up. I'll mention this tomorrow to my mechanic..

[davidwort 0]

tank cap will only be a problem if it's blowing out water at normal or below pressure, i.e. cap isn't holding enough pressure,

if the system is genuinely pressurising too high then I'd have thought it's more likely a headgasket problem?

Always worth measuring how much water goes into the engine when filling from completely drained, then you know if there's a lot of air in there.

In my experience a slow fill usually means no more than a cupful of coolant needs adding after the first full cycle, up to temp and fully cooled, the remaining bit of air comes out then.

[onzlouk 0]

 

Yep maybe air lock in the system top and bottom rad hoses should be warm

 

Almost definitely what he said ^^ I found out myself they can be a bas***d to bleed up.