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MG MGB Technical - Radiator/hot condundrum

Hi all, I am still having problems with engine temp - too hot. The issue is this: went for a drive, (great weather for mgb driving)but engine becomes too hot according to the gauge. Got home and decided to check coolant etc. All pipes from rad are very hot as is the rad itself - also that which goes to the expansion tank (late model rad). The odd thing is that the coolant in the expansion tank is cold (I know because I put my finger in it!) There was a bit of pressure resistance when I screwed the cap off but no heat at all. The coolant level in the expansion tank is just above half full.

So pipes very hot,the tube from the rad to expansion tank does not appear to blocked by anything.

So what an earth could be the problem? Possible air bubble somewhere?
Moss

DO NOT believe the gauge, until you have tested and verified the calibration. Measure temp at the thermostst housing, preferably with a contact thermometer, or a verified infrared unit that you actually know how to use. Once you know what YOUR gauge says relative to reality, you can use it for indication of changes - but they do lie!

If water is not blowing out the expansion tank, then the engine is not overheating, if we suppose that there IS water in it. If the expansion tank is cold, water is not being blown out.

The rad is meant to be hot. 192F stat are standard. 50/50 antifreeze and a 15lb cap mean the engine can operate at beyond 250F without loosing water.

FRM
FR Millmore

Hi FR, my infrared thermometer -is verified- says thermostat housing at 3 inch distance is between 199F and 202F - 3 readings over 90 seconds. The radiator front, bumper side is 184F and engine side 200F. Stationary, of course. The gauge just below red.

I recently changed the coolant - 65 % coolant 35% water. For warm weather the mixture is possibly to rich?(just thought of that). The problem could be that the heat cannot escape from the fluid due to the mixture...

/Moss
Moss

Moss-
200F is OK but a bit high, if the weather is not hot. Within range for a 192 stat, high for a 180. MGB fan switches are horrible devices, wildly inaccurate and variable in both settings and hysteresis. Somewhere
I have the results of several days measuring all this.
For perspective, my Mazdas have 192 stats, the temps at the engine out are 192-200, and the fans only come on at 210 - every time!. But they rarely DO come on!

The gauge is high for that temp, so subtract a quarter scale. Car temp gauges are "relative indicators" not "real temps". "N" should be 180 or even up to 192.

65/35 is far too rich. Assuming "coolant" means straight gycol. Read the table usually printed on the bottle.
I run 50/50, good for -37F and over 250F at 15 psi cap.
And cheaper and better cooling.

Critical thing for rads is very pronounced difference between top hoses (hot in), and bottom hoses (cool out). I have not recorded numbers, but c 50 F at minimum I think - obvious by touch.

Since you have an IR, scan the rad, up and down and across in a grid. The temp should have a fairly uniform drop top to bottom. Any cool spots are clogged tubes. No cool spots and no/small temp differential is no circulation - bad pump, hoses, or stat.

FRM
FR Millmore

I would have to agree that your problem is most likely based on the fact that you have too much antifreeze in your cooling system. I think that a 35% mixture of antifreeze, to a 65% of distilled water, will solve your overheating problem. Your present mixture just can't dissipate the heat from your engine through the radiator fast enough. RAY
rjm RAY

Thanks for the advice chaps. Will change the coolant to a thinner mixture. The rad does not look in very good condition, not the original but not new either. However, not leaking. Forgot to mention that the fan is on the water pump pulley so fan starts to rotate as soon as the engine is running. The engine has been de-smogged. I'll also do the check on the rad - top and bottom temperatures.

I'm also getting alot of 'run-on'.
Last time after a longish trip so engine was at a good temp it ran for about 4 seconds....must get it sorted out - the engine does not like it and nor do I,but that is another story. I'm using 95 octane (not optimal, I know) and the idle mixture is as rich as possible. I am supposed to have a 'lead free' valves.

/Moss

Moss

If that is 95 RON it should be fine for a US spec asthmatic. They run fine here on 87 pump, which is the average of RON and MON.

If you have a 77 with the forward set rad and a pump mounted mechanical fan, you are beating a dead horse with wet spaghetti. No shroud, a foot to the rad = no air through rad. And it will sooner or later remove a hand or worse - scrap the propellor. Get an electric one with a thermo switch. Wire it with a relay.

Hot engine plus high idle always = run-on. = Same story!

FRM
FR Millmore

The engine is a 846F recon so not US spec anymore. With a 32 36 dgev weber down-draft. Yes, the electric fan - a Kenlow, is on my list. Idle at 750 rpm. In the winter I'm going over to HIF4 carbs. Already seen a set with my name on it...
/Moss
Moss

Moss, don't overlook other reasons for overheating;
1. Lean mixture,
2. running too advanced ignition
Both of these will also exaggerate your running on.
3. binding brakes,
4. low oil
5 clogged rad matrix
6. tight engine
Al
Allan Reeling

Also too retarded ignition. Other than too much AF relative to the water though, I still haven't read anything that convinces me you have a problem at all. Sounds like it's running within spec.
Rob Edwards

This thread was discussed between 05/07/2012 and 07/07/2012

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