1.8 K-Series Headgasket Choice - Advice Please.

[Sonic ZS]

Firstly, let me start by thanking all of you who have replied to this thread, and sent me a PM (cheers Allen ), it would seem that yesterday I finally found the problem....and I'm sorry to say that it wasn't caused by either the thermostat, head gasket or radiator - all of which have now been replaced

On Friday, after I'd fitted the new radiator and also swapped over the underfloor pipe flow (to get hot entering at the top of the radiator - still not entirely sure if this is correct for a TF ?? But it works...), then removed all the pipes to clean internally and check them through for obstructions, I ran the car up again, only to find the exact same problem STILL existed - albeit slightly improved by the now unblocked rad.

However, letting the engine run on for a little longer than previous, I noticed the interior heater went cold after the first 'heat cycle' of the fan cutting in and the engine temp dropping slightly (varying from 105*C down to about 96*C) and the new rad was becoming cold too.

A friend (who was also scratching his head) commented that it was just as if the front half of the car's cooling circuit was being 'cut off' each time after the first warm up. Thinking over the weekend about this comment, I began checking up on boiling point verses pressure...

I was pretty certain the TF system should run at 15psi and Googling showed boiling point to be around 120*C at this pressure, but this TF was boiling at approx 106*C

Now...the hot pipe from the front of the head on an F/TF comes out then drops down vertically for about 12", to carry the coolant under the floor of the car to the front. Could it be that the boiling was causing steam within the head which then moved forward into the vertical pipe, creating an airlock effect which then prevented any further flow of coolant around the system...??? The idea certainly seemed to fit with all the results - as this would give an initially hot heater that would then cool once the boiling started. But why was it boiling so early, as the very first thing I'd tried was a new cap, so surely the system pressure must be correct ?

Not having a proper coolant pressure tester, I rigged up an old tyre Shrader valve into the system, blanked off a hose and pumped the whole thing up with an electric tyre inflator. It'd be impossible to over inflate the system, as the cap would release. But I could then take a pressure reading using a tyre pressure gauge...

Amazingly, the brand new cap (supplied by my local factors and made by 'First Line'), yes, you've guessed it, was releasing at around 7.0psi whilst an old cap which had been lying in my garage all along actually went up to 17.5psi, dropping back to around 14.5psi after about a minute.

So, old cap fitted, diagnostics connected to show engine temp, engine run up and hey presto...no more boiling, engine fan cutting in exactly as it should, temperature cycling up & down (106*C to 95*C) and the interior fan blowing hot constantly whenever the blower was switched on

So the moral of this story is: NEVER TRUST A NEW PART TO OPERATE CORRECTLY.

Only trouble now is that the increased pressure has highlighted a couple of holes in the original steel coolant rail, which is completely hidden on a VVC TF - oh, will it ever end....

[kaiser]

A hot heater is sign of water in the system. A cold heater is sign of no water, or stagnant water, in the system.
The car should not overheat, even if the cap vents early, provided it gets cooling air.
An air/steam lock would not stop water from circulating. Steam in a pipe does not stop water from flowing.
Steam or air around the water pump does!
Or a water pump problem does, or a lack of water.

While I hope the problem has been found, I fear it has not.

[Sonic ZS]

Don't worry Kaiser, I've carried out a temporary welded repair to the rusted coolant pipe and now tested the car for around 25 miles on one of the hottest days of the year.

This included both town and dual carriageway driving, the diagnostics showing 86'C whilst sitting at the legal maximum, rising to the low 90's whilst queueing in traffic. So whether my comments on the exact location of a steam pocket were correct or not, the fundamental problem has finally been found - low coolant pressure.

New stainless pipes are now on order, along with a low coolant level kit, just to ensure there is an early warning should a problem develop in the future (although this is probably unlikely, with everything I've now replaced...)

[kaiser]

Originally Posted by Sonic ZS

Don't worry Kaiser, I've carried out a temporary welded repair to the rusted coolant pipe and now tested the car for around 25 miles on one of the hottest days of the year.

This included both town and dual carriageway driving, the diagnostics showing 86'C whilst sitting at the legal maximum, rising to the low 90's whilst queueing in traffic. So whether my comments on the exact location of a steam pocket were correct or not, the fundamental problem has finally been found - low coolant pressure.

New stainless pipes are now on order, along with a low coolant level kit, just to ensure there is an early warning should a problem develop in the future (although this is probably unlikely, with everything I've now replaced...)

It is not the pressure that has solved your problem, it is the stopping of the leak!
Have a look here, almost carbon copy of your experience! https://www.the75andztclub.co.uk/for...=265008&page=3 see in particular post 21.
I today noticed I forgot to fit my cap to the expansion bottle on my F.
Been driving around for 3 days without it. No pressure, no overheating, little water loss, most likely evaporation! High pressure is only there as a function of temperature! in a normal system.

[Sonic ZS]

Sorry if I've confused you Kaiser (I know this thread has quite a few updates from myself as diagnosis & repairs took place), but the car did not originally have a coolant leak - this only occured the moment the cooling system was run back up at it's original design pressure - approx 15psi.

The original problem was that the engine was boiling, subsequently found to be at around 106*C. And as I'm sure you're aware, at 15psi water boils at approx 120*C.

You are quite correct that high pressure is a function of temperature, but the mechanical properties of a pumped cooling system are such that under normal circumstances the system must not boil to allow effective coolant flow to be maintained.

With a weak pressure cap, the boiling point will be greatly reduced and as such, the car was initially being tested whilst idling in a relatively high ambient temperature, so no natural airflow through the rad or engine bay - possibly the worst possible scenario for testing the effectiveness of the cooling system.

As you will have read, various items were replaced in an effort to find the fault (the cap was actually the first item to be renewed, but the new replacement was subsequently found to be faulty) and when the system pressure was eventually tested, a good cap was fitted and the problem was instantly solved.

Unfortunately, the steel coolant pipes had been seriously weakened by rust over 16 years and the sudden return to 15psi then showed up the weak spots !

[kaiser]

I don't want to be pedantic here, but a lack of water is the only explanation for what you have experienced.
You are confusing cause and effect. You have lost water, which has caused air around the water pump, and a lack of flow in your system and overheating.

You are correct with regards to temp and boil etc, but your engine will never get to 106 degrees if your cooling system works! that is full, and fan running.!

You have stopped a leak, and that has cured your problem.

But what you choose to believe is obviously your choice!
I am not looking for an argument

[Sonic ZS]

No need to worry about being pedantic Kaiser, I think you are just missing some of the information that I've noted earlier in the thread...

For example, you say that 'You've lost water' - this is NOT correct. As you will see from my earlier posts, the problem has always been that the engine boiled up after the first 'heat cycle' from cold. There is absolutely NO MENTION of the problem being that it's losing water.

Secondly, you state that in losing the aforementioned (...which the car wasn't ) I've managed to get air around the water pump ? Please could you explain how air could get sucked into a pressurised system, one that was actually running at 7psi, fully bled and with ample fluid in the header tank ??? It's simply not possible, physics does not allow it. Hence, as previously mentioned by myself, it would have been steam that caused the coolant flow to stop, either in the water pump (as you stated), or as a lock within the vertical pipe at the front of the engine - neither one of us will ever know for certain (unless we fit transparent parts to the engine and view what goes on inside... ). Any leak in any pressurised system would have caused the water to escape - not air to get sucked in (that'd require a vacuum ).

Thirdly, you say that my cooling system will never get to 106*C if it works properly - well that's kinda the whole reason behind this thread, and the car has not only been connected up to a professional 'Snap-On' diagnostic computer which clearly states 'Coolant temperature', but readings were also taken with a laser thermometer and a sensor connected up to a multi-meter - so highly unlikely that all three items could be wrong

Lastly, the temperature at which the radiator fan switches on, on this TF, is 105*C. However, this is read from the sensor located at the front of the cylinder head, towards the back of the car. As the car is mid-engined, it takes far longer for the return water from the front rad to get back through the underfloor pipework, thermostat, pump, through the block and eventually onto the sensor to cool it. So with the engine continuing to run, it is perfectly feasible for the temp reading to creep up to 106-107*C (and the boiling to start, due to lack of correct pressurisation), before the now fan cooled water finally reaches the sensor and starts to bring the reading down. Trust me on this, I've been watching it happen on many occasions over the last couple of weeks.

So to say it will NEVER reach 106*C (on a car you've never seen, or been 'hands on' with) is quite simply incorrect.

I do appreciate your's and everyone's help with this, but I find it interesting as to why you seem to want to disagree with not only the initially stated problem, but with my subsequent findings and diagnosis ??

But then, I'm not looking for an argument either...

[Ratty]

Glad you have it fixed now Paul, happy driving.