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MG MGA - Moss Sleeved Thermostat

Back in 2004 when I put together my new cooling system as part of my restoration I don't remember this part being offered by Moss:
http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=47024

As I was about to try adding a sleeve to my setup to aid in cooling (we're taking it to Key West in April) I'm thinking maybe this is a better solution. It's a 160 deg unit, and with the sleeve as an integral part it would seem to be "ideal".

Has anyone installed this type or have any suggestions about using it?

- Ken
Ken Doris

Ken- I installed the blanking sleeve only in my car and did not notice a difference. Don't think that by adding a thermostat to what is basically a blanking sleeve would make any difference either. You could try it and let the rest of us know, and whats the worst that could happen, get stuck in the Key's? Good luck and have fun, Gary
gary starr

Personally I'd stick to the separate sleeve and thermostat. If that thermostat failes on you out on the road, you wont be able to pick up a new one at NAPA, and you don't really want to run without a blanking sleeve in there while you're waiting for a new part.
Mark

Gary - you definitely have a point. "Sorry boss, I can't come in to work today, I'm stuck down here in the Florida Keys" does sound pretty good.

Mark - seems like you feel running without a sleeve is a bad idea. Are they really that useful? I ran this past summer with just a thermostat, and although I'm looking for better cooling, I didn't have any major problems, running only once in the 220 and up range on a really hot day.

- Ken
Ken Doris

Ken,

There is a bypass port in the head. It's for bypassing the radiator and keeping warm water in the engine during the warm-up period. The original thermostats (and the new Moss ones) had a moving sleeve design which blocked off the bypass hole once the engine reached operating temperature. If this hole is open during operating temperature, there will always be some hot coolant that is recirculating itno the engine without going to the radiator to cool off. This can affect the overall running temp of your engine. If you use a regular thermostat you have to also use the blanking sleeve to get the most efficiency out of your cooling system.
Mark

OK Mark - I now understand the bypass hole, with the help of Barney's website and its great pictures. Reading that section however, it seems that by combing the blanking sleeve and a normal thermostat the result is a very long warm up since the bypass hole is always covered. Barney recommends drilling a hole in the outer flange of the thermostat to help with that problem. Am I understanding this correctly - that with the sleeve comes a much longer warm up?
- Ken
Ken Doris

How long is a much longer warm up?

I have run both an MGA with the 1950cc mod and an ordinary MGBGT 18GF engine with a combination of the blanking sleeve and a "Balanced Thermostat" (originally marketed by Robertshaw, now marketed by Prestone) for a lot of years and find that summer and winter, warm up takes about 1.5~2 miles. The temp tends to stay well regulated, and my uneducated guess is that the bypass system was a nice engineering exercise but not totally necessary.

I will have to go back out to Barney's site and revisit his comments as I sent him some of these "balanced" t-stats to try out and frankly forget now what he had to say about his findings.
Bob Muenchausen

I see he never received them. But at least he got them from Phil Bates.
Bob Muenchausen

Ken,

I totally agree with Bob's comments. Eliminating the bypass hole doesn't significantly increase warm-up time. Like Barney says, you can drill a larger hole but I didn't find that to be necessary. It's hard enough to keep the car cool (especially here in city traffic), so I'd rather know that my system was running as efficiently as possible.
Mark

OK, seems like it's almost unanimous - I'll order a blanking sleeve, a new 160 thermostat and gasket and use that combo. I'm nervous about using the Moss part I cited at the beginning of this thread as Barney's site has some info on the original version and apparently its use in pressurized systems is suspect.

- Ken
Ken Doris

A 160 F T-stat may be a little low for proper engine performance, but try it. Most BMC B-series engines I have encountered seemed to do well with a 180F or 195F T-stat, but check out Barney's site for his insights on this point. Your need for a low temp T-stat may be due to other reasons.
Bob Muenchausen

With the blanking sleeve and thermostat with a small hole in the flange, warm up is nearly as quick as with the sliding sleeve thermostat. It may be the difference between 3 minutes or 3 minutes 15 seconds to thermostat opening.

The reason for using the small hole in the thermostat flange is to avoid completely blocking off all flow during warm up. If there was no flow it would generate hot spots near the exhaust valves and boil the coolant in the head while the rest if the cooling system is bone cold.

The small amount of coolant which passes through that small hole and through the radiator during warm up also brings a small amount of cold coolant into the engine from the radiator. This only affects the thermostat opening time to the extent that it reduces coolant temperature in the head. With the very low flow rate the head warms up quickly anyway, maybe even quicker than if the bypass port was open. This means the block doesn't warm up so quickly, but the head warms up sooner. It's the head temperature which most affects the quality of running (fuel mixture and fuel ignition) during warm up.

There is also a fixed amount of heat being generated by the engine. The only way the engine as a whole could take longer to warm up is if the radiator dumps more heat during the warm up period. The time when that would happen would be when the small hole in the thermostat is allowing flow through the radiator. That flow is small, and the coolant in the radiator is particularly cool before the thermostat opens, so the heat loss there is also small and has very little effect on the overall warm up time (before the thermostat opens)

It is necessary to have a small amount of flow during warm up to prevent local spot overheating in the head. But that only requires a very small amount of flow. The bypass port is larger and allows much more flow. The net result of gross bypass is to warm up the block at the same time the head is warming up, but warming up the whole engine at once is slower than warming up the head first. With the bypass open it will take longr to warm the head up to operating temperature, and you may need to run longer with partial choke.

The one condition when the bypass port could serve well would be if ambient temperature is so low that the thermostat might never open, and the engine may cool well enough with no flow at all through the radiator. Then the internal circulation would provide more even temperature through the block and head, which might be good for the block and piston rings and oil temperature. So how cold does it have to be for the thermostat to never open? -20dF maybe? And how many people drive their MGA when it's that cold?
Barney Gaylord

Barney - Thanks for joining the dialog - from what I read in your response, adding the hole to the thermostat flange is a simple, yet very useful modification, in terms of keeping the head from generating hot spots - correct?

And yes, I think the great majority of us don't take our beloved A's out in below zero temps! Although I know that wasn't the case back when I was 23 and the car was a very young 6 :)

- Ken
Ken Doris

Yes, the little hole is enough to prevent boiling hot spots in a cold engine, if you use a blanking sleeve to close the bypass port.

When I was 19 I drove an MGA right through the winter, when temperatures stayed between -20/-10dF for 3 weeks, and salt would not melt ice on the roads. Jolly good fun getting up at 2am to run the engine for 15 minutes so it would start in the morning. For part of that time I had the entire radiator blocked with cardboard. When it finally got into the -10/0dF range I had 1/6 of the core area open for air flow.

When ambient temperature is below 0dF, I think it is important to use the bypass port for general circulation at normal engine operating temperature (if it ever gets up that high).
Barney Gaylord

This thread was discussed between 30/01/2006 and 01/02/2006

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