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MG Midget and Sprite Technical - I'm overheating - so is my Midget!

I'm not quite at my wits end but I can see them on the horizon so I'm hoping somebody can suggest something I've missed.

Background: no overheating problems in many years (including several track days) until after a day at Silverstone in March I had a sudden overheating on the M42, didn't stop soon enough and had a valve seize in its guide. No water found in radiator (despite it being full earlier in the day) but can't figure out where it went (but guessed it was head gasket failure).

Now: engine rebuilt with new cylinder head. Just been for two runs of around 15-16 miles each and on each occasion it has started overheating again (needle up to 'H' on the gauge). I can't understand this as the ignition setting is unchanged (so not retarded)and the carbs unchanged (so not a lean mixture). I can't find any leaks in the coolant system (I had radiator checked professionally and was OK, fitted a new radiator cap and system is fully pressurised and checked all hoses and clips).

What's left that might cause a sudden change to overheating? It was 24 degrees in the sun but that should not have this effect. The only thing I can think of now is a faulty water pump but these don't fail suddenly do they? Any wise words gratefully received.
Chris Hasluck

yes pumps can and do fail; the pressed tin impeller can come loose on the shaft so it no longer turns and the water is not circulated. For the sake of 4 bolts and a new gasket it needs to be checked.
David Smith

David
I've got a Metro pump with a deep cast impeller but you are right - I need to check the pump.
Chris Hasluck

Run the engine up to temperature with the radiator cap off and see if the coolant is moving. Or when it gets warm, see if the radiator is hot top and bottom. If the top is cooler then it might be the thermostat not opening. Much easier and cheaper than the water pump.
Martin Washington

the cast impellers don't usually give any problems.
David Smith

The thermostat is new and I tested it prior to fitting.
Chris Hasluck

Chris. In what way was the radiator professionally checked? Exactly what did they do? Just pressure test it?

You can have no leaks at all, and still have a problem. I suspect the rad is partly blocked, obstructing flow.

Have you tried all the usual flushing routines? Do you have another rad to bung in for a test?
Lawrence Slater

Hi Chris,
What Lawrence says...
Whip the radiator off (Lawrence will tell you how to modify it to be quick release) and flush it both ways. You could even put battery acid, vinegar or coke in it to get it sparkling inside. Remove the bottom pipe and clean that too, just in case.
Take the pump off to check that the impeller is still in tact.
If not a new one is cheap -
http://www.minispares.com/product/classic/GWP134EVO.aspx

Also check that there is nothing blocking the fins of the radiator. Leaves, bugs and general rubbish collect on the front face of the radiator.
Do you have enough air flow through the radiator?


good luck.

Dave
Dave Brown

Also try flushing the engine through both ways....
it could be that some accumulated crud/rust has dislodged and is blocking the waterways....

its amazing how much will come out....
Andy Phillips (frankenfrog)

The radiator specialist said the rad was OK both in terms of leaks and flow rate so should be OK.
Having said that, he described the rad as 'Serck rubbish' saying it only had two cores (cheap) and offered to rebuild it with three cores.

Perhaps I should have taken up the rad rebuild offer (around £100) but as I've never had any problems in 12 years I am puzzled as to why now and suddenly. I'll try flushing everything and have just bought some BARS flush and will try that before pulling the pump.
Chris Hasluck

Is your gauge goosed? Are you genuinely overheating?
Mark O

My sprite overheated with 100% coolant. 50% water solved the problem. Do you use coolant?
Flip
Flip Brühl

I use 50/50 water and anti freeze. Gauge is probably OK - it certainly was when I broke down!!
Chris Hasluck

Chris my '73 midget is 2 row. Runs cold, even on a warm day. I'd say you have a blockage somewhere. Maybe as suggested, it's in the block.
Lawrence Slater

Is there any water loss? is the overheating caused by an HG failure? I know you replaced the head, was the block nice and flat? Are the compressions the same for each cylinder?

As mentioned it could be a blockage in the block, Does yours have the tap/drain at the rear of the block behind the manifolds? does coolant run freely from there when opened /removed. The original overheating problem may have dislodged rust and crud which may be a problem. Taking the pump out also gives a bit more of a clue on the condition of the block.

Bob Beaumont

Was the h/g blown when you stripped it down originally?
Jeremy Tickle

Hi Lawrence. I've never had any problems with this radiator in 12 years so it should be capable of dealing with my engine. The problem must be elsewhere.

Hi Bob. No coolant loss this time.

Hi Jeremy. No obvious sign of HGF when stripped down. The engine was running fine until the valve seized and even then it was running OK (because the valve was opening and closing because the guide was loose). It remains a mystery as to where the coolant went. There was no trail of vapour behind me and no steam under the bonnet. I assumed HGF but it could be the radiator cap was not working well and allowing coolant out.

I'm in the process of flushing (the car) as I write.
Chris Hasluck

No trace of oil in the water then if the HG was ok - could it have anything to do with the heater matrix/connections?
Jeremy Tickle

Hi Chris. I agree, 2 rows should be enough, that's the point I was making.

The way I see it. Either,
1)Your engine is overheating due to an engine fault, that the radiator, even though good, can't cope with.

-- Or ---

2)Your engine is overheating because the rad can't cope with the normal running of the engine.

You say the engine is running properly now, and there are no water leaks. That leaves an obstruction, in either the engine, the heater, or the radiator.

Bi-pass the heater matrix. Run engine and see if it runs at normal temp.

If no change, you may have an obstruction in the engine, or the radiator.

Your radiator may have been fine for 12 years, but that doesn't mean there isn't an obstruction now. Do you have a spare rad to bung in as a test?
Lawrence Slater

This is of interest.
http://www.calverst.com/articles/Cooling-How_it_works.htm

Here's an interesting quote from it.

"Anti-freeze is widely used as an additive to water in car cooling systems, ----- " ---- " It does not, however, increase the cooling capability of the system. Many people are under the false impression that adding more anti-freeze will solve over-heating problems - nothing could be further from the truth."



Lawrence Slater

All anti-freeze does is just what the name implies, keeps the coolant from freezing. It doesn't cool better than water.

The world of high tech automotive racing, Formula 1, uses nothing but water as a coolant because it's the best thing out there. Since they don't drive in extremely cold temperatures they don't need anti-freeze to gum up the works.
Martin Washington

Hmmmm, so the hi-tec world of F1 doesn't see the benefit of the miraculous properties of this new stuff such as Evans Waterless Coolant?
Hmmm, wonder what conclusion can be drawn from that?
David Smith

I think everyone knows my views on waterless coolant :) However even though water takes away heat better than anything else....it may well be the case that race tracks around the world do not permit anti freeze as it is flammable so it cannot be used anyway! I still think F1 folk know that water is best!!!

I agree with folk for the Midget, just try neat water and see how it goes, put antifreeze in for winter if necessary.

Peter
Peter Burgess Tuning

You asked Where did the antifreeze go ?

Did you install new hoses before the rad ran dry?

If so ... Bingo !

I dont know why this is, and it maybe something im doing, but when I install NEW rad hoses I have to always go back and retighten them with in 100 to 200 miles,.as they will leak ever so slightly and not even noticable untill its empty

Its only on new hoses at there connections

Prop

Prop and the Blackhole Midget

As well as stopping freezing anti freeeze acts as a corrosion inhibitor.

As you have rebuilt the engine I wonder if the problem now is just an air lock.

Trev
Trevor Mason

Now here's a puzzle. I've just done a run with no overheating (needle on 'N' throughout). What's changed? I retarded the ignition. Yes, retarded! I have a 123 dizzy and normally set it to advance curve No5 but just remembered that when I put the engine together this time I tried a little more mid range advance by setting the dizzy to advance curve No6 (as suggested by others on this BB archive). Having remembered that change and reversed it I seem to have got rid of the overheating. Yet all the manuals and advice say retarded ignition = overheating and advanced reduces overheating provided there is no 'pinking'.
Anyway, this might be a fluke and only a few more road tests will prove whether I've sorted matters but it looks promising.
Chris Hasluck

congrats... I.wouldnt question the gods on this one, just enjoy it
Prop and the Blackhole Midget

Chris

Apologies. Severe case of not reading the initial post properly. I had similar when adjusting the ignition only very slightly, so I can at least corroborate your findings that a seemingly very slight adjustment can affect the coolant temperature quite significantly. For me, I too found curve 6 worked well, and since Metro head swap, curve A. Useful link below.

http://www.mintylamb.co.uk/123ign.html

Another possibility could be crap in the carb jet causing the engine to run weak and then subsequently hot. Since you do not appear to have it now, it may have passed through, but a squirt of carb cleaner and a drain of the float bowl may prevent further mishaps.
Mark O

This thread was discussed between 12/07/2015 and 16/07/2015

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