MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Engine running too cool

It was a cool morning Sunday with the temp outside around 49 degrees. I decided to take advantage of the morning and lightly traveled roads with a little jaunt in my 74.5 MGB. I noticed that the temp gauge never really got moving except when at a red light and then only edged up a bit, never even approached the middle of the gauge. Because it never got warm the car ran a bit poorly at low speeds and wanted to stall a few times. I have a PO Weber carb conversion and manual choke. I am running a 160 degree thermostat which is only about 5 months old. I had replaced the 190 degree one when I had the head rebuilt. Even with the 190 thermostat the engine really never heated up much when moving (except when the ambient temperature was in the nineties). The radiator is new. Other than blanking off part of the radiator in the cooler weather will a new 190 degree thermostat help the engine heat up?
John

Have you measured the temperature of the water in the radiator? The gauges can read low, so the real test is to pop a thermometer in there. It should be around the 180* mark after a run.
Steve Postins

John - I suspect that your temp gauge is lying to you. Take Steve's suggestion and read the actual water temp in the radiator after running the car for 30 minutes or so and see where it is reading. If it is anywhere in the vacinity of 180°, then you may want to conside a new temperature sensor. I would also highley recommend going back to the 190° thermostat (or at the very least 180°) as the engine is happiest at those temperatures. The lower thermostat temperature is not going to keep the engine from overheating or even hold the temperature at 160° when the car is running, it ONLY set the lower temperature that the engine will operate at and 160° is not a temperature that it likes to run well at. Good luck - Dave
David DuBois

Thanks for the replies. The temp sender is new and gives the same reading as the older one (I had thought the older one may have been defective and that's why I replaced it). Perhaps the it's temp gauge that's not showing the correct reading, I will check it as suggested. Also will go back to the 190 thermostat.
John M

The instrument voltage stabiliser may be bad. This will also cause the fuel gauge to read low. (low or high - same as temp gauge) The engine ground may be bad, causing the engine to be above true ground; this will make the gauge read low, and also cause undercharging, since the Alt/reg uses the engine ground as a reference also. Check from Batt- to engine with a voltmeter, with engine running at 2500 and all electrical loads (lights, heater blower, etc.) ON. Reading should be less than 0.5V, preferably no more than 0.2V.
FRM
FR Millmore

If the Voltage stabilizer is bad, it will also affect the operation of the fuel gauge, so if that is not happening you can rule out the stabilizer. There are two different temperature senders used for the electrical temp gauges in the MGBs. You might check if you have the correct on installed. Fletcher is also correct about the engine ground having a large effect on the temperature gauge, definitely worth a check. Good luck - Dave
David DuBois

You can check it very accurately using an infared sensor. You might be able to rent one somep[ace. I bought one for 40 bucks at a local car parts store to check tire temp on my motor home.

Chuck
CW Strong

John,

As a 74.5 your car will have had an engine driven fan when new. If your gauge is correct and you still have the original fan fitted you could try removing it and fitting an electric fan. This would improve warm up.

David
David Witham

An electric driven fan will make very little difference to warmup. It is the thermostat that controls how quickly an engine warms, until the stat gets up to temp and opens there is no hot coolant running through the rad for the engine driven fan to cool. An electric fan is more about reducing lost energy and noise, plus improved cooling at low road speeds i.e. when slogging up a hill. With a correct thermostat and temp gauge indication it should always be around N, even in winter - UK winters that is. Bad connections in the temp gauge circuit will also reduce current and hence gauge reading. If the engine ground strap is bad that will be most noticable as slow cranking and hot accelerator, choke and heater cables and can easily be checked by messuring the voltage difference wbetwen an engine ground and a body ground. Even when cranking this should be only 0.5v or lower. Replacement temp sensers have also been found to be bad. Measure the voltage at the sender when the engine is up to temp and you would expect it to be showing around N, this should be about the same voltage reading as when showing half a tank of petrol. Bear in mind that the 'stabiliser' actually switches 12v on and off about once per second, if you use a digital instrument it may not 'settle', you will be better off with an analogue.
Paul Hunt 2

This thread was discussed between 26/09/2005 and 28/09/2005

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.