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Possibly overheating volvo

415 Views 5 Replies 3 Participants Last post by  142 Guy
Hello all,
I purchased a 67 Volvo 122s wagon in February this year, since then I have been doing some maintenance items on the car. after doing all service measures, oil, coolant, new radiator, hoses, belt, plugs, rebuild distributor, valve adjustment and rebuilding the carbs… etc. it is all together.
However, now the cars temp sensor is showing it overheating while idling for 3 minutes. While driving, it will keep at around 3/4-5/8. We were tuning the carbs and the sensor shot way up but the car itself had no signs of overheating. When idling and revving the engine after it showed it was hot, the temp sensor shot back up to the middle position, almost like it was a direct reaction to tapping the throttle.
I am clueless on what the issue could be, there’s a new thermostat, and the temp sensor appears to be working well when we tested it in hot water.
Any advice is greatly appreciated on how to fix the temp sensor or if there are any ideas on what could cause the spike/quick drop in temperature.
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For the complete 'scoop', go here:

SW-EM Temperature Gauge Notes

The original gauges are mechanical so they don't really 'shoot up' like an electrical gauge can if you get a short on the wiring. Do you still have the original mechanical style gauge. If so, read through the discussion on the Swedish Embassy site. If you have a retrofit electrical gauge, I would start looking for a short circuit in the sensor wiring. A short to ground on the sensor wire typically causes the gauge to read full scale.
A simple test. At idle, open up the heater valve. The flow to the heater is out the back of the head and this increased coolant flow typically drops the measured temperature at the back of the head. The same thing happens on a hot day when you take off from a traffic light due to the increased coolant flow as the pump speed increases. Normally, the temperature gauges are damped or have a bit of a dead band so these temperature fluctuation are not so obvious.

The temperature fluctuations can be exacerbated by a loose coolant distribution pipe in the head. Ron K's web site has a discussion of the distribution pipe. If the pipe comes loose coolant can bypass the pipe so that at lower engine speeds the back of the head does not get sufficient coolant flow. As I recall, if you drop the coolant level and remove the thermostat you can see the distribution pipe in the head and should be able to tell whether it has come loose or rotated out of position.
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