XJ6 series 3 headgasket failure

Hi all, I recently had the head gasket blow from number 6 cylinder into the timing cover
pretty well one third of the gasket it was caused by a Hydrolic lock due to a failed new fuel pressure regulator, the car was facing down hill on a steep drive and I removed over 1.5 litres of fuel from the manifold. The reason I am asking I have a claim against the supplier and they are blaming the gasket my aim is to prove its not a normal failure, as they are claiming what happened to me has not been seen before.

You’re saying you were parked downhill and the #6 got flooded with fuel (I had that happen) and hydrolocked, this blew the very small amount of head gasket towards the timing cover?
It might be a normal failure, but I bet it would have lasted much longer without the fluid hammer.
All that makes sense to me. What I can’t understand is how any failure of the pressure regulator can flood the engine. The pump shouldn’t run when the engine is not running and the engine likely won’t run well with pressure too high… now, to flood the cylinder(!), something must have gone terribly wrong, what is your theory?

In order to succeed in the theory that the fuel pressure regulator was responsible, you must prove it. A test by an independent expert to show that it “allowed the fill l 100 PSI” of the pump to fill number 6???
How does the number 6 injector fit in to that that theory?

Likewise, the vendor’s theory as to head gasket failure has flaws.

Agree as to something badly astray as to so much fule finding it’s way only in to number 6???


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#6, parked downhill, would allow it to fill first…but I still want to see injector failure or the diaphragm torn (thus filling the plenum via the vacuum hose).
Sounds as if they swallowed the component failure and the resulting flood - but not the resulting head gasket failure?

But, is it excess PSI? Only the fuel pump cold do that if running. Gravity ? Enough PSI to bust a head gasket?


I assume the fuel somehow collected in the plenum and eventually flooded the cylinder. Then, he cranked.
We need more information.
Especially on the fuel pump. How did it all fail?

Ok long story, replaced the original to rectify random hot start issue cured it straight away, went to move the car from the garage a week later started fine but running rough as if it had too much choke wanted to warm it up as I didnt intend to drive anywhere so kept it running with my foot, it cut out! Found coolant on the dist cap from a small leak thought that was it cleaned it off tried again same thought maybe cap had a carbon track caused by the coolant bought a new one fitted it went to start it baulked on the starter fired and made a lound mechanical noise. I could smell a lot of fuel and found a large amount of fuel in the manifold removed that took off the vacume hose from the new regulator and cranked the car a lrge amount of fuel shot out of the regulator onto the passenger inner guard. Rang suppliers and went and exchanged regulator took it home fitted it and when I started it it was missng and while trying to isolate the cylinder it started to smoke heavily and was pushing oil passed the rocker cover gasket, i turned it off and found no compression on number 6 and the plug completely oiled. So in summary its a unique combination of things and probably would not have happened if the driveway wasnt steep and the car facing down hill, so as I was cranking trying to start the car fuel was entering the manifold unrestricted unitl it filled the front of the manifold & number 6 cylinder, the claim is thet it was not the failure of the FPR that caused it, that the gasket just failed is one hell of a coincidence,. It is now a matter of principal to see it through I can fix it myself no problems as I am a mechanic by trade. I am asking if anyone has had a gasket fail in this way before so extreamly as I dont see this as a normal failure of the gasket as it has done therefore giving more weight to my argument I am not a litigious person only want whats fair just want my car fixed to how it was before this happened

Hi David should see the amount of fuel that comes out of the regulator when its unrestricted and it will run as long as its being cranked

Oh I should ad this is a claim against thier liability insurance I bear no animosity towards the supplier or those working on the car their theory falls down as soon as all the facts are viewed as a whole by ignoring any of the critical points, the claim that the manifold cant fill with fuel but it doesnt need to fill the down hill facing of the car means only needs a smaller amount, so they also state that the headgasket wasnt seated correctly at the bore, I say it was running perfectly before it happened and most lkely would have done so for many years and as its a toy, even it only lasted 50k thats around 10 years of motoring as I am using it now.

I see that but I thought it still had to go through the injectors!
Now thanks to your long story it is obvious that it happened because of the regulator, and that it is absolutely not your (or the gaskets‘) fault.
Now your failure is the worst I have ever seen. That is definitely caused by the fuel, I‘d even be worried about the conrod.
I wish you good luck, you deserve to get this fixed. I could see this happening to anyone with a regulator that leaks through the vacuum port into the manifold. Also it is unlikely that anyone would have recognized the issue before it hydrolocked. It shouldn’t matter whether it happened because you were parked downhill or not, and that the headgasket can be seated wrong is absolutely new to me. If that was the case it‘d have leaked for ten years with obvious consequences.
You’re in the trade, and have all the arguments in your favor.

If the gasket had sprung a leak, well maybe one hell of a coincidence, but that exploded.
I hope you don’t snap any head studs putting it back together.

I actually dropped it off at thier workshop with the potential of being charged for the work but am so confident that cause and effect was the regulator, so now the workshop has the car head off and apprently the chain guide is worn out, more complications.

Litigious or not , Simon - it just would be nice to know what happened…

On viable option, blaming the pressure regulator is a failed membrane in the pressure regulator. Fuel, under fuel rail pressure, will then be forced directly into the manifold. The rail the pressure is mainly controlled mechanically by spring load to some 36 psi (which is fairly reliable) - but if the return lines are blocked; rail pressure will reach pump pressure.

Such regulators failures are fairly easy to verify - and you may have case.

Parked nose down the liquid fuel will drift towards #6, but can only enter the cylinder with the inlet valve open. Also, with the car parked; only residual rail fuel is available.

Whether that is enough to give compression pressure to cause the gasket to blow as described, is arguable. It requires a combination of factors (#6 open and enough fuel in the rail to drain into the manifold). And parked for a while; fuel would inevitably drain past the piston seals into the sump - and/or evaporate…

Certainly, such a regulator fault may flood the engine, preventing starting. However, cranking would also cause fuel vapour or liquid to be ejected on the exhaust stroke - preventing a proper hydraulic lock or indeed excessive cylinder pressure. The same applies to leaking/failed open injectors, which is irrelevant for a pressure regulator failure in blowing gaskets…

That a regulator is defective is easily proven - that it caused a blown gasket is not…

xj6 85 Sov Europe (UK/NZ)

This is not true, Frank.
My understanding is he cranked while the plenum filled up (the vacuum sucking the fuel from the regulator as much as the pump pushing in fuel), and I assume it wouldn’t take all that long. Soon enough, a small amount of fuel made it into the cylinder, enough to make it blast out the gasket on the compression stroke the first time it ‚hit‘. No higher understanding required?

@Cadjag will surely like the details on this.

I removed over 1.5 litres of fuel from the manifold after this happend

Aye it clarifies a lot!

Got the sequence of events fairly well understood.

The hydraulic lock busted the head gasket. Number six was the one because of gravity.

But, Simon, were this my case, in my former profession, I’d charge you with some contributory. “negligence”. Continuing to drive and crank an engione in distress . .

My career in insurance claims spanned fifty years. Cases such as this came in garage liability. I liked those from early on.

Aye, as David says, the lower end can’t fared well in the diluted lube!!

Somewhat on point are two events, one distant in time and the other more recent.

  1. School chum Roy, built a very nice A Ford. One mod was a down draft carb in lieu of the up draft. Merely flipping the intake allowed that!!! One day parked at school, down hill, the TWC campus is quite hilly. The needle stuck and flooded the crankcase. Would not start? No wonder no gas in the tank, all went to the crankcase!!!

  2. More recently, a You Tube case. J. C. Smith master truck mechanic and truck “flipper”. A big diesel lost a cylinder and would not run. Injector failure all the fuel went to the stuck unit and thence to the crank case…
    Could have limited the damage had the driver not continued to drive the engine with a clear miss.

Good luck with the claim, Simon.

Carl. .

I doubt negligence applies here, if I‘d done that I wouldn’t have seen myself as negligent either. As soon as symptoms showed (the hydrolock) the damage was done.
We all know they can take some time to start sometimes :slightly_smiling_face:
Diluted lube, I‘d not worry. But it must have been quite a shock and as far as I know the conrods might bend eventually. The XK is strong, though.

As the pump stops, the pressure regulator closes, David - and the construction of the regulator becomes interesting in this context…

Does a membrane leak prevent the fuel pressure from opening the regulator against the spring, maintaining the rail fuel pressure? Ie, will the regulator membrane leak with the regulator closed - or only when the regulator is opened by fuel pressure…?

Having experience a membrane leak; the engine ran normally, except for running a bit fat due to vacuum sucking fuel into the manifold. So I assumed the membrane only leaked with the regulator opened by pressure. However, that is guesswork…:slight_smile:

Parking downhill; with a leak through the (closed) regulator, gravity from the tanks, adequately filled, will certainly run through the regulator vacuum hose into the manifold - draining into open valve cylinders, draining further into the sump. Whether enough residual fuel remains to cause a hydraulic lock is conceivable, but such excessive fuel in the manifold would certainly cause a non-start. And continuous cranking will add fuel to the non-fire…:slight_smile:

The manual does not mention a leaking membrane in the regulator checks - only replacing the regulator if the rail pressure is out of spec. Which may or may not imply that a leaking membrane will give incorrect readings - even as the test is carried out with no manifold vacuum…

It’s an interesting theory, but also; with a leaking membrane under pump pressure only, may still deliver fuel to the manifold via the hose while cranking - even with the return likes open. But also; continuous cranking without start will also fill up the manifold through ordinary channels - enhanced of course by a leaking membrane…If we consider driver’s ‘contributory negligence’ as Carl rightfully mentions; I would also say that replacing the regulator, as Simon did due to a random hot start issue, without actually verifying original regulator function is not best practice.

It’s an interesting insurance case - in addition to the purely technical issue…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

We don’t know what made regulator fail, Frank… all we know is that there was a lot of flow into the plenum.
All that matters is that this high flow eventually made its way into #6 and blew the gasket: A small amount is all that is required to generate extremely high pressures, and my own experience was that the rings can hold the fuel for a surprisingly long time, and the force generated very high - the starter had no chance and I was lucky that the locking cylinder was almost at TDC.
And we know that it might have been a manufacturing error (no testing?), or due to age or storage. Thing is, the regulator failed and finding out about that in time is improbable. Negligence?
If you were changing the regulator you might expect some time to fill the fuel lines, and then some more as you never know whether the pressure from the old unit was different, the mixture adjusted, etc.- and you don’t know for certain how much consideration went into the replacement.
I maintain that the bottom line is that the failure of the regulator clearly (and unavoidably so) caused the gasket failure.

It’s not that I disagree, David - but the ones paying may…:slight_smile:

Some negligence can be attributed to the owner for fitting untested parts - though to test one should know how things work.

However, the regulator membrane may fail at any time, as happens occasionally - but then usually with little consequence. Fuel then just leaks out of the vacuum house connection. All of which is part of my interest…

Under what circumstance did the fluid lock happen to you - just to help avoiding such calamities…?

xj6 85 Sov Europe (UK/NZ)

You might remember, Frank - two years ago. You helped me with the problem, it’s in the archives yet I never found out - I suspect three injectors we’re open for a longer time. Something must have gotten grounded.
For future readers:

Not much of interest here