Faulty thermostat... MGF and the dissappearing coolant

[Plezier]

Well it has been a while since I frequented the forums but thought this little issue might be of some interest.

Now for quite a while have been trying to solve a coolant problem and an odd one at that is seems. When using the car the coolant level in the expansion tank drops way down and remains down even when cold until the cap it release then the coolant rushes back up the the correct level???? The car did not over heat although the rad fans did come on more fequently than one would expect and as I said this has been going on for a long time over a year in fact and over several thousands of miles.

Now last Sunday it was a glorious day nice and warm for spring and we started out to drive over to Burghley House for an event there but ......................... about 20 miles into the journey suddenly with no warning the car boiled up!!!! teh car had been laid up over winter a first for us but with a house move in the offing the space on the drive was needed for removing years of junk and the clear out the workshop so away she went to under cover storage my collecting her on the second. I had disconnected the battery whilst she was in store and after reconnecting it and putting in some fresh fuel she fired up first turn of the key and we covered about 120 miles during the week with no issues apart from the N/S/R caliper needed cleaning and freeing off.

Then Sunday this happens ...................... now we have discussed this odd collant problem with several specialists and even showing a couple the reappearing coolant when the cap is released and none could come up with an answer. On Sunday morning luckily the road was quiet and I had water for making tea in the boot so once she cooled a bit the bottle of wayer was added and we turned round and drove the 1/2 mile to a petrol station where more water was obtained and the system refilled as best possible. We then drove home and the temp gauge never got above normal even though the last few miles I really gave her some stick. Normally the oil temp only reaches 90 but on reaching home it was reading 120 so she was HOT. On checking the expansion bottle was very HOT and almost full to over flowing. So I moved my stuff for the day out of the Rover 75 and went over the Burghley to meet those whom we hada arranged to meet with getting there about 1pm at least 2 hours late.

So Monday it was time to see what was going one and on removing the expansion tank it was found to have losts of tiny grannules in the bottom which am wondering if this is remnants of that instant leak fix some idiot previous owner used on her. Now I thought that I had flushed it all through 2 years back when she was fixed up with new radiator and put back on the road but it seems some may have been trapped and now found it's way loose. As it happens I cleaned out an expansion tank only the other week so have fitted that one and will clean out the other one now ready for use in the future!

Firstly I suspected the jiggle valve on the tank return line and yes this was well clogged up so it was stripped and cleaned then replaced. Clean plain water was used to flush the hoses through and then once reconnected fill the system and she was fired up and run up to temp but despite having her running for about 1 1/2 hours the steel coolant pipe from the thermostat housing only got luke warm as did the radiator supply getting a bit hotter the heater ran hot no problem. After this it was becoming clear that the thermostat was where the problem lie................. clogged and blocked I wondered but it seems the actual stat was faulty and not opening unless well above boiling. In fact even in boiling water unless the stat sat on the bottom of the pan directly in contact with the pan on the cooker ring it didn't open. Luckily we had a spare new stat on hand so this has now been fitted with new coolant. After running her up to temp and bleeding the system and having her running for 1/2 hour of so the engine panel etc was refitted then went wentout for a 25+ mile test run and all seems fine but we will monitor the system to be sure as so far the rad fans have not cut in so will keep an eye on that aspect. The new stat is a QH one and with out the little bypass so a hole was drilled in the flange and it is noticable she takes a bit longer to warm up now but of course if the stst is opening now as it should this will be the case rather than having one that is jammed shut. Had thought to do an oil change but on checking it seems that we have used most of our oil stock and also the last filter so now have to get more and do that another day. She is about due an oil and filter change.

I would never have thought a stuck stat couse cause such weird issues ......................oh well you can only live and learn.

[talkingcars]

Pleased it's sorted.

How quickly is the car warming up now?
Obviously running too cool is almost as bed as too hot.

I was surprised to find how much difference in coolant temp there was between oil being at the minimum against the max.

[Plezier]

Took her shopping this afternoon an it was 6 1/2 miles gentle driving, we have no traffic jams on back roads so gentle up to 2000 rpm driving, before the coolant temp reached normal. On the return journey the oil temp needle moved so I might have gone a little too large, didn't measure the drill bit but it looked to be around 1/8" (3.2mm), with my bleed hole. Meanwhile there is no risidule pressure in the system like before and coolant level rises now when hot and drops back to normal when cold as it should.

I plan a much longer run out down into Norfolk hopefully at the weekend that is if Racheal and her hubby can make it and are not too usy to meet up and talk and compare cars will see how she performs on this run out.

[RobboMC]

You have made me feel much better that I fitted a new thermostat in my rebuild. Whilst the replacement engine came with a new stat,
I had no idea how long it had been laying around in the PO garage so I replaced it with a brand new one.

Anyway, my car has developed an interesting noise now that seems to be connected to warming up, hence me posting here.
After about 2-3 minutes of running it gives a loud click. If you put tour fingers in your ears and click your tongue as hard as you can,
well that's about the type of sound it is. For those old enough, it''s similar to the click of a pinball machine when you got a free game.

I'm thinking it could be the jiggle valve popping open, or the thermostat opening in a rush. It seems to be about the sort of time from starting cold
that those sort of things would be happening. Happily, there are no other symptoms, except that the noise was not heard last year.

[Plezier]

Well it is the weekend and forgot it was Easter ................................ not the best time for a run down to Norfolk as the roads are likely to be quite busy with people doing family stuff over the Easter Bank Holiday weekend so will wait until next weekend methinks.

Meanwhile the warm up time seems to be fairly consistant. Popped into one of the local market towns and at around 6 1/2 miles the coolant temp gets to normal on the guage. Am going to get the emissions checked to make sure the overheat did not cook the senders and to make sure she is ready for the MOT in a few weeks.

Robbo bear in mind that the fault stat was only two years old and was bought new from a motor factors 2 years ago!!! Have no idea what your click could be. As mine has the alloy TF 135 inlet manifold fitted I don't think there is a jiggle valve fitted like there is in the polymer inlet manifold. The one on the return to expansion tank I stripped and cleaned.

[Plezier]

Update ................... I kow it's been a couple of weeks but have not until now got further with this.

Now I did drive down to Norfolk and the drive down was uneventful ............................................... however the drive back was another matter! About 40 miles into the return drive she boiled up in the exapnsion tank and engine of course but the rad was only warm. So after every one telling me the head gasket had failed I finally broke down and removed the head only to find a polymer 750 gasket intact!!!!!

What I did find was more of that red grannular muck blocking up water ways again. The jiggle valve, yes it seems the TF 135 alloy manifold has one, was almost totally blocked as was the water way into the head from it. The head itself has no fire ring indentations but as yet have not put a straight edge over it that will come next and after cleaning the block face off and the top of the liners will measure their heights. Will also pull the new thermostat and recheck that to see if it's opening properly.

Am going to pull out the radiator and flush it through as well.

Now what beggers belief is that it's taken 2 years and over 10,000 miles for thsi muck to break free and mess everything up. Just wish I knew what plonker put this crap in the system!!!!

[ArntyR]

Many sympathies Plezier. I feel your frustration.

My own clues were originally a rusty discoloured coolant + tank, hot engine bay + boot area, oil temp around 120degC and a 'burning-coolanty' smell soon after buying my '05 115 MGF/TF. After new cambelt coolant flush I ended up replacing an original img which had previous 'proper' HG repair and receipts. As you point out the black plastic manifold jiggle valve was blocked with coolant system seal too.

After at least 8 clear-water flushes + bleeds, more coolant, new s/s pipes + new radiator, the normal/hot running temp has reduced to 92 - 96degC, the oil temp now peaks around 105degC and long journeys can be undertaken with much more confidence (now monitored by android/torque pro, of course). Most of the flushes kept dislodging an orangy coppery sludge and I kept going until the circulated warm water was clear.

I toyed with checking out the 'stat but prt was out of my comfort zone and I 'crossed my fingers' on that one.

You've definitely inspired me to re-focus on the 'stat (despite the unfamiliarity) if only to 'finish the job'!

Thanks for the update - that's a job finisher, too, and I wish more forummers would provide closure like this.

(Use of this coolant seal in our MGs is, at the very least, no more than a fantasy-inspired, criminal BODGE imo and I'd like a face-to-face with the moron that inflicted it upon me! I have my suspicions...)

[RobboMC]

A radiator shop can easily remove the header tanks and push rods down the tubes to completely unblock it. Doesn't cost much and is
worth the trouble if you are going to remove the radiator then do it properly once and for all.

They will then refit the header tanks and most will even give it a spray of black paint for you if you ask nicely.

[Plezier]

Well the head is off and the gasket was fine. Thought it might have a MLS but turned out to be a normal polymer bead type. The issue was that dratted K-Seal muck that some numpty put in her!!! clogged water galleries in the head so have been cleaning it all up. The K-seal is all over the steel plate of the gasket and thick enough that you can scrape and flake it off in places.

As we had a small oil leak into one of the plug holes have removed the cam carrier to reseal it.

Have also reconditioned the clutch slave as the seal was weeping. Pick up new water pump tomorrow (Monday) along with a top ball joint as althoguh it wa snew 2 years ago the boot had totally perished. Have already removed the old one ready to fit the new on tomorrow.

So we have so far replaced :-

Thermostat (again)
Water pump
Expansion tank cap
Head bolts

The expansion tank has been cleaned out ... again. Along with thermostat housing and steel coolant pipes. Cleaned and checked head and debured, fettled, heads galleries as two of them were tiny. This will increase the flow through the head. Scraped out and scrubbed out the coolant galeries best I could. Have new oil filter and fresh oil of course and fresh OAT to mix up. Need to pull the radiator and get it on the garden hose to flush it through.