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MG MGB Technical - Thermostat reliability

Mine seems to have packed up - a first for me - is this common ?
R Walker

Not unusual. I've had defective ones right out of the box, that stayed open all of the time. RAY
rjm RAY

Never had one fail in 40 years, but of course like anything they can. The biggest problem these days is as RAY says - defective new parts.
PaulH Solihull

They do fail sometimes. I put one on the MGB in 1988.
Stan Best

I had two fail within one year. I live in Florida where I don't really need to use the heater and put in a blanking sleeve.
JCH Hibbard

Well easy enough to change even on the V8. They are generally reliable - US made ?

I was surprised to read of the blanking plate - The thermostat must be pretty redundant in Florida (unless you drive to Canada) but shouldn't the space be left empty ? - so that the water circulates through the rad ?
R Walker

Its common practice to use the blanking sleeve and a thermostat on a street engine. The sleeve causes all the flow to go through the thermostat and radiator. Its best if you do this to enlarge the small bleeder hole in the thermostat to 1/4" and (if it has one) take the little toggle thing out.
Denis
Denis4

Aren't there two different things that are used? I'm thinking the blanking sleeve blocked the hole in the head that otherwise allowed some circulation through the head regardless of what the newer style t-stat is doing. I also thought the original style t-stat blocked this hole during warm up.

Then, I thought there is a blanking plate that reduces the size of the big hole between the head and radiator at the t-stat location.

Walker, not all of the flow is blocked with a blanking plate, so the coolant still goes to the radiator.

Charley
C R Huff

The blanking sleeve restricts the amount of circulation from head direct to block i.e. bypassing the radiator which can cause overheating, but is perhaps more of an issue with As and very early MGBs with a large bypass port. What is more important with MGBs is a restrictor plate which limits coolant flow to that of a fully open thermostat, without that you can get turbulence and local recirculation in the cooling circuit which gives rise to localised hot-spots. Allegedly. All in all it seems easier to use a stat as they came out of the factory and be done with it, they don't overheat in desert states as the factory issued them.
PaulH Solihull

Hi All,
For what it's worth, I had an Austin, back in the 60's, with a B series engine. Every time the ambient temperature went above 90 deg F the bellows style thermostat blew. The bellows split. After several bellows type 'stats I used a generic "Waxstat" and never had any more troubles.

Herb
Herb Adler

I have recommended using a blanking sleeve for many years before Moss decided to retro engineer some of their current T-stats to act like the original Smiths that came with MGAs and early MGBs. You can read what I did and said here: http://www.britishcarforum.com/bobmuenchausen/12299.html .

However, as I stated there, the main thing I have seen happen from using the blanking sleeve is simply that when pulling a long (4-6 mile) 6% grade such as we often have here in the Western USA, it takes noticeably longer for the coolant to begin its rise in temp from the strain on the engine. I could say that it has also kept the engine temp in line in long stops in 100F+ summers, and generally seemed to buy some "headroom" for the cooling system which is never a bad thing and which may have a salutatory effect on its performance as it dirty's up.

What has probably been of greater importance for most folks I have talked to is simply establishing what the letter markings on the temp gauge mean in actual degrees (as discussed on that web page above also). A lot of folks freak out as they see that needle rise and have no good idea what it is actually telling them. Taking some actual operating temps and corresponding them to the markings on the gauge can make a lot of owners less nervous.
Robert Muenchausen

This thread was discussed between 12/10/2010 and 11/11/2010

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