KV6 190 persistent overheating

[Ducati750cc]

As T-Cut says such a rapid increase in pressure suggests head/gasket/block problems, time for a leak-down, compression, and sniffer test before you start dismantling anything, using these will help to point you in the right direction.


The previous, several, overheating episodes won't have helped.

[xsport]

i wonder if the k. seal boys have been at work. ... would not be the first time similar problems have appeared on here with relatively newish members. maybe the o.p could advise how long he has had the car. ...

[mgb66]

Thanks everyone as always for your thoughts on this.
Simon kindly came over today and helped with some more investigation.
dave lincs suggestion of bypassing the oil cooler proved an interesting idea and a slightly mystifying result that is difficult to explain.

With the cooler not in the circuit, the previous and recurring issue of the rapidly rising level to overflowing of coolant in the expansion tank did not happen and once up to temperature the pressure cap was put back on.

However the engine temperature continued to rise until the fan cut in c. 101. The fan did not check the temperature and when it went up a couple more degrees the engine was turned off.

We then checked the flow through the oil cooler using a garden hose and this seemed not to be suffering with any kind of blockage.
The oil cooler hoses were reconnected and the coolant level was returned to MIN as before after checking there was a steady flow from the bleed screw.
The engine was re-started and again there was no rapid rise of coolant in the expansion tank.
The temperature followed the same pattern as previously rising quickly until the fan cut in.
The top hose to the radiator was not appreciably hot to the touch on either occasion even when the engine temperature indicated 103, but the oil cooler hoses were. Given that on a 2004 ZT-T these hoses appear to be in circuit with the heater which is fed by the bypass in the thermostat housing this makes some sense.

Given any justifiable concerns about possible HGF all this would seem to indicate thermostat failure as well since there seems not to be any flow in the main engine cooling circuit.
On discussion it was decided to investigate the operation of the thermostat further before embarking on any heavy re-engineering of this KV6!
We also did briefly touch on the demise of the internal combustion engine in conversation but let's not go there! It would be good to get a few more years out of this one...

Peter

[mgb66]

Apologies xsport, I bought the car in August 2018. No hint of K-seal in the invoice history but there was a two year gap in the service record when according to the seller it was 'looked after by a mechanic friend'.

In the first week of my ownership the clutch disintegrated and after driving off from the repairers full of relief, within a few miles, the engine suffered the first of its overheats.
I was furious with the repairers but they swore they had not touched the cooling system, and here we are still on that particular journey.

That Christmas a Post Office van ran into the car while it was parked outside the house which I saw as I happened to be standing at the window. The car was deemed beyond economical repair and written off. Having already invested in the car and already rather fond of one of the final MG Rovers which is the reason I bought it, I accepted the settlement payment and spent it on putting the damage right.

I'm sure we've all got our tales to tell!

[SD1too]

Originally Posted by dave lincs

Hi Peter
Try bypassing the oil cooler this will stop the coolant flow if blocked

Dave

As Peter has reported I went over yesterday afternoon to see if I could help. His engine has the later oil cooler in the heater return circuit. Nevertheless this was checked and found to be flowing freely.

Since there is now no ejection of coolant at temperatures up to 103˚, the prospect of head gasket failure is receding. In the coming days we will be removing the thermostat to check its operation since the indications at the moment are that it's not opening properly. The bottom radiator hose is stone cold.

Simon

[mgb66]

After receiving some most valuable practical help from Simon (SD1too) last week, and sound advice from Dave (lincs) I decided to attempt to change the thermostat by the keyhole method.

The concern about possible HGF seemed to be lessening as there were no obvious further indications of that dreaded scenario, but the car either had to put back on the road or more difficult decisions might have to be made.
I was struggling to get hold of the parts at short notice but having ordered just a thermostat from Euro Car Parts that would be available on Saturday, MG Rover Parts of Sandy were extremely helpful and took a thermostat kit to the local Post Office on Friday afternoon, and via Special Delivery the parcel arrived at eight o'clock the next day.
No excuse for not getting the job done on Saturday then!

I took out the air filter and throttle body as recommended and removed the various breather pipes, plus I undid the bracket that provides some fixing points to make room to get my hand in.

I part drained the cooling system via the bottom radiator hose, and having removed the hoses from the thermostat and curved pipe I undid the 8mm bolt and proceeded to try and remove them. This proved to be a matter of a lot of jiggling which loosened both items but not fully. As the order is curved pipe out first I found that an old spark plug box spanner fitted inside the opening of the pipe quite snugly and allowed some futher enthusiastic movement back and forth without too much fear of breaking it.
At last the pipe came out, and the thermostat followed without a fuss bringing the straight pipe with it.
I noticed that there wisps of a black material around the O rings and on closer inspection this seemed to be the remnants of some kind of sealant.
This sealant was in fact all over the cylinder block ports and it took some time to clean them using a silicon remover and then some wet and dry.
After being forced into the house a couple of times by the heavy rain, now was the moment of truth as I started to fit the the new thermostat and associated pipework.
With the aid of some Fairy Liquid wiped over the O rings, both the thermostat, with the straight pie already connected, and then the curved pipe went in without much fuss. The hard part proved to be squeezing the clips together on the straight section. Eventually I managed to get a pair of plumbers grips to bring the ends of the clips together and they are now tight and in position.
As the bleed screw was now much easier to access without the throttle body in position, the expansion tank was raised up and the cooling system re-filled.

I then reversed the rest of the dismantling procedure, and had a cup of tea prior to starting the engine.

Having selected the diagnostics temperature reading I kept the car at 1500 hundred revs, and the temperature rose gradually taking some eight or nine minutes to reach 95.
When 100C was indicated the fan cut in and the temperature began to drop to 96.
I took all this as a good omen and decided to put the undertray back and take the car for a short drive.
Replacing the undertray took some time and effort, and as the engine had now cooled, I checked the coolant level which needed a little topping up.
The short drive, about ten miles, produced an average reading of 95C apart from a bit of rapid accelaration up a slight gradient. This got the temperature up to 100 which soon came down.
I've since made a few short journeys checking the coolant level in between. Only a small amount of topping up was needed and nothing after the third outing.
Thoughts of HGF failure or other damage from the overheating are receding, though time will tell if there will be further consequences.

Personally I would definitely recommend the keyhole method for renewing a thermostat on the KV6. Why disturb gaskets and O rings etc., all of which could be added headaches?

The job did take me a good few hours but that was with breaks for downpours and showers.
Thanks again to everyone for all the help and suggestions. It's a great relief to get the car back on the road and here's hoping the engine does not need any more attention stemming from the overheating.

[dave lincs]

Well done Peter glad all is now sorted I told you it was quite an easy job