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Water Temperature K series


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I picked up from your profile that you have a 1.8 K Series. Most people switch to an 82 degree thermostat. The engine tends to run then around 84-85 degrees (in my experience). 70-80 doesn't really make any sense. If you do change thermostat, make sure you drill a small 2mm hole in the outer flange at the point which will be at the top when installed (there's lots of info on here about this). This helps airlocks to escape and is usually enough to make the otherwise nightmarish the job of refilling the coolant a lot easier. It also allows a little bit of flow when the thermostat is closed which stops the water in the radiator overcooling and avoids the thermal cycling and associated shock that otherwise causes problems for a K Series.

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Once warmed up my gauge reads steady at just over 80 all year, any road and any weather. It may creep up to mid-high 80s after a run but drops back when the thermostat opens/fan kicks in. I have not changed the thermostat or drilled it and have always assumed it was an 82. The only times I have seen it get to 90 is after changing the coolant while the bubbles work their way out. 

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My first comment was too short.

It doesn't sound as if you have a major problem.

I have a pretty standard 1800. At the rebuild Ratrace asked what it was used for and on hearing it was road and occasional trackdays changed it to an 82° thermostat. That seems to work fine. Except that it runs too cold in winter on motorways etc.

I haven't drilled a hole in the thermostat but would be happy to if I had any problems. But I do warm it up rather gently.


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  • 1 month later...

Since posting this I have replaced the temperature sender and fitted a new 82 degree thermostat with a 2 mm hole drilled. [the previous thermostat was 82 degrees but not drilled.]

The car does seem to take more time to warm up but so far settles around the 80 degree mark.

What does concern me a bit is the routing of the pipe from the thermostat housing to the heater. It seems to rub against the stay that is bolted from the bottom of the engine to the inlet.Tbh I cant remember how it was before I fitted the new thermostat but I cant see an alternative route.  Is this normal or have I done anything wrong.

Thanks in advance





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Paul: if you decide to do the mod after reading Ian's PDF copy of the Low Flying article, I've got a piece of pipe to replace the submarine without a take-off for the header tank pipe, as I've since changed to a different coolant circuit with a PRRT. Yours for FREEEEEEEEEE because it's just clogging up my garage.

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