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MG MGA - Sleeved Thermostat

I have definitely joined the ranks of the Dominic Clancy cold running car brigade.

Until a couple of months ago I was running a sleeved 74 degree thermostat that had been holding the cockpit gauge at about 175 to 180 degrees in these British climes. However, the stat was beginning to look on its last legs as the temperature was edging up to 190, so I replaced it with an ordinary 74 degree stat from Bob West.

The car has since run at 160 and never goes a degree higher. It has been bit cold here in the last week (about plus 2 but still nothing like the outbacks of Canada!) and I found that the car took ages to get up to temperature and needed more choke for longer than I am accustomed (about 1/2 to 3/4 mile).

This weekend I put in an 82 degree stat. All that has done is raise the running temperature to 162 degrees maximum, not even a needle's width higher than the stat 8 degrees lower.

Can someone explain what is going on?

Puzzled

Steve
Steve Gyles

Steve
I am no expert on Thermostats but changing a thermostat should only effect the opening temperature; and not make much difference to the running temperature if it is working correctly. I can only surmise that the old stat was somehow restricting the water flow and allowing the block to hold a higher temp perhaps not opening fully ?,
I am not sure what themostat is in my Mk 2 Coupe but mine runs at 160 all day unless I am in very slow traffic when it rises to 190 max. As it seems to work OK I am tempted to leave well alone
Paul
P D Camp

Thanks Paul. You make me feel less lonely! I guess I had become accustomed to the higher temperature from the sleeved thermostat.

What still puzzles me is that others appear to use these thermostats to reduce the temperature, not increase it - or have I been misunderstanding previous threads on the topic?

Steve
Steve Gyles

That's my understanding as well Steve.

With the thermostat closed, some coolant is allowed to flow directly back into the block through the bypass port without going through the radiator, thereby allowing the engine to reach operating temperature more quickly. When the thermostat opens, the sleeve raises up and blocks the bypass port forcing all the coolant to circulate through the radiator.

I'm at a loss to explain your siuation.
Andy Bounsall

Steve's experience reflects mine 100%. A 10C difference in thermostat made absouely no discernable difference to operaing temp. A sleeve made the temp drop by a significant amount. I have a standard radiator core.

I have now fitted a radiator blind, ( a bit more elegant than the slab of cardboard I used to use) which I must use on cold days to get above even 50C, otherwise I have to run with permanent choke. When using this, I can close off up to 80% of the rad area before I see a difference in operating temp. When the temp rises, it comes fast. I'm still getting used to the blind and its foibles...

Steve, Bob offered me one of these back in August which was still in the packing - it was under the table in the shed that faces you as you drive in from the road, back right hand room, table in the left hand corner as you come in from the door. I would expect that it remains unsold... It was complete NOS, and if I hadn't already done all the mount fabrication on the Magnette blind (I got it from Gordon in Canada) so that it can hardly be seen, I would have taken it immediately.
dominic clancy

This thread was discussed between 24/11/2008 and 25/11/2008

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