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MG MGB Technical - Early 3 main bearing MGB engine High Water temper

During past few years I have checked my temp gauge, replaced the pump, cleaned the radiator, installed a latter multi-blade cooling fan.
In summer, not just this one, if I raise my cruising speed over 70 miles an hour my water temperature slowly, but definitely starts climbing. It will go beyond 100 degrees C. if I do not cool it. Has anyone got a sensible solution.


Frank
F Navest

100ºC is not unreasonable. If it's not boiling over, it's not overheating. What temperature thermostat, what pressure radiator cap, and what proportion antifreeze/water are you using?
Rob Edwards

Frank,

Has somebody put radiator sealer in your water system in the past? Most of the pipes might be full of the stuff, this was the case with my '64 MGB. On my car the water came out orange. A test would be is the heater working? If not it might be blocked and water flow might be restricted.

Is your ignition timing right? This is a common cause of hot running.

Do you have an oil cooler fitted? They were optional on early MGBs and are definitely a good idea. I run a bigger than usual oil cooler which I prefer the thought of on a 3 bearining engine.

Are you running unleaded petrol? Modern fuel burns hotter and can put a strain on an old cooling system. Just look at the size of the radiator on a modern car! The solution is to have your radiator re-cored with a bigger core. I have not done this yet but I am planning to, last time I had radiator work done it improved the running temperature by allowing the car to stand in traffic without too many problems.

My car runs 190 Farenheit (it's not got a Centigrade guage!), since 212F is boiling this equates to about 90 Centigrade I think, but I haven't done the conversion. I run a 286 camshaft with richer carb needles and everything else standard.

John.
John Prewer

100C is pretty high, but I'd agree with the 'if it's not steaming or losing coolant it isn't overheating' statement.

Overall it can be a case of the engine producing more than it should, or the cooling system not being able to get rid of as much as it should. But first you need to confirm the gauge is accurate with another measuring instrument, it is possible it is reading high, *and* the thermostat has a problem, the two cancelling each other out until you start using more performance.

As has been said timing can be a big factor in the first case, especially the centrifugal and vacuum advance mechanisms. You need to plot your curves and compare them with the originals. If you are not getting enough additional advance you will run hotter, even 2 or 3 degrees is enough to make a difference on the gauge I have found.

Not sure of the details but I have seen several times that the incorrect water pump can cause problems - although it physically fits it does not shift as much coolant as it should.

Ambient also is a factor, and at the moment with the warm weather cars of our era *will* run hotter on the temp gauge. Modern cars have the temp gauge controlled by the engine ECU, so it doesn't show 'normal' variations, it only starts reading high when you really need to stop and investigate.
Paul Hunt 2

Hi Folks:

MGA/MGB 3 main blocks have no water jacket between #2 & #3 cylinders. This configuration was changed in the 5 main B series engines. Note, with over boring 0.040 and up, expect higher operating temperatures.

Thanks: Rich B
Rich B

my car runs @ just under 160F on the open road.

in traffic it climbs steadily to 190F but still boils in the heaviest traffic.

obviously the cooling system must be in a decent condition? its recently been flushed and i am running the better earlier radiator that uses the full rad, with opposing outlet/inlet.

can anything be done to improve the cooling?
d buck

Frank-
The fact that the problem develops at higher engine speeds is the clue. Check the feed hose that goes from the bottom of your radiator to the coolant pump by giving it a good squeeze. If it compresses, then chances are that at higher engine speeds it is collapsing and impeding coolant flow.

d-
A radiator shroud from Moss Motors and adding the later seven-bladed plastic fan will make a big difference in heavy downtown traffic on a hot day. The earlier cast iron-bodied long-nose coolant pump has a much better cast impeller design than the later aluminum-bodied short-nose coolant pump with its stamped sheet metal impeller. If that's not good enough, replacing the core with an aluminum multi-row core should do it.
Steve S.

steve - i will take your advice and order those parts tonight.

thanks!
d buck

I have a 1970 GT that is also showing overheating on the gauge. I have replaced the radiator, water pump, all of the hoses, the gauge (two time - I even went to an aftermarket that has the actual temp), the sending unit, the T-stat - two times(165F), I have checked the compression (all cyl at 120 lbs). The gauge is showing that it is running at 210F. Checking the water temp at the radiator filler it never exceeds 170F and I am not pushing any fluid out. I am at a loss.
M Lang

If the temperature at the radiator filler never rises above 170F then that is the temperature of the coolant in the engine regardless of what the gauge(s) says ... *unless* possibly the stat isn't fully opening. Test it without a stat in at all and if the radiator filler still shows 170 or less then that is what it is. This is an electric temp gauge, right? The gauge is only half the equation, have you tried a different sender? The electric temp gauge and fuel gauge will also read high if the voltage stabiliser is not doing what it should. This is supposed to switch 12v on and off about once per second (after a 2 or 3 second warming-up period after first switching on) to give an average voltage of about 10v. If you measure 12v both sides of the voltage stabiliser (green wire one side, light-green/green the other) several seconds after switching on it is faulty. It needs a good ground from its fixing screw to work properly.
Paul Hunt 2

Thanks for your input Paul. I will check it out.
M Lang

This thread was discussed between 23/07/2006 and 26/07/2006

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