Rover 75 2.5 KV6 - Puzzling Cooling Issue

[SD1too]

Originally Posted by xsport

Some members disagree , but i think they have the black expansion tank which may or may not do this.

I have a black expansion tank Stefan and I can confirm that it has the air bleed hose which you've described. If the cooling system has been effectively purged of air, a constant stream of coolant should been seen to enter the expansion tank from this hose when the cap is removed.

The only difference between the black and the beige tanks is that the black has a short overflow tube pointing downwards but the beige tank vents coolant directly from the cap.

Simon

[xsport]

Can i ask you simon if the caps are identical in design and release pressure on both the black and opaque types are the same.The cap itself could be faulty,but the excessive build up of pressure is not correct. I also wonder if there has been an overheat at some point here before the change of thermostat, or just a coincidence. One thing is for sure, and that is that the thermostat is not working correctly , not bringing the block up to temperature. Has it been gutted to keep the temperature down if the fans are not working ?Or a genuine faulty one. Demist test should tell you if fans are ok. Any traces of contamination in the sump oil ? i also wonder if there may be a problem with excessive crankcase pressure past liners ..... the list goes on. The sump oil level needs a good inspection to rule out some possibilities and contamination. Next job on my list would be to change the thermostat first, and then take stock again . Thermostats can stick open and closed or close off and open again in an erratic manner at any temp.sometimes the springs jam . Hope this turns out to be an easy fix , but the longer it goes on, the less the probability....

[SD1too]

Originally Posted by xsport

Can i ask you simon if the caps are identical in design and release pressure on both the black and opaque types ...

My cap is the original "100" type (but with new 'O' ring seals). According to RAVE these were standard on the petrol engines but the higher pressure "140" is specified for the diesel. I understand that this later became the standard, probably for economic reasons.

Matt's reported steam from the exhaust and explosive depressurisation after a long cooling down period so I can understand his suspicion that exhaust gases are entering the cooling system. This car is a recent purchase so we cannot be certain that a head gasket hasn't been damaged under previous ownership.

In addition, the long warm-up period and low displayed running temperature suggests a thermostat failing to close. This may be a rare failure or the result of K-Seal (or similar) contamination. Matt's also photographed jelly in the expansion tank and I wonder whether that's engine oil emulsification as you've mentioned Stefan.

Originally Posted by Matt_75

Can anyone help with any suggestions on what to test next?

The bottom radiator hose, that is the one containing the bleed screw, should remain cold until the thermostat opens. If it warms up regardless, that will justify thermostat removal for inspection and replacement. If we can get the engine to run at the proper temperature it will be something!

The pressurisation is a worry though. We're in the territory of a set of symptoms which don't fully make sense and that makes me suspicious that K-Seal has been used.

Simon

[xsport]

Thankyou simon .That the engine is not running up to temperature , may be hiding any issues . If the stat is replaced and we can get this block temp up to 100 + degrees , before fans come on , then any head/ cracked liners etc maybe will come to light. The test may then show positive for exhaust gases at this pressure and temp. I hope not but its a possibility that if there is a breach somewhere , it will then be exposed. Thing is ,the thermostat needs replacing anyway, as the existing one is not working. It may be getting by now in this weather , but there will come a time in hotter weather , in non moving traffic ,with no ram effect that the car may overheat. Hence my question .. are the fans kicking in ....

[Matt_75]

Thanks for your help Simon & Stefan.

I appear to have a good flow of coolant from the air bleed hose when the cap is removed. I have a spare black expansion tank (taken off a well running car) that I'm going to swap and a brand new cap on the way, just to fully eliminate these.

Last time I checked, admittedly a few months ago, the cooling fan passed the demist test. The previous owner has also fitted a replacement resistor. I will double check it's operation and report back though.

I'll check the bottom radiator hose as described, Simon. I'm also going to try to check that the radiator is evenly hot and check that both sides of the interior are getting equal heat from the matrix.

For context, the previous owner was a member on here and had some issues with coolant loss that you may remember (it was 6+ years ago though): https://www.the75andztclub.co.uk/for...d.php?t=273030

I need to go through his previous posts and the paperwork that came with the car and try to make sense of it all. When we took on the car, he said that it ran well for a good while after having the front head skimmed and a new head gasket. He said it then started ejecting coolant on long journeys but never overheated.

I'll do some reading and tests, then report back. Thanks again!

[xsport]

Mat can you check the oil for contamination and let us know if it is . Simon is very correct to suggest that it may have had some type of sealant added at some point.If the expansion tank shows this then the heater matrix has the same issue, even if not fully blocked. Known or unbeknown to you , this was probably the last throw of the dice , in an attempt to cure the coolant loss. I would never never ever use this stuff.It never sorts the problem correctly and only papers over the underlying issues. For an engine that has had severe overheating ,burning out valves , and probably warping the head , and blowing head gaskets , It makes me wonder how much was taken off the head and if the damage was rectified correctly, if at all . You say the car is very quick ,compared to your other KV6 , well a large increase in compression may account for this, and would not run lumpily ,as the banks fire alternately. You will have to, at some point attempt repair of the thermostat,which could well be gummed up as well. Whatever you decide to do, dont scrap the car. There is a member on here currently asking what to do with his mothers unwanted KV6 and there could be a solution for both of you here, even you only want the heads from his vehicle. ...... have a think ....

[SD1too]

Thanks very much Matt for the extra information and particularly for the link to the previous owner's thread. In that, he claimed success by following my suggestion of a full drain, refill and bleed but that was six years ago. It appears from your posts that the problem recurred. Has he revealed to you whether his response to that was a sealing product after all?

But a potentially more likely reason has now surfaced ...

Originally Posted by Matt_75

When we took on the car, he said that it ran well ... after having the front head skimmed ... He said it then started ejecting coolant on long journeys ...

Hmmm. All the evidence (coolant loss, steam from the exhaust, low running temperature, residual pressure, jelly in the expansion tank) could be the result of an imperfect seal between skimmed head and gasket.
I know it's a daunting prospect but replacing that skimmed head with a brand new one might be the answer. Rimmer's have them but pour yourself a single malt before looking at the price.

What do you think Stefan and Matt?

Simon

[xsport]

Make it a double simon .... It all boils down to the individual. Mat may or may not either wish to, or can do the work himself, or want to pay someone else to do it. The thing is that you will not get a definitive diagnosis without a strip down. Lets be clear here . It is possible that a cylinder liner could be cracked or other issues could be present , and it would be unfair to try to diagnose without a strip down. I would be leaning towards making an approach towards the KV6 connie thats up for grabs .Lump out or heads .. its a win win . Lots of spare parts and extras as its a connie , and with two R75 already in the family to keep going ... If no one wants it , it goes to the bone yard at the end of this month according to the O.P .Alternatively both of these cars will go to the scrapman for £250 each ...... eventually. ... very sad...

[Matt_75]

At £1,800+ per head, it won't be getting new ones! The car won't be scrapped either though. It's my wife's modern classic (she has a Fiat 500 for daily duties) and she's very attached to it. I'd go down the 2nd hand engine route if it comes to that. However, I have some updates that I think are significant.

We idled the car for a good length of time today, about half an hour. It would not come up to temperature fully according the cluster read out. Highest we got to was 88 degrees.

We compared the amount of 'steam' coming out the exhaust to both my wife's 500 (which has a 1.2 litre petrol engine) and my KV6 75. All three were comparable, the typical amount you'd expect to see on a fairly cold winters morning. As the engine got to near operating temp, the exhaust cleared.

The top of radiator was hot to the touch at 88 degrees.

Importantly, we ran the heater inside the car. The drivers footwell got lovely warm air, however the passengers side did not. It stayed cold throughout. I think the next course of action is to investigate the heater matrix.

Thoughts?

Edit: I forgot to mention that after running the engine yesterday for a few minutes, I opened the cap to let the pressure out. I didn't run it after this. A few hours later I came back and opened the cap again and it let out a hiss, suggesting it managed to build some pressure. Perhaps from the residual heat in the engine? I wasn't sure whether this was significant or not.

Thanks for your continued help chaps, it's very much appreciated.

[SD1too]

Originally Posted by Matt_75

Thoughts?

• I'd expect you to need only one cylinder head to replace the skimmed one.
• Don't change the whole engine! You risk picking up a heap of new problems. A second-hand head is a better option.

Originally Posted by Matt_75

We idled the car for ... about half an hour ...Highest we got to was 88 degrees.

Idling isn't a good test. The engine needs to be put under load by driving it in order to generate normal heat.

Originally Posted by Matt_75

The top of radiator was hot to the touch at 88 degrees.

It's the bottom radiator hose that is significant Matt, as mentioned in my post no. 13. It should stay cold until the temperature display reaches the thermostat opening temperature of 88˚. Can you report back on that please?

Originally Posted by Matt_75

I think the next course of action is to investigate the heater matrix.

That's the least important thing Matt! It won't affect the low running temperature or produce coolant loss or excessive pressure.

I think you need to give serious consideration to the likelihood that the LH cylinder head skimming and gasket replacement is responsible. This is major work which may not have been carried out to the highest standards. If there's a defective seal here it can:

1. Prevent normal pressurisation of the cooling system which produces low and variable coolant temperature instead of it being stable.
2. Cause exhaust gases to enter the cooling system producing the smell you reported and the high pressure hours after the engine was stopped.
3. Emulsified oil in the expansion tank as seen in your photographs.

Simon