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MG MGB Technical - normal operating temperature

could anyone tell me that the normal operating temperature for a 1970 bgt? the ambient temp is around 30 deg.C in HK and the b is running at almost 94 deg.c.
if there is traffic, the temp goes up to 100 deg.c.

also, the idle seems a little rough even though i put a new distributor, spark plugs & lead, coil..... and when the temp goes up to 100 deg.c, the idle drops under 500rpm and sometimes even stop. (the engine is tuned at around 80 deg.c)
ennio wong

Ennio, there several factors which would affect what I can advise you to have a look at.
Firstly I am assuming that you don’t use anti freeze. I also don’t know what pressure cap you are using. Assuming you use plain water boiling point of water is 100 C. if you are using a pressure cap of 12psi that increases to about 111 C. so I would assume that you are boiling over, but you have not said your loosing water.
The symptoms you describe are typical of the engine boiling over or reaching that sort of temperature. I would suggest that you look at the following.
Check and replace the thermostat if required.
Tune the engine.
Ensure the fan belt is correctly tensioned and is in good repair.
Flush the cooling system, this should be done with a high pressure but not a jet washer unit. Ensure that the flow of water is reversed to remove as much crud as possible. However this can knock small partials off the inside of the rad. thus causing leaks.
To ensure that the cooling system does not silt up again I would suggest you use anti-freeze in the future. (if you can purchase it in HK)
Finally I would also have the head checked to se if it has warped. Although the B series engine is a tough unit that can fail occasionally. Maybe you should consider replacing the head gasket.
Cecil Kimber

Even if your radiator is new, the core may be
cheaply made and not cooling well. Consider
getting your radiator re-cored with four instead
of three rows. The stock three-row MGB radiator
is really marginal in hot climates, and 30deg C
is really hot by British standards.

If the temp drops significantly with the heater
on, then this is a good indication that the
radiator itself is marginal.
Ronald

thanks!

i used anti-freeze & the cap is 9 psi, i found that it lost about 1/2 litre coolant(which may due to boiling over).
the engine was overhauled with the radiator flushed at about 1,500 miles ago.
this weekend i will go through everything again including valve tappet gap, spark plug gap, contact breaker gap, timing ..... and hope that the cylinder head is not warped.
ennio wong

Yout thermostat could be sticking closed and therefore you may not be using the radiator. Try taking it out and putting it in a pan with water with a temp gauge. See if it opens and at what temp. New ones are only a few dollars and worth replacing from time to time. I'd run a 160 or summer temp thermostat.

Also, you could have an air bubble in your system that did not come out when the system was flushed. Remember that the heater should be on when you flush to get all the air out.
Steven O. Vandal

I live in the tropics with temperatures regularily up to 35 c. My mgb roadster usually runs at 90 degrees, it will increase in heavy traffic. The car is fitted with what we call a tropical radiator, ie fatter than usual.
guess it all boils down to the cars not having been designed for these climates
Rgds
Mark
Mark Taxis

This thread was discussed between 26/05/2002 and 30/05/2002

MG MGB Technical index

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