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MG MGB Technical - overheating MGB

My 1964 mgb roadster is running quite hot. If driven under 60 mph the temp guage reads almost 212 degrees F. I have put a new radiator cao on and changed the thermostat to a 74 degree F. I did put the haeter on and the temp dropped marginally. When driving around 30 to 40 mph the temp came back to arounf 195 degrees F.
Has anybody had a similar experience? Can anyone suggest a cure. The car is fitted with a Kenlow fan which is working.
Any help would be appreciated.
Cheers
Les Howard
Les Howard

Hi Les,
Some ideas to test out

There should be a seal above the radiator to the bonnet, to help with the ram effect of forward motion- is it there?
Is anything blocking airflow?
Check the water level, and look for leaks.
Check the fan belt is tight.
Look for restrictions/flats in the exhaust (maybe the silencer has collapsed inside)
Look for dead flies/mud blocking the passage of air through the radiator.
Check if the ignition timing is retarded.
Check mixture not too lean.
Check hoses havent collapsed internally


Temperature gauge faulty, check it by carefully removing bulb (do not strain the capillary) and drop into very hot water, with a thermometer to compare it with.

radiator core/block silted up, try radflush or similar.
Water pump impeller loose/corroded away, remove and check pump.
Martin Layton

Les - I agree with everything that Martin writes except for "Check the fan belt is tight." If you still have a generator in your MGB, keep the fan belt very looe or you will destroy the rear bushing in the generator - see my article Loosen Your Fan Belt at: http://www.omgtr.ca/technical/tdtf_fan_belt/loosen_up.htm

Putting a lower rated thermostat in will not affect the maximum temperature, as all that it will do is change the minimum temperature the system will run at and will cause the car to be slow warmaing up. In England as here in the Pacific Northwest of the US, it is better to run with a higher temperature thermostat than the lower one.

I think that the first thing I would do is get the car good and hot, then stick a candy thermometer in the radiator fill tube and see what you are reading. Chances are that the temperature gauge may be lying to you. The fact that you are not boiling (steam coming out of the system) while the car is moving or the engine is not stumbling, says that you are not overheating. Keep in mind that with a 50% antifreeze solution and a 7lb radiator cap installed, your boiling temperature is somewhere around 230°F, so you hvve a ways to go. That said, 212°F is not a normal excersion unless the car is being pushed very hard up a long grade on a very hot day. I would add to Martin's list the possibility of a clogged radiator. You may well need to have the radiator recored and the entire cooling system flushed out comercially . Cheers - Dave
David DuBois

Maybe everything has been said, but I would think of it this way:
- Is the gage correct? Most are not
- Is the coolant level good? The sensor is in the head and when the coolant level is low, it does not cover the sensor (reads hot)
- Is the thermostat good? There are lower temp and higher temp sensor - 185 is good
- Are the tubes good? A colapsed tube would do this
- Iis the fan turning?

After there, the follwing ideas help
- You should have a 3 blade fan - there is a 6 blade fan that is better
- You probably don't have a shield. Moss sell them for too much money, but they work
- I recored my radiator - if you do this - I would max it out
- Electric fans help
- Is the water pump any good? The good ones have cast empellers, the junk is bent metal


That is all I can think of
Frank Baker

Hi

Just a tip for any radiator, matt black is the best colour to paint a radiator.
I always lightly spray paint the radiator matt black all over. Theoretically, that is the colour that RADIATES heat the most efficiently. although there is some argument about the insulating effect of the paint. I did some experiments a few years ago on a frogeye sprite and just painting the rad dropped the temp a couple of degrees. A highly polished Rad is the worst at RADIATING heat away, although most heat is CONDUCTED away by the air when running and the colour has no effect on that. If you want to check this, on a sunny calm day find 2 cars in a carpark one silver or white and one black hold your hand close to both but not touching the black one will feel hotter, that's the effect of radiation.

Regards

Simon
S S Tew

Thanks folks for all your comments. I'll get to work on these over the weekend.
Cheers
Les
Les Howard

Shouldn't be anywhere near that temperature in the UK at the moment! Even in ambients of 80+, and with a rally plaque in front of the intake, it only runs about half an 'N's width above N. In the temps we have at the moment it barely reaches N.

Capilliary gauge I assume, so over-reading would be very unusual. Also because use of the heater seemed to reduce the gauge reading it does imply that the system *is* too hot (overheating is only when it is steaming or losing coolant), and not just an over-reading. Whilst turning the heat control from fully off to fully on will probably cause a rediction in gauge reading on all cars, this is because of the lump of cold water that has been injected into the system. In normal circumstances the system should soon restabilise and the gauge rise to its previous reading. Incorrect reading aside higher than normal temps can only be caused by the engine producing too much heat, or the cooling system not being able to get rid of as much as it should.

The former can be caused by incorrect timing and/or carburation, so these should be checked carefully.

The latter can be caused by sludge in the radiator or block, or corrosion of the pump vanes reducing its effectiveness. Also if the thermostat isn't fully opening but I note you have replaced that. The rad can be checked by feeling for any cooler spots across its surface. If you haven't already done it then repeated reverse and forward flushing of the heater core, block and radiator with a hose until it runs clear in both directions.

Check the Kenlowe is working properly i.e. the air-flow is from front to back and not the other way round, and the blades are fitted the right way round. Plastic blades usually have a 'wing' profile that is a blunter leading edge and a thinner trailing edge, and they are less effective the wrong way round.
Paul Hunt 2

You may want to install a recover system if you don't already have one. I just replaced the overflow tube with something more flexible (the one on the car was very stiff plastic - don't know if it was original) and have the other end at the bottom of a 1/2 full overflow bottle from a Triumph Spitfire (yes, I know....). I filled the radiator as much as I could and put on the cap (oh, with a new cap you get a rubber seal that you need to use). As the engine heats up, the coolant is pushed out the tube into the overflow bottle (instead of onto the ground). As the engine cools, the coolant is sucked back into the radiator. The closed system and installing a shroud made a world of difference.
Bill Barge

Les-
Beware of cheap radiator hoses. Due to poor wall strength, they can collapse at high pump speeds and restrict the coolant flow to the coolant pump, resulting in overheating. To test the hose, reach down to the hose that supplies the coolant pump and give it a good squeeze. It should be very difficult to compress. At highway speed it is primarily air pressure that forces air through the radiator matrix, not the fan. Air pressure tends to take the path of least resistance, moving through any open spaces in and around the radiator-mounting diaphragm rather than through the radiator matrix. Therefore, if you want the cooling system to function to maximum effect, be sure that all of the spaces around and above it are well sealed. Do not seal the circular apertures in the radiator diaphragm as they are intended to admit needed cooling air into the engine compartment.
Steve S.

This thread was discussed between 25/07/2007 and 30/07/2007

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