Dead Cert Way for Diagnosing Head Gasket Failure

[tobytronicstereophonic]

Replenish the lost coolant, properly bleed the system and run engine up to temperature and wait until it has completely cooled down.
Then slowly unscrew the pressure cap.
Any residual pressure, whatsoever, is a leaking head gasket. Unless the gasket is so far gone - which should be obvious - and assuming the pressure cap is good as well as no other coolant leaks to bleed pressure, then this is a very reliable test.
It has served me well for the last 30 years and literally 100s of vehicles, particularly modern ones, at the very early stages of gasket failure.

It is also a useful check to confirm a new replacement head gasket job is a success.

On Liquid Head Gasket Sealants:
When times were financially bad for us, I remember foolishly buying a £150 Citroen XM 2.0 with a blown head gasket. It was leaking bad enough to throw all of the coolant out within two miles or so. Too skint to do a decent repair, I bought a bottle of K-Seal.
My wife had a work meeting in Birmingham the next day, a 260 mile roundtrip. Yep.
I fully expected to breakdown, especially when stuck in a long M6 traffic jam, but it worked for the next 6,000 miles. This was a cast iron block. I've tried it on numerous alloy block, wet-liner engines with zero success. Not even as a limp home option. Useless.

Finally, the only other 'liquid spanner' product that unequivocally worked for me in the last 45 yrs of occasionally wasting money on them, was on a Citroen GSA. It's an aircooled flat-four car and was absolutely pouring engine oil from the rear crankshaft oil seal. Bad enough that you could follow the black trail miles back to the Village Church where he was Vicar.
I was foreman at a main dealer where he got the diagnosis. Quoted £1100 plus parts - clutch set and seal £169 - so I suggested he try 'STP Stop Leak' because he couldn't justify this expense on a car that now had no cash value...

And my God did that stuff work. I pressure washed the oily gunk away inside the bell-housing and it was still doin' its thing 20,000 miles later. Amazing.

So, I am typing this tosh for self-justification.
Four weeks' ago, I pressed/pulled the trigger and came out of retirement. I rented a workshop. A big one. My plan is to resume where I left off in 2001.
Which is ages ago.
Fixing Citroens again. Old ones. Datsuns too, as that's what I served my time on.

In my sixties with multiple health 'things' and the body of an eighty-three year old stallion.

The only two worthwhile bits of advice I ever heard are these:
Do not use your teeth as tools. Never lie down on a cold concrete floor. Oh, a third one: Don't Drink Petrol.

Wish me luck, please :-)

[DKS]

Good luck!

Although I would normally agree 100% with you on HGs, one of my cars seemed to lose coolant and retain pressure in the system. I was monitoring and preparing to change the HG but one day topping the coolant up I dropped the cap behind the battery which is inaccessible without removing it, so I borrowed a cap from another car and it completely cured the symptoms. This was about in the middle of the 60k I've covered in this car so far.

Also, a bit of gunk on the oil cap does not mean HG failure unless the coolant is dropping. As soon as a picture of a oil cap with even the smallest bit of mayo appears on FB they'll have 200 replies saying HG, with half the people saying swap the engine!

[Krikkit]

Depends what kind of HGF you have as to whether the radiator test will work.

[TwinKam]

Good luck Toby! ...stick to the old stuff for the sake of your mental health alone, a lot has changed since 2001.

[Maxdecel]

tobytronicstereophonic said:

The only two worthwhile bits of advice I ever heard are these:
Do not use your teeth as tools. Never lie down on a cold concrete floor. Oh, a third one: Don't Drink Petrol.

Wish me luck, please -)

Or the contents of the battery, I'm told handbooks have this useful piece of info.
All the very best, I escaped a good few years before you; returning I could never contemplate.

[vikingaero]

You can get this sex toy looking head gasket tester from Amazon:
https://www.amazon.co.uk/Block-Tester-Bt-500-Combu...

You insert it into the coolant tanks, pump and the chemical changes colour. Popular with some American YouTubers.

[Old Merc]

vikingaero said:

You can get this sex toy looking head gasket tester from Amazon:
https://www.amazon.co.uk/Block-Tester-Bt-500-Combu...

You insert it into the coolant tanks, pump and the chemical changes colour. Popular with some American YouTubers.

I used that professionally for years, it works, takes a minute, costs nothing.
All you do is remove the radiator cap, and let it “sniff” the vapour. If there is exhaust gasses in the coolant the liquid will change colour.

[bearman68]

tobytronicstereophonic said:

Four weeks' ago, I pressed/pulled the trigger and came out of retirement. I rented a workshop. A big one. My plan is to resume where I left off in 2001.
Which is ages ago.
Fixing Citroens again. Old ones. Datsuns too, as that's what I served my time on.

In my sixties with multiple health 'things' and the body of an eighty-three year old stallion.

The only two worthwhile bits of advice I ever heard are these:
Do not use your teeth as tools. Never lie down on a cold concrete floor. Oh, a third one: Don't Drink Petrol.

Wish me luck, please :-)

It's not a bad time to do it. Mechanics are a dying breed, especially those that will work on engines, and I see garages shutting up shop for lack of fitters, and rising electric prices. I reckon before long you will be rushed off your feet, and wondering what the hell you've got into. Best of luck OP, I will keen tuned for future updates.