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MG Midget and Sprite Technical - Coolant problem

Hello all.

My 1275 Midget has been laid up for 5/6 weeks due to ill health.

On Saturday I charged up the battery & checked coolant level. I noticed a drop in the rad level of about 25mm so topped the rad up. I could not find any tell tale signs of escaped coolant. The expansion tank was at the correct level about half full. I tightened all the hoses up.

On Sunday prior to taking to the road I checked the rad again. I had the same results as Saturday. I ventured out & chose to drive locally only.

The heater tap was left open & the interior warmed quite quickly as normal - I have the mechanical fan removed & fitted a Revotech thermo fan. The water gauge did not reach it's normal (for this gauge) level half way between Cold and Normal.

The thermo kicked in at a lower level than I would have expected. The ran fine and showed no rough running due to overheating. I cut short my run.

This AM I took another look. Again the coolant in the rad has dropped. I then checked the expansion tank & this overflowed with coolant.

Is this a blockage requiring a good flush?

Any thoughts would be appreciated.

Gavin




Gavin Rowles

Stuck thermostat perhaps? Does the radiator actually get warm? This doesn't directly explain the loss of coolant but might cover some of your symptoms depending on where your fan switch is positioned in the water circuit.

Easy to whip it out and check, visually to see if there is any rust or gunge and then by boiling in a saucepan to check that it actually opens.

Otherwise if coolant is not escaping outwards it must be going in. Remove spark plugs and check that they are not rusty, and keep an eye on the oil level in the sump make sure it is not increasing.

Happy New Year.

AdrianR

ETA: Adrian posted whilst I was still typing - I don't think there is necessarily any problem (with the coolant at least).

Gavin,
I don't know why your 'water' stat appears to be opening at a lower point on your gauge - but - as far as coolant level goes stick with how the Driver's Handbook tells you, check the level in the expansion tank.

If you check at the radiator then the level will be lower, and if you then remove the pressure cap the coolant will go from the rad to expansion tank and could overspill.

Follow the refill instructions from the Driver's Handbook (see below).

If you want a simple but thorough method of cooling/heating system cleaning (or more thorough method) I have one but I'd wait until the warmer weather before doing so as cold water is very cold this time of year.

Hope this puts your mind at rest about the coolant level at least, if the 'water' stat is opening and the car is running well it could just be that the air going through the rad is colder or that you've done something to help the rad with its cooling (brushing rad, removing obstructions like leaves or rally plaque(?)).


Nigel Atkins

It's posible that you have a bit of an air lock in the cylinder head. If this is where your sender unit for the temperature gauge is, then it could "high and dry" and be measuring an air pocket rather than water temperature.This could be why it is showing lower than normal.

As Nigel says, once initial filling is completed, then leave the rad filler plug tight and finish off filing via the expansion tank. To clear a possible air lock, once the coolant in the expansion tank is over the end of the internal pipe (i.e. about 2/3rds full, then reach down and give the large lower coolant hose, the one near to the near side engine mount, a few good squeezes. This should pump fluid and any air bubbles out into the tank and then as you release it, it will suck pure coolant back in. Squeeze and massage the pipe a few more times. making sure that you keep the expansion tank topped up so it doesn't pull air in and that should clear any air lock.

Err on the side of overfilling the expansion tank. It will discharge any surplus and settle to its own level. Don't remove the expansion cap when it is still warm. Partly the risk of scalding if it is very hot, but mainly because as the coolant cools it will contract and top itself up by drawing from the expansion tank. If you release the cap when it is still warm, then this self filling process won't work.
GuyW

If it's not getting up to temp then 1st port of call is the thermostat
Most thermostats now, when they fail, they fail towards cold---years back they failed hot which caused boiling
BUT
The issue of low coolant and full overflow bottle can be caused by the cap not sealing properly, if you go to your local radiator joint they can pressure test it-and make sure you have the right cap
OR-
-and I hope not for your sake, it could have the start of a headgasket or cracked head issue, this will allow air bubbles into the coolant and cause the coolant to be blown out into the tank and can cause the gauge to read low from lack of coolant to sense
If you get the car up to temp with the cap off and then leave it running, top the coolant right up and watch it, for a couple of minuites there shouldn't be any bubbles in the filler neck, if it's ok
Good luck
willy
just had a thought--------
With your system is the pressure cap on the radiator or on the expansion tank
William Revit

Hello all & thanks the advise.

I'll check out all these suggestions.

Adrian - I will remove & test the stat.
Nigel - the guage fitted new by me some years ago has always read low. It is
consistent to date so I feel reliable.
Guy - I'll check for an air lock.
William - I will check the cap seating. I have a spare to try anyway. The pressure cap is on the expansion bottle.

Bit warmer today so hope to look at later.

Gavin Rowles

Gavin,
be interesting to see the results of a run today if its as warm as here today.

All the C-N-H gauges I've had have read low, so as you say as long as it's consistent in its reading (though that doesn't suggest that they are necessarily that accurate in that reading).

I look for 5 passed 7 on that gauge when running normally.

I thought you meant the 'water' stat opened earlier than you expected by - "The thermo kicked in at a lower level than I would have expected" and you put "The water gauge did not reach it's normal (for this gauge) level half way between Cold and Normal" so I thought the 'water' stat is opening but at a lower reading than you expected. If the stat is stuck open or doesn't fully close then the car will obviously take longer to warm up and could run at a cooler reading particularly on cold days.
Nigel Atkins

To recap
If the thermostat is opening early, then it will run cooler and your fan coming on early is caused by the thermostat opening early allowing hot water into the top hose/tank early where I guess your fan sensor is
located
Bit worried about the coolant level though--
With the pressure cap on the expansion bottle, the cap won't be causing the level in the rad. to be low--There's (hopefully) an external leak under pressure there somewhere, hoses, radiator,pump-heater core
OR a blowing headgasket / cracked head
You will have to do a bubble check at the radiator (not the bottle)or get your radiator joint to do a chemical check of the coolant for combustion fumes
William Revit

Gavin,
There are two lengths of pressure cap. Check yours is correct when measured against the depth of the neck of the expansion tank.

Also one can do a reasonable quick check of it, without removing the thermostat. Start the car from cold, allow it to idle and put your hand on the top hose. (Mind the fan!) It should remain cold for a few minutes and then quite suddenly heat up and become warm to touch as the thermostat opens. If it heats up steadily from cold then it is likely sticking open. If it remains cold even as the engine gets hot, then it is sticking shut.

You are looking for a definite and fairly rapid warming of the hose 2 or 3 minutes after starting from cold
GuyW

The first thing to check from your description of the issue is the hose from rad to expansion bottle and the bottle itself.

When the engine warms up the expanded coolant flows from the rad to the bottle, after switch off the engine cools and the water is sucked back in from the bottle to the rad - if there is a problem with hose or bottle then air can get sucked in instead which is what you are experiencing.
Chris at Octarine Services

Hello all.

I've been through all the suggestions.
Checked both the stats I had and both opened as required.
I bought a new expansion bottle cap as the current one looked a bit suss.
I have purged the hose for air locks but found none.

This PM I took the Midge for a ride. I kept the heater closed for this run. The gauge showed a little higher than normal & again the Revotec thermo switch came on earlier. The engine ran fine. On my return with the bonnet lifted water was being forced out of the thermostat housing - in the last 2 weeks I had replaced with a new Klingerseal gasket.

I think I may need to flush the whole cooling system which I hope will clear or have an air lock. Nigel - please advise your method.

I'll start by looking at the expansion bottle to rad though.

WR - not tried your bible test yet. Hope it does not come to HGF or a cracking head!

Continued thanks

Gavin


Gavin Rowles

Hi Gavin,
my "method" is only a simple but thorough (and more thorough) cleaning of the cooling/heating system, it may help you discover issues or the issue (or it might not) but you might be better doing more investigations and taking advice whilst your system is still filled. Certainly do the bubble test at the rad Willy suggests.

If you have to drain down the system or part of the system and you haven't previously done the thorough cleaning I suggest then it may be very well worth doing.

Email me and I'll gladly send you my three-page Word.docx of the very simple, unoriginal but thorough cleaning.
Nigel Atkins

Coolant coming out of the thermostat housing if it wasn't happening before may be an escalation of the current issue or just a case of the housing not fully sealing this time for various reasons.

I know it's a lot easier to be optimistic when it's not you and your classic with the problem but with caution you're unlikely to add to the problem so and you will be able to resolve it regardless, hopefully quite easily.

All the best.
Nigel Atkins

Most garages will have a probe that, dipped into the header tank, will detect combustion gasses in the coolant if there is any head gasket leakage.
A friendly local garage, if you have such a thing, would probably do it for free - it costs them nothing other than a few moments of their time.

Or do a compression test - testers are available on eBay for around £10 and makes a worthwhile diagnostics addition to your toolkit.
GuyW

Something like this. Cheap and nasty by professional standards, but if you are not earning a living with them it is perfectly adequate for DIY use.

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F282461453989
GuyW

Good idea (I'd forgot).

"friendly local garage" I've no idea what it's like in East Sussex but I wouldn't know where to find one round here.

But for a fiver you can get combustion gas kits, or go for dip tabs, for yourself.
Nigel Atkins

Hello all.

Today I hope I have been able to resolve this problem.

I have not been able to identify the exact cause but over the past 2 weeks carried out the following:-

Full flush in both directions through both the heater box & engine with the thermo removed (though as I have a standard bypass I'm not sure if this was necessary).

Check for gunk at the engine block drain.

Examined all hoses for wear plus tighten each clip & replace as required.

I've refilled with 50% rainwater & 50% new blue antifreeze.

The were no bubbles ro be seen in the rad as it warmed up.

Revotec now kicking in fine.

My best guesses are:-
Leak at 1 or mote clips hence the fall in rad level
An air block. My research elsewhere recommended reverse flushing.

Anyway - back on the road - a Fish & Chip run beckons!

Gavin.




Gavin Rowles

Gavin,
great, well done.

I've used this reverse-flushing malarkey through the heater matrix, engine block and rad to good effect myself.

I'm not sure, now, that you need worry about rain water as tap with it's impurities might even be better, but 50% antifreeze is more likely to find small weeps and leaks so if you don't have any that's good.

Also at 50% you're protected for lower temperatures so you can go out and enjoy the car to greater windchill factors (not that we've had any recently).

I've never had an airlock following the instructions in the Driver's Handbook.

I had a great drive today and a couple of other times this week in sunny and dry conditions, but I must admit to keeping the roof up, I'm now old and feel the cold more.
Nigel Atkins

This thread was discussed between 06/01/2020 and 29/02/2020

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