RWD - B 20 thermostat recommendations

Volvo RWD 140-160 Forum

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B 20 thermostat recommendations 140-160

A rather protracted follow-up on this thermostat question. We had a rather dry winter here so conditions dried early allowing a resumption of the vintage Volvo driving season with air temperatures that were definitely on the cool side. Same thing as mentioned on my very first post, driving at around 80 km/hr with outside temperatures in the -5 C range, the dash temperature gauge is reading in the low 70 C range.

It was a nice day today so I decided to pull the thermostat and check its operation. The thermostat is a Calorostat 82C. I did the immerse in water bath test with a thermocouple to measure the temperature right inside the top part of the thermostat housing. The thermostat starts to open around 81-82 C and is definitely as open as it gets by 90 C. So, the start of open and fully open temperatures appear to comply with the values for the type 2 thermostat in the Volvo service manual.

I let the temperature of the bath drop slowly and the thermostat does not appear to go fully closed until about 78 C, so there does appear to be a little hysteresis or the thermostat is just very slow to respond as the temperature is dropping. Out of curiosity, I checked the depth of the by-pass tube and the movement of the flap on the bottom of the thermostat and the by pass is open when cold and definitely sealed off when the thermostat is at 90 C. It was not practical to determine at what temperature the flap would close off the by-pass because as soon as you pull it out of the bath the thermostat temperature starts dropping and the flap starts moving.

With the thermostat in the closed position I pulled it out of the bath and confirmed that the center plate is closing tightly with the surrounding flange. So, with the exception of the jiggle valve there is no material leakage through the thermostat itself. I examined the thermostat gasket and there were no obvious signs of leakage around the gasket.

I am left with the conclusion that the thermostat is operating as designed and that I do not have an obvious leakage problem. I am further left with the conclusion that if you are running the heater at max on a really cold day at speeds over 80 km/hr you will struggle to meet the design operating temperature (82 C - 90C) for the engine. Since the measurements suggest that my coolant temperature was running below the fully closed temperature of the thermostat, the old school thought of putting in a hotter thermostat would not appear to offer a solution. I speculate that on the 140, at highway speeds there is enough cold air flow through the rad and the engine compartment that convective cooling of the engine block by ambient air combined with the interior heater operation is preventing the engine from maintaining its design temperatures.

Volvo used to sell cold weather black vinyl closures for the 140 that would clip on to the front grill. the closures had little flaps you could open for warmer day operation. I think these probably worked because they reduced air flow through the engine compartment and convective cooling of the block. If I want heat on cold days I think I am going to have to find one of those old grill covers.


New 1 B 20 thermostat recommendations [140-160]
posted by  142 guy  on Tue Oct 31 20:24 CST 2017 >

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