Well, I'm starting to lose my sense of humour now, come to work all good, pulled into gas station to gas up on way home as I start the engine needle shoots up to red then settles back to normal, so I've pulled over and coolant level is really low, I've loosened the cap and sure enough coolant rises to max level.

After Saturdays test I'm wondering if the expansion cap is knackered and not releasing pressure as it should.
 
Will let you know if new cap sorts out my very similar issue - was hoping it would arrive today but hopefully tomorrow.
 
Just had a look at the cap, the seals seem ok, now from what I read on google there is supposed to be a spring that compresses to release pressure, I can't compress the spring down by hand but since I got home and removed the cap I seem to have lost a load of coolant (see picture).

Yet there are no visible leaks outside and the oil is fine with no milky stuff under the oil filler cap.
 

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I agree that the pressures look ok, but . . . .
  1. How hot was the engine, and how long was it running ? I seen plenty of cars that are fine on the driveway (even revving for 10 mins), but boil up when driving.
  2. Are you absolutely sure that repair on the radiator outlet to the expansion tank is ok ?
  3. Try doing a few miles with the pressure gauge connected, and then lift the bonnet after 3-4 miles to check the pressure.
  4. Try the UV dye check. Dye & Torch kits are cheap.
Even a small hard to find leak can allow the coolant to boil & release gas into the cooling system, hence hissing & pressure.
 
Only problem I had was a blocked (collapsed) breather pipe. The one that goes from the tank, out to the floor.

The pressure was so high it blew the tank cap off. :(
 
pwood999 said:
I agree that the pressures look ok, but . . . .
  1. How hot was the engine, and how long was it running ? I seen plenty of cars that are fine on the driveway (even revving for 10 mins), but boil up when driving.
  2. Are you absolutely sure that repair on the radiator outlet to the expansion tank is ok ?
  3. Try doing a few miles with the pressure gauge connected, and then lift the bonnet after 3-4 miles to check the pressure.
  4. Try the UV dye check. Dye & Torch kits are cheap.
Even a small hard to find leak can allow the coolant to boil & release gas into the cooling system, hence hissing & pressure.
Click to expand...

Your first question I had it running for about 20 minutes with revs on to simulate a normal journey.

I had a really good look for leaks that pipe I repaired was the first thing I checked

I can't close the bonnet with the pressure test kit attached. So driving would be difficult lol

Will keep poking away.
 
god forbid, but a leaking head gasket can push gases into system without oil/water mix..
there is definitely no sign of gas in the coolant?
 
Mark Piercy said:
god forbid, but a leaking head gasket can push gases into system without oil/water mix..
there is definitely no sign of gas in the coolant?
Click to expand...

I can't smell any gas in the coolant but then again I'm not sure what it would smell like, I just think it smells like warm antifreeze. Nasty

I am going to run the head gasket test again, but the engine runs sound, no signs of white smoke from the exhaust it's not lumpy apart from when it's first started after being stood for a couple of days.

Roll on the weekend I need Saturday for the daylight.
 
have you compression tested it.
lumpy on startup could be burning off water!
a slight difference in compression is alright but you can help to rule it out with further investigation..
not wanting to evil eye your fine machine buddy. Keep up the homework!;)
 
Mark Piercy said:
have you compression tested it.
lumpy on startup could be burning off water!
a slight difference in compression is alright but you can help to rule it out with further investigation..
not wanting to evil eye your fine machine buddy. Keep up the homework!;)
Click to expand...

Hi Mark.

I have a compression test gauge, I will add it to the list of tests.

Cheers

John
 
If the vaporisor is leaking you can get LPG in the coolant. If my new cap doesn't sort out mine i'm going to bypass the piping to the vap to rule out.
 
Just had a similar issue on the TVR, ran a sniff test on the coolant expansion tank, and the fluid turned yellow. Got it booked in for new (composite) head gaskets, head skim, new cam, followers, timing chain, etc.
 
As they said above....I am wondering if the Vap is leaking causing your pressure problem and also creating an airlock!
 
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