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MG Midget and Sprite Technical - Over heating in a 1098 A series?

I have a 1098cc A Series engine and it is overheating – do the water channels have a habit of blocking? I am guessing that with it being such a small engine (1098cc) that they are pretty small and may rust up quick.

The car has the correct temp sender switch (new), 13 blade plastic fan, new 180 degree thermostat and housing and the thermostat checks out), Starts on the button so mixture and timing and valves are dialed in
13lb new cap on expansion tank, new plain on radiator
Radiator was back flushed and cleared before putting in after new water pump
Coolant may be 50:50 – would this give rise to such a high reading??

Any suggestions welcome - I do not really want to take the head off unless absolutely necessary as I do not like distrubing them when they are clearly not leaking.

Thanks

Peter
Peter Green


Under what circumstances is it overheating, after a long hard run or almost as soon as it starts up? Is it actually boiling over or just reading high on the gauge?

Andy
a borris

Hi

After it starts and runs for a short period. I have only let it get to H on the guage as I dont want to damage the engine. The rest of it is good. Car was properly dry stored for 30 years before being reawakened. It also has a new water pump with the slightly longer impellor in it.

Peter
Peter Green

Peter,

A wild guess, do you know the water pump rotated OK when installed with a deeper impellor. I'm not sure about the specifics of A series pump swaps but have run across a case where the pump impellor was sheared off, in that case the engine had frozen but the symptoms sound the same and the owner only realised when the pump was removed, it was a Rover K series rather than A and survived the freezing after a few parts were changed.
David Billington

You might consider pulling the temperature sender and immersing it in a pan of boiling water to see that it is accurate. There are two tiny white dots (usually) at the bottom of the scale; when the needle is between them, it is supposed to be 212F (100C).

Is the thermostat opening? Fairly easy to tell by the temperature of the top hose. Likewise, is the thermostat upside down? Easy to do...
David "keeping my cool today" Lieb
David Lieb


If the pump is frozen (seized) then the rad will stay cool at the top. I'd try dropping the fan belt off and turning the pump by hand, should turn without problem.

Andy
a borris

Thank you all.

The impellor was lightly ground on the rear and clears the cylindr wall OK and has not caught and sheared.

Stat is the right way up and did open and close.

Pump turns freely. I will also look for the dots.

I had been thinking about getting one of those infared heat thermometers - might do a bit more than think about it now.

I will check out the temp sender, but it is new and should be OK.

Any other ideas welcome.

Paul


Peter Green


Just about the only other things left are a collapsed hose or a massive airlock, try reverse filling the cooling system via a heater hose and checking each hose.

Failing that, I'd guess it's head off time!
a borris

You might want to check this is not due to a simple airlock. With the heater matrix set so high it's easy to get air in the system. Although normally this is accompanied with a good deal of banging and thumping as water boils inside the radiator. Make sure the heater tap is fully open and fill the radiator and run the engine with the cap off and burp the system when the thermostst opens by squeezing the hoses. Having the front wheels elevated can help. Replenish any lost coolant that bubbles out and when water stops bubbling up and overflowing replace the cap and fill from the header. If that doesn't fix it the next stage wpuld be removing the core plugs and cleaning out the block.
f pollock

An airlock certainly sounds a possibility.

On reverse filling should I use the hose going into the heater matrix or the one coming from it please?

Presumably the radiator will fill with the thermostat in it even if it is closed as the water will fill the radiator from the bottom?

Sorry if this sounds rather obvious but I have never attempted this sort of a reverse fill before.
Peter Green

Have you tried running the engine with the head to heater pipe removed (remove from heater end!) to check the flow?

To back fill the system use the highest pipe on the heater, remove the the thermostat and stop when the water comes out the thermostat housing, replace thermostat and add anti freeze into the rad, then continue till the rad and expansion tank is full.

Replace the rad caps before removing hose and replacing heater pipe, this will slightly reduce the loss from the heater as you do it.

Andy
a borris

Peter, Check your exhaust system and make sure it wasn't a home for rodents for the last 30 years. Nests inside the tubing will build heat back into the engine fairly rapidly. Another non water issue could be the oil system. Years ago I had a 1 3/4 bearing 1098 that went way hat after short runs. Turned out to be a crack in the pick-up tube in the sump. She'd satrt sucking air when she warmed up and not get enough oil to the block. Lastly do a compression check on the cylinders. The 1098's were famous for blowing out between the 2 and 3 cylinders due to the side by side exhaust valves. Could possibly be pushing steam in that area. Just a few alternitive ideas.

LaVerne
LED DOWNEY

Well I eventually decided to bite the bullet and pulled the head off.

The holes were totally plugged up, so I think we have got to the bottom of this now.

Thanks everyone - some interesting ideas!

Pete
Peter Green

This thread was discussed between 25/08/2008 and 31/08/2008

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