MGB-GT 1972 GBT overheating

[strategiclynk]

If idle, in 15mins it's on the "H"
Please help

 

[bobhustead]

Are you new to the car or is the condition new to the car? Assuming you are staying full of coolant, common problems include a bad thermostat, bad radiator cap, loose fan belt, dirty radiator core, poor air circulation thru the radiator fins. Does it cool properly at speed?
Bob

 

[strategiclynk]

Hi Bob it does cool properly on the highway
Not new to car, radiator is new, the thermostat/and switch is new and the water pump is new
The fan is constantly spinning, is that normal

 

[DrEntropy]

What year is this car? Electric fan?

 

[DrEntropy]

What brand water pump did it get? If it was one with a pressed steel impeller, it cavitates. Only the "Gold Seal" and "Heritage" pumps work as they should. We're in the Tampa Bay area and our MGB can sit in July traffic all day with no issue. Aluminum radiator, Gold Seal pump, electric "pusher" fan and 72°C (160°F) 'stat.

 

[strategiclynk]

DrEntropy: The car is 1972, it's the mechanical fan not electric.
The water pump I got from Moss.

 

[DrEntropy]

Hi Bob it does cool properly on the highway
Not new to car, radiator is new, the thermostat/and switch is new and the water pump is new
The fan is constantly spinning, is that normal

So it seems air moving through the rad while under way keeps the temp down, indicating the t'stat and radiator are doing their job. At a stop, it seems the pump/fan are inefficient. The fan is mechanically connected to the pump and, yes, should be spinning constantly while the engine is running. Belt tension is a variable, as is which pump you got from the supplier. And you stated something about a "switch"? What switch is that? Not aware of any switch before 1977 models.

Dealing with sixty year old British cooling systems never designed to operate here in our climate/conditions, means every component needs to be in top shape. Again asking what brand water pump was fitted. If it is one with a stamped steel impeller, not a cast metal one, it will be inefficient.

In case you haven't seen this PDF from Moss Motors: The reason I question what pump was fitted. The "Gold Seal" pumps are the only ones we've fitted to any MGB coming into our shop with pump issues, for years. The stamped steel impeller ones are junk-out-of-the-box, AFAIC.

Just trying to narrow down possible causes, another question is how the fan is mounted. The '72 version should be metal with six blades and it can be mounted backwards... can you post a photo of the front of the engine showing the fan and pump?

 

[Joe Reed]

What DrEntropy is getting at is that the fan blades are not flat....they are curved. The fan can be installed backwards and still look 'kinda" correct if you don't look close. As the fan turns the curve of the blades sorts of scoops the air from the radiator towards the engine. Think about how you curve your hand if you want to scoop some water. If the blade is backwards the curve faces the other way.....sort of like if you tried to scoop water with the back of your hand.
The difference isn't usually noticeable while the car is moving at any speed since the volume of incoming air forced through the radiator is far greater that what the fan can move. At idle, or even very low speeds, the inefficiency of the backwards fan becomes apparent.

 

[JPSmit]

The other thing I might add is whether the rad itself is clogged or bocked. You might be able to tell fif you had a laser thermometer - maybe <maybe> even judiciouly touching the rad at different palces when hot to see if the heat is uniform.

 

[DrEntropy]

JP. the initial description was the radiator and thermostat are "new", so I've assumed that to be so. That it goes to normal temps when driving would indicate the block is clear enough, so not much left except poor belt tension, fan on backwards and/or cheesy pump.

I'd like to think we'll get a follow-up post from Strategiclynk.

 

[JPSmit]

JP. the initial description was the radiator and thermostat are "new", so I've assumed that to be so. That it goes to normal temps when driving would indicate the block is clear enough, so not much left except poor belt tension, fan on backwards and/or cheesy pump.

I'd like to think we'll get a follow-up post from Strategiclynk.

doh! missed that