Morris Minor Owners Club

Why do some people use different temperature thermostats in Winter and summer? I can see that the 88 degree one would result in the heater being warmer at the start of a journey in Winter but once everything is up to temp. ie.thermostat open,I would have thought that it was irrelevant which was fitted. Does the engine never get above 88 degrees in Winter and the thermostat remain closed for long periods?. If the engine runs hotter than 88 degrees in Summer it would seem logical to use the higher temp. thermostat all year round. I'm going to change the thermostat and I'm wondering which one to use.

I personally would go with an 82c one as mine are rarely out in winter

In winter if you want a decent working heater -use the 88. It's not a switch - open/closed - it will modulate around that point , probably more closed than open most of the time - and indeed yes in winter, driven slowly/in traffic it may well struggle to get to 88. In summer we hope the weather will be warm and sunny -so -to give a bit of a 'buffer' in case of flogging up a hill on a hot day, a 74 stat allows the engine a good running temperature and that safety margin for periods of 'hard work' . but it's up to you! Why are you changing it - just curiosity, or do you think there is a problem? beware the frozen studs/thermostat cover...... plenty of release oil (which is not WD40) - and run a drill bit through the cover fixing holes to open them up very slightly, and grease the studs well when refitting.

Thanks for the replies - it's great to have such a wealth of knowledge at the press of a keyboard! I am probably being thick but I can't see how a 74 thermostat would affect the running temperature of the engine in summer - surely once the temp. exceeds 74c (which will be most of the time in summer) the thermostat will be inactive ie.fully open. I'm not trying to be a smart a---,- just trying to understand what's going on.

PS. Thanks for the advice re. removal and fitting. Just replacing as a precaution because I've only just got the car so I've no idea what's in there!

To give a little perspective: I usually run an 88 degC thermostat in winter and a 72 degC one in summer, but so far this year I've left the 88 degC in. I also remove the fan blades in winter, and have yet to put them back on.

The temperature gauge (a mechanical capillary Smiths type) consistently read 65-75 degC in winter, and now is inching into the 80-90 degC range. After parking and shutting the engine off, the gauge regularly rises to touch 95-100 degC, just for a moment, before beginning to cool. When it starts getting nearer to summer, I'll put the fan back on, but I intend to try leaving the 88 degC in as long as I can.

82 is a happy medium

The reason for the 74 is indeed to ensure the engine runs reasonably at / around 74 degrees - but you have that margin during 'hard work' in hot weather for everything to get hotter without boiling . Personally - unless you feel it's running desperately cold with no decent heater - i would be leaving well alone. You'll soon find plenty of things to work on/spend money on without tinkering with a thermostat /snapped studs/stripped threads etc which is probably perfectly good ! They are very reliable. I would just add - you must never run without a thermostat fitted except in competition use - when a 'blanking sleeve' may be fitted instead.

With a nice and clean cooling system I wouldn't go below the 82, which is what I run year round (different weather though).

The reasoning of this is that the Minor's cooling system is big for it's engine so whatever thermostat you fit that's pretty much the temperature the engine is going to run at, even with hard use given the radiator can cope easily with the engine.

Having the engine run too cool will make it a little less efficient and might wear some parts faster. I've ran the 82 degree thermostat in 38 C weather without even a hint of overheating (of the engine, I, on the other hand was cooking).

If your cooling system isn't at 100% (crud in waterways, etc...) then a lower thermostat might be a good idea, or doubling up on the fan blades.

i think the 74 was pretty much the factory standard fit?

When I rebuilt my engine I fitted a new thermostat and housing which came as a kit from ESM. The thermostat is 82 and my heater is extremely good. Also, the holes in the new housing are significantly bigger than the studs, presumably to stop seizure.

My old engine had an 88 degree thermostat and didn't overheat all summer. Even when I took it out in traffic on the hottest day of the year.

bmcecosse wrote:i think the 74 was pretty much the factory standard fit?

Wouldn't know, I wasn't around but since at the time many cars overheated it seems to me they were being overly cautious.

I did a bit of research and, ideally you want your oil temperature to go just above 100 C so any water that may have condensed in it has a chance to evaporate, and 82 degrees still gives a good enough margin I'd think for even the hottest British summer.

Going to Africa or Death Valley? Don't take the Moggy, take something with air conditioning; but if you must then do use the 74.

Ill bear that in mind.......