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MG MGA - Head Temp vs coolant temp

My head seems to get real hot on my car, but the coolant seems to be about right. I don't know the exact temp of the coolant because when I bought the car, the PO said, "the temp gauge always stays on the cool side ". Yep, after the purchase I found it's that way no matter if the car is running or not, because the temp gauge is stuck in the same spot.
I can't touch the head on the spark plug side because it is so hot after a few minutes driving.
Does that seem normal? If I were to get a meter/sensor to read the temp of the head, does anyone know what temperature it should be when warmed up?
Cleve Crews

Cleve,
The head will feel extremely hot to the touch. Even 150°F will burn or scald you, so its not really a very good indicator since it will burn you at normal engine temperature anyway. I would get a new or good used dual gauge. The last time I looked, the major British car parts suppliers in NA have them for a reasonable price. You can have them repaired also, but I don't know how the price compares to new. Its really nothing to fool with, you need to know the engine temperature at all times.

Ralph
L Poupard

Cleve,
If you really want a head temp measurement buy a non-contact IR gage or use a thermocouple on the surface of the head I don't know what the temperature should be, but think it ought to be around 180-200 F.
Cheers,
Gerry
G T Foster

I have had water temp gauges in my cars before and noticed that at shutdown of the engine, the water temperature came up about 15F every time. I would assume that the head temp would be this temperature.
Mike Parker

Yep I think Mike is correct that when the engine is stopped the water temp rises significantly. Also if you tried to remove the pressure cap when the engine stops the water would immediately boil and is therefore really above 212 degreesF. Thus the temperature of the head/block must be higher than the running temperature of the water

The surface of the head as stated above is always probably too hot to touch so the only sure way of knowing you engine is "safe" is to get a good working water temp gauge and put you faith in that. I think it is a far simpilar job to fit a new gauge than try and speculate what may or may not be.
Robert (Bob) Midget Turbo

Cleve, test your gauge in a pot of boiling water!
Art Pearse

In a water cooled engine everything up top will be about the same temperature as the coolant. If the thermostat holds coolant temperature at 190dF, then outside of the head, thermostat cover, and top radiator hose will all be within a few degrees of same temperature.

Internal head temperature will be higher, in the area of combustion chamber and particularly near the exhaust valve seat. This higher internal temperature is what drives heat outward into the water jacket while running. When the engine is shut off and coolant (almost) stops circulating, the internal heat migrates outward, cooling the combustion chamber while it heats the coolant fluid. This is when you see the temperature rise as much as 15dF on the temperature gauge within a few minutes after shut down.

Indeed you can burn your fingers on the cylinder head or thermostat cover when it is running around 190dF. The radiator hose may feel not quite so hot to the touch, because the rubber hose is a bit better thermal insulator than the metal parts, and it transfers heat to your hand slower.
Barney Gaylord

Everyone,
These are great answers. I haven't had the car out on the road since I brought it home for fear of damaging the engine after noticing the gauge never moved. I took out the stat this morning and checked it for function, and it was fine.
The A is behind some other cars in the back of the garage, so I'll take it out and test it ASAP and let you guys know what the temp is with a new gauge/sensor.
Thanks!
C
Cleve Crews

http://www.raytek.com/Raytek/en-r0/ProductsAndAccessories/PortableThermometers/PortableThermometersSeries/MiniTemp-AutomotiveHandheld/Default.htm
These are great to check temps.
R J Brown

This thread was discussed between 16/10/2011 and 17/10/2011

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