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Cooling System Thermostat


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I am inching forward on my 73 tii that sat for 20yrs and have a cooling system question.  FYI - I searched this forum for "thermostat", got 900+ matches and none on the first few pages were focused on the subject (but all did mention it.  Is there a way to search by subject line only?


I drained the coolant and it looked almost new with not much in the way of crud/particles.  I believe the radiator is original.  I pulled the thermostat and have attached pics.  It literally looks brand new.


Is the condition of the thermostat a good indicator of the condition of cooling passages inside the engine/water pump/heater core?   











'71 MGB - sold   '74 2002 - sold

'89 XR4Ti - sold  '94 Miata R Package - sold

'73 tii - restoration project - sold

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Obviously, the thermostat may be much newer than the engine block, but, having said that, assuming you drained the coolant from the block (ala the drain plug on the passenger side of the block below #3/#4 exhaust ports) you will probably be fine.

Fill the system with BMW coolant (smurf-juice) and see how the car's temp performs. This will probably be as good an indicator as any.

Good luck.

Bob Napier

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One of your thermostat pictures shows a 1992 manufacture date so it's a lot newer than the car; however just to make sure, I'd suspend the 'stat in a pan of water on your stove (tie it to a string so it doesn't touch the pan's sides and is surrounded by water).  Put a themometer in the water and observe the 'stat's opening as the water warms.  At the designated temperature (that'll be stamped on the side of the 'stat that you didn't photograph) the 'stat should be fully open--and the temperature is in Celsius.  Might save you some hassle of having to drain the system again if the thermostat proves to be balky or broken.


I presume you're carefully inspecting all the cooling system hoses (including the heater hoses and that little bitty one that goes between the heater valve and the heater core) and replacing any that are cracked (esp around the hose clamps) or bulged. 




'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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Thanks guys and here are my comments/answers.


Marshall - that's what I was most curious about.

Bob - I forgot about that drain plug and will do it tonight.  Thanks for the reminder!!!!

There is no temp stamped on the tstat just that number "1" but am planning to test it to see where it opens.

New hoses will go all around.

My plan is to use the NAPA Any Engine coolant I have for the moment and until I get it running for a full engine coolant system flush to get as much crud out as possible.

New radiator before the car goes on the road.  new 2002, recore mine or 320 rad - not sure but I know there are posts about the options.

Thanks and free beers when you come to RI.



'71 MGB - sold   '74 2002 - sold

'89 XR4Ti - sold  '94 Miata R Package - sold

'73 tii - restoration project - sold

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Yup, boil it. And watch it open.  It should start to open before the water reaches much of a boil, and open smoothly.


Then turn off the heat, and watch it cool (takes a while) 


It should close smoothly.


Best indicator I've ever found...


but it didn't catch the leaky French one I bought new.  That leaked.  Did I mention, it didn't hold water?



"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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