Bizarre overheating coolant loss issue. - MG-Rover.org Forums
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post #1 of 23 (permalink) Old 04-02-2017, 11:00 Thread Starter
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Bizarre overheating coolant loss issue.

So the MGTF I bought at rock bottom had a proviso that it was overheating.

So I went through the system with a fine toothed comb.

First of all the inlet manifold gasket was replaced as half the bolts were only finger tight.

Then I found one of the plastic T-joints had split so was loosing pressure and I replaced that with a brass fitting.

Then I replaced the cap.

Then I bled the system ...TWICE.

This seemed to get rid of everything.

What the symptoms were, and still are, is that the stat sits around 94C on the motorway after a slow warmup (only a few minutes).

But then if I'm driving above 70 for any extended period of time it will sometimes shoot up to 120 and vapour lock.

At that point I'm having to add around 1-2 litres to refill.

Now this indicates to me either the cap is not working (it's brand new), there's an air leak somewhere causing pressure loss, another coolant leak somewhere I can't see, and/or the PRT is knackered.

After bleeding I can rag the car to pieces and no overheating but it seems to happen after about 1-2 weeks of long distance driving with no obvious signs of coolant loss in the tank.


Any ideas? I'm guessing another possible corroded plastic connector or a sludged up radiator causing insufficient cooling.

I have yet to flush the coolant system and replace the PRT (which I have a spare for already), and I really don't think it's HGF for various reasons, though it will end up happening at this rate through heat cycling if I don't sort this issue out.

Are there any common but difficult to get at areas of leakage (the under pipes look fine to me)
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post #2 of 23 (permalink) Old 04-02-2017, 11:34
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I'd start by replacing the cap with an OEM one, checking the rad fan cuts in and re-bleeding (using the high bleed screw). See where you are then...

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post #3 of 23 (permalink) Old 04-02-2017, 14:31 Thread Starter
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Originally Posted by gnu View Post
(using the high bleed screw)
What do you mean by that? You mean the engine bleed?

I should also mention the times I bled the front two there was around a litre of air from the heater matrix before it started flowing coolant.

A fair few bubbles in the radiator also. I know you're supposed to bled all three but would the rear one really be causing that? It's almost impossible to ever get that one NOT to flow air out of.

Only reason I didn't the 2nd time was the cover was on but it was fine the first (my burnt hands are testament to that).
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post #4 of 23 (permalink) Old 04-02-2017, 15:21
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Originally Posted by Stargatemunky View Post

Only reason I didn't the 2nd time was the cover was on but it was fine the first (my burnt hands are testament to that).
It's essential to do the one in the engine bay. It's the highest one in the system. If you are still getting air from that one there is still a problem somewhere.
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post #5 of 23 (permalink) Old 04-02-2017, 19:21
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Also make sure that the heater temperature control is on fully, even if it looks like it is in the past it has been found that the control isn't turning the valve on fully.
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post #6 of 23 (permalink) Old 04-02-2017, 20:18 Thread Starter
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Heater is always on, rear bled tap was flowing fine (when I did it the first time, so...meh).

Just have to flush the whole system and swap the radiator out for the one I've got lying in the garage...because might as well...

I have no problem keeping going until the problem is solved.

is 94C a normal temperature for the TF system, as I've found my other cars tend to hang around 78-86C. Wondering if that's normal and might also indicate poor circulation of coolant.

The heater works fine btw, except for when the coolant has boiled off and i'm running on 8 litres only.
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post #7 of 23 (permalink) Old 05-02-2017, 08:16
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If you've checked out the above, try parking on card after a run. Check before and after journey's for signs of leaks. Sometimes, due to heat expansion/ pressure they only happen when cold or hot...

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post #8 of 23 (permalink) Old 05-02-2017, 08:49 Thread Starter
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Yeah, I want to hook up a foot pump so I can pressure test it for just above 1.1bar in case it's only happening near the limit.
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post #9 of 23 (permalink) Old 05-02-2017, 08:56
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Don't forget to check the radiator- often overlooked due to its location.

The favourite leak spot seems to be the bottom left corner for some reason (when viewed from the front).
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post #10 of 23 (permalink) Old 05-02-2017, 13:06 Thread Starter
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Well it's all bled about 15 times, from all 3.

As I was doing the transmission fluid I thought I might as well do all of it.

We'll see how things get on though i'm going to be flushing the entire system in two weeks time anyway and we'll see if any dead mice fall out.

Interestingly enough my transmission had a left over plastic stopper inside from one of the old bottles the previous owner had used. No idea how it had managed to survive so long in there but there was barely 2.2 litres of oil in it.... the rover bare minimum they like to quote.

Also ordered another 3 caps to be sure I have spare. Because reasons.
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post #11 of 23 (permalink) Old 05-02-2017, 23:33 Thread Starter
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Well the issue is still there, it's still struggling to handle the temps of anything above 98 degrees and just spiking once it hits 100 and going up and up.

Interestingly it handles the temperatures more consistently with the heater matrix locked out so I strongly suspect it's a pressure issue with the radiator not flowing enough.

A PRT replacement and system flush will resolve it once and for all.
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post #12 of 23 (permalink) Old 06-02-2017, 10:54
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Originally Posted by Stargatemunky View Post
...... my transmission ......... but there was barely 2.2 litres of oil in it.... the rover bare minimum they like to quote..
Not sure I understand that - 2.4 litres is quoted as the correct capacity of the PG1 for a dry fill (ie. a new or reconditioned box being filled with fluid for the first time). The figure they quote for a normal PG1 fluid change is 2.2 litres, which is what you have drained out.
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post #13 of 23 (permalink) Old 06-02-2017, 20:13 Thread Starter
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Most people realise 2.2 or 2.4 litres is nowhere near the actual fill level for the PG1.

There are various rover mechanics out there that recommend around 3 litres for the refill.

2.4 is the bare minimum. It's like filling up your engine with 3.5 litres instead of 5 litres 10w40.

I put about 2.8 litres in mine
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post #14 of 23 (permalink) Old 06-02-2017, 22:39
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The amount specified by Rover is the correct amount, and will be sufficient to bring the oil up to the level plug - there is a clue in the name 'level plug'

The PG1 is actually a Honda designed box, which they licenced to Rover - are you suggesting the Honda designed the box to be underfilled?

There is also the not insignificant matter that the PG1 has been used in a wide range of Honda and Rover cars, and in almost every case where there has been an unexpected or premature failure, it has been due oil leaking and leaving the box seriously short of oil. You don't hear of such failures where the oil level is kept topped up to the manufacturer recommended level.

...And, no - it isn't like putting only 3.5 litres in your engine instead 5. It is like putting 7.5 litres in the engine.

I think any idea that the PG1 needs 50% more oil than it is designed to run on is another of those myths that has grown up over the internet, based on nothing at all. It is no different from the peculiar idea that coolant loss from a sealed system is normal
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post #15 of 23 (permalink) Old 09-02-2017, 00:11 Thread Starter
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Originally Posted by Man in the Car View Post
there is a clue in the name 'level plug'
There is a clue in the basic laws of physics where 2.2 litres doesn't bring the level of the oil up to the level plug.

The instruction manual says use 10w40.... Rover then changed that to MTF94 despite the gearbox never changing it's atomic structure in any way.

Rover's have never had any design problems through cutting corners.....EVER... HGFs just don't happen and it's a conspiracy by Honda to sell more Hondas.

That is all I have left to say on the matter.
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post #16 of 23 (permalink) Old 09-02-2017, 09:28
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Very odd - when doing a transmission oil change on my ZR (which is also a PG! gearbox), I found that the recommended 2 litres was ample (for some reason the recomended amount is 0.2 litre less for the ZR than for the TF; probably because of differing gears/differential, or possibly gearbox orientation) - oil was running back out of the level hole, so it was certainly up to the level plug. It is possibly worth pointing out that if the car is not reasonably level (ie. jacked up at one end for access underneath) this will significantly effect where the recommended quantity of oil come to in relation to the level plug

The oil that Rover recommended has changed a couple of times, and it is true that 10W40 engine oil was the recommended oil at one time. This was changed after they concluded that some gearbox problems that were surfacing were possibly related to the oil type, so they changed the recommendation to a more usual gearbox grade oil. The final change to MTF94 was done simply to enable them to extend the change interval to over 100000 miles from the previous requirement to change the gearbox oil at about 30000 miles. The MTF94 is simply a long life version of the previously recommended 75W80.

The fact remains that when a PG1 experiences problems, it is virtually always because there has been an oil leak and it has been run with little or no oil in it. There are rarely problems where the oil level is kept to the recommended amount.

Having been around Rover forums for nearly 14 years, this is the first time I have seen anyone suggest that the quantity of oil recommended by Rover is insufficient for the PG1

I don't understand the rather odd comment regarding a conspiracy by Honda - the same design of PG1 gearbox was used in a great many Hondas, with similar recommended oil levels and they didn't suffer as a result. Wherever the story of needing to overfill the PG1 has come from, I think it comes down to what could be classified as 'pub talk' or perhaps one of the more recent 'internet myths', or maybe a 'facebook fail' (some of the absolute twaddle that gets accepted as fact on facebook has to be seen to be believed!).
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post #17 of 23 (permalink) Old 09-02-2017, 10:32
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, or maybe a 'facebook fail' (some of the absolute twaddle that gets accepted as fact on facebook has to be seen to be believed!).
You sure got that right. Some twaddle on some forums too.
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post #18 of 23 (permalink) Old 13-02-2017, 17:29 Thread Starter
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So it looks like the split hose had caused the engine to overheat.

This in turn has caused the Radiator fan to burn itself out from overuse.

So the coolant is replaced and the radiator too (just for *****s and giggles)

Will end up fitting a remote stat at some point as i'm fed up with the high average engine temperature the PRT gives to begin with.
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post #19 of 23 (permalink) Old 13-02-2017, 17:32 Thread Starter
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You sure got that right. Some twaddle on some forums too.
Source was here: MGF MG TF PG1 manual gearbox oil filling

Not exactly what I'd call a Facebook post.
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post #20 of 23 (permalink) Old 13-02-2017, 17:39
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...

Will end up fitting a remote stat at some point as i'm fed up with the high average engine temperature the PRT gives to begin with.
Can you explain what you mean? I modded my Steppy with a PRT mounted up front and had far better temperature control as seen on my Scangauge. Not high at all and I wouldn't expect a standard PRT down the front of the engine to run high temperature either. Are you sure there isn't a standard stat in the engine too? (May have missed that bit if you've already said it is removed)
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