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Old 12th February 2024, 20:58   #51
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Glad to see that you are making some in roads mat . I dont think the car is bled properly and with airlocks still , more than likely. You need to get this car on level ground to follow the bleed /refill instructions exactly. Did you follow the instructions correctly ,via mgrovers recommended proceedure ? You dont mention holding the engine revs as suggested. The other thing that springs to mind is that the new thermostat has the new "lower opening temp " complained about by others. I understand that you need to move the car for access for the other vehicles , but the first job , and by far the quickest job, would have been the compression test. If this fails the test , all of your work with the stat is for nothing , and has to be repeated. I know that the last thing you want is to find that the heads are compromised, as i would too , but i still have a feeling that the "hiss" on the rad cap is trying to tell you something. The car can take quite a few runs to bleed itself through ,so keep an eye on the level in the tank. Does the rad/bleed tube run freely ,whilst warming up to temperature ,inside the tank, whilst observing its flow without stops and bubbles ,with the cap removed ? Keep up the good work Mat, and good luck. !!
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Old 12th February 2024, 21:07   #52
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It wont hurt to start her up and just leave her ticking over for an hour or more.This will bring the engine up to the fan on temperatures and down again, whilst opening the stat and releasing airlocks at temperatures that you are not experiencing whilst driving. This is the point of the fast 2500/300 speed recommended in the mgrover bleeding process ,to clear airlocks ,which usually surround the thermostat area.

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Old 12th February 2024, 21:15   #53
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Thanks for your help. I prioritised the clearing the cooling system as I was keen to get all traces of Steel Seal out of the system, but you're quite right, a compression test on it's own isn't a labour intensive exercise. I would like to combine it with setting each piston at BDC, pressurising the cooling system and using my boroscope to check the cylinders coolant ingress though, which obviously requires a bit more time and effort. I may also invest in a cylinder leakage tester, depending on the outcome of all this.

When bleeding the system the first time, I followed the MG Rover procedure very carefully (except for the error with the bleed hose). I kept the engine speed between 1500 and 2500 rpm until the cooling fan kicked in, then I let it idle until the fan turned off before then turning the engine off.

The second time, I again followed the same procedure (1500-2500 rpm) except for when it got stuck at 78°C and I let it idle for a bit to see what would happen. After lowering the front of the car back down, I continued with the 1500-2500rpm engine speed and followed the same steps with the cooling fan.

I'll see how I get on after this 2nd Bleeding attempt but think I may need to do a drain and refill on level ground (my driveway is sloped unfortunately). I'm tempted to attempt vacuum filling it as I have all the kit to do this, but have never attempted it before. It would be interesting to see if the system is capable of holding a vacuum?

I do wonder whether this is all being driven by a head gasket / cracked head / cracked liner issue that only manifests when the engine is under load, I.e. revving it on the driveway isn't generating sufficient combustion pressure to replicate the problem. Hopefully we'll find out.
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Old 12th February 2024, 22:04   #54
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I admire your resolve to stick at the task mat. Many dont want to bother .. but then again they dont have the lovely colour code yours possesses !! The thing about the bleed method is that although the engine gets up to the stat opening temperature and then you wait until the fan stops on tick over, the radiator lets in pretty cool water. This happens a few times until the rad water temp is much higher when the fan kicks in and causes a lot more turbulence around that stat area. Its more about the operation of the engine at higher temps when you will find any problems with the heads. Dont forget to check the heater both sides for temperatures , that can be a bit tricky to differentiate , as it will in some cases still give out warm temperature on both, but if clear ,should be pretty much equal in good heat output. I have a digital hans temp gauge fitted on my kv6 , and after any coolant change/refill work, i leave mine after bleeding as per mgrover instructions ticking over , and catch the throttle up to around 2500 when the fan kicks in. (this is not stipulated by rover but its just my preferred way) As said it will take a while to bleed out , but the un interupted flow in the tank ,on warm up ,should indicate if you still have air in the system. See how you go on . ...
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Old 12th February 2024, 22:40   #55
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Quote:
Originally Posted by Matt_75 View Post
When bleeding the system the first time, I followed the MG Rover procedure very carefully ...
Hi Matt,

Did you remove the cylinder block drain plug as well as the bottom radiator hose when draining the system?

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Old 12th February 2024, 23:18   #56
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Hi Simon,

Sorry, forgot to mention that bit. Yes, I did. I also cleaned the threads and applied Loctite 242 when refitting.

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Old 13th February 2024, 00:09   #57
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I admire your resolve to stick at the task mat. Many dont want to bother .. but then again they dont have the lovely colour code yours possesses !!
Thank you! It's a learning process for me and I'll make mistakes along the way, but I quite enjoy it. I wish I had more time to dedicate to it (and the other vehicles) but between a full-time job and having two young children, I don't have a great deal of free time. It is indeed a lovely colour and has come close to scrapping prior to our ownership, we (it's actually my wife's car) will do everything possible avoid that fate though.

Thanks for the additional info on the bleeding process. I'll take it for another drive, do the other tests and report back. Based on the behaviour during the 2nd bleeding attempt, I suspect a 3rd attempt will be required...
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Old 13th February 2024, 08:05   #58
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Is this just a matter of varying coolant temperature readings Matt? In other words, is coolant being ejected from the expansion tank cap?

I'm asking because I don't know whether you remember forum member Lida's case. Her temperature was all over the place, usually very high and despite me repeatedly refilling and bleeding. In the end she reported that a new coolant temperature sensor had fixed it.

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Old 13th February 2024, 19:07   #59
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The only time coolant came out of the overflow pipe was during the initial stages of the bleeding process when I had the cap off. The expansion of the coolant and occasional air bubble being released would cause a little coolant to flow over into the annular space around the neck and thus out the overflow. With the cap fitted, I've seen no evidence of coolant being ejected from the overflow.

I vaguely remember Lida's thread, but out of curiosity, will read over it again.

When I changed the thermostat I was faced with the dilemma of whether to renew the coolant temperature sensor or not. On the one hand, the old one seemed to be working okay and changing it introduces another variable, but on the other hand a new one came with the kit and it seemed a good opportunity for some "while you're in there" preventative maintenance. I opted to fit the new one and based on the normal temperature behaviour during the first bleeding attempt, I believe it to be working correctly.

I'm struggling to explain the strange temperature behaviour during the test drive and 2nd bleeding attempt. I thought that perhaps, when the temperature got stuck at 78°C, an air pocket had formed around the sensor and dropping the front of the car back down moved it to another part of the system. I don't know how realistic that is though.
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Old 13th February 2024, 23:15   #60
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I think that the temperature variations you are experiencing around the 80 degrees range ,are quite normal on a stat with around 82 opening. My kaiser stat will stay around this mark on tick over for quite some time ,after start up on idle and driving. Once the stat has opened a few times ,and coldish water no longer enters from the radiator ,the temperature should then settle depending on the journey type and outside temps. Around 84 on journeys average, but rising in traffic up to around 102 when the fan kicks in,and back down to 90/92 It seems that you have a stat insert with a much lower running temperature opening setting than were originally produced. If so ,then it will start to open .before this setting and let in cold water from the radiator especially on tick over. I find this setting fine by me,winter or summer ,but as i am aware its not the optimal running temperature of the kv6 , or economy wise . I have done 25000 miles on these stat temps with no issues , but each to their own... The only other possibility for these temp variations would be an airlock around the temp sender,but i think you would experience massive swings in temp up and down ,rather than sit around the same figure. My guess is the new thermostat could have a low setting insert. My kaiser stat has the 82 degree insert ,by the way.

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