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MG Midget and Sprite Technical - wont idle after running hot

Hello.
I'm having trouble with my 1979 MG midget 1500 - it wont idle and cuts out as soon as I ease off the accelerator when stopping (ie not while driving, only when rpm gets below 800). Power also seems to be decreased when driving/accelerating.
Recent history: it has been very hot the last 2 weeks, 35-40C (95-105F). The temp gauge had been reading between quarter and three quarter, generally rising above half when stopped in traffic and coming back down once moving. I believe this is due to inadequate fan (original fan belt powered, not electric) and undersized radiator (?). The radiator was fitted by my specialist MG mechanic but is only approx. 40cm x 30cm x 5cm.
Anyway, 2 days ago I set off for work and after only 5 minutes driving the temp gauge passed the three quarter mark. I immediately pulled over and turned off the engine. Once cool, I discovered that the radiator was very low. It seems that the lower radiator hose is a different diameter than the radiator outlet, so the mechanic had put another hose inside the main hose to effectively decrease the diameter and fit to the radiator. This inner hose had moved further within the outer hose and allowed the coolant to leak.
I have now fixed the leak and filled the radiator with coolant but cannot get the car to idle. I have checked choke lead and accelerator cable and can't see any problems there. Any ideas?
Is it likely that the inlet manifold gasket has split/blown due to the high temps? At no stage did the temp gauge rise above 3/4, so I would think unlikely. How do you test this?
S Travis

hello mate

i see what your saying, my engine had the same type of problem. when i start mine ( even on a warm day ) i have to rev the engine for a good few minutes just to get the engine hot enough then i ease off and the revs stop at 1500.

joe
jc collins

ST, I am sure others will contribute more fully, but overheating can cause cylinder head gaskets to fail which can cause all sorts of symptoms, such as not idling etc.
Though you say you lost a lot of coolant the gauge didn't go above 3/4?
Of course these gauges are not very accurate and the engine could have been extremely hot in reality.
Your mechanic would be able to do a compression test to check if there is any lack of integrity at the top of the cylinders.

Joe, is your choke working OK?
You should be able to keep the engine running until warm enough by adjusting the choke position as required, rather than just revving the engine to keep it from stalling.
JB Anderson

Im not familar with the 1500, But if you lost alot of coolant, whats the temp sensor supposed to read... hot air? :)

well okay maybe steam not hot air...So Im with JB, in guessing you toasted the head gasket

BTW... You need a new mechanic, prefably a british classical. He sounds a little to much like me, doing stuff like this is okay for me to do on my car, but if i were a mechanic with any self respect, Id do other peoples cars correctly.

If you do need a new head fasket, Id certianly put back in the orginal rad made for the car, these rads from the factory where just barely acceptaable in hot temps with pure stock cars (pending the enviorment), So going smaller is not a diretion Id go, at least not without extensive expensive modification
Prop

The mechanic is supposedly a mg specialist and was recommended by several. I had an issue with the car getting hot in traffic a couple of months ago and had the mechanic have a good look at it. He moved the fan closer to the radiator (using spacers) and checked thermostat and pump etc. (all of which were new when the radiator was replaced, 9 months ago). He also advised that the temp gauge reads higher than actual temp compared to his infra-red temp gun, and said that close to three-quarter mark was quite safe. This is why I wasn't overly concerned with temps between half and three-quarter.
I also had the same mechanic do a lot of work on the cylinder head at the same time that the radiator was replaced (new valves, hardened seats, ports matched, cam grind). I guess I should go and confront them but now I am worried that if I get them to fix head gasket (if needed) because they caused the problem, it should be free but they will either do a bad job or expect a lot of money again!
S Travis

Is it possible the thermostat and gauge were reading the boiling point (steam) of what was left of your (unpressurized) coolant/water mix and the actual temperature around the cylinder walls etc. was much hotter? Although you say you caught it quickly.

The usual spray products used in the region of the intake manifold/carbs and I.M./cyl. head might tell if you've developed a vacuum leak there since overheating.

FWIW my California spec 1979 1500 always ran at 3/4 gauge or hotter before removal of the catalytic converter and timing retard, I never had any manifold or head leak issues I was aware of.

I have to say hose-in-hose is not a solution I would have wanted to pay someone to come up with, MG specialist or otherwise. I suspect that "MG specialist" is beginning to mean "The only guy left around these parts who can stand working on them", whether Down Under or here in Sunny California, or Elsewhere.

Have you checked you valve adjustment since running in the cyl. head work? Pretty common to need a tweak a few miles after the kind of work you mention. If it's breathing better due to the porting work might the air/fuel mix be leaner and contributing to the hot running? An external air feed to the carbs might help a bit.
Richard Reeves

S Travers... where in Aus are you....?

I'm sure I can help you if you are close to the GC....

Mark.
M T Boldry

What do you mean by "the usual spray products"? Is it like WD40/RP7 etc?
I don't have an external air feed, just ram tubes with foam sock filters. It is certainly breathing better, also had extractors/headers fitted with straight through exhaust and single rear muffler (Super Cat). I have had it adjusted after a "run in" period.
Generally, it doesn't run hot and the temp gauge does not rise above one-quarter, even on a recent 600 mile trip in 30+ degree Celsius weather - it is only when stopped in traffic.
I see your point about the gauge not having water to temp, and the head being hotter than the gauge. Its been 5 days without driving it - I am starting to get withdrawal symptoms!
S Travis

sorry Mark, missed your post. Would love your help but I'm in Melbourne!
S Travis

This thread was discussed between 05/02/2011 and 09/02/2011

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