1800: Wild water temp readings

[sleek lemur]

Hi All, water temp gauge on my 1970 1800E was showing very variable readings. It would quickly rise to very near the red and then hover about in the top 80% of the dial, going dangerously near the red as soon as I slowed. The engine is newly rebuilt, as is the radiator. It doesn't feel like it's running particularly hot. I bought a new sensor, part no 683299 and now the temp gauge goes hot off the scale and stays there! The new sensor is rather chunkier than the old one and whereas the old one screwed right down to the nut, the new one doesn't screw in as far, leaving some 5mm thread showing (though doesn't leak of course).

Any suggestions from my usual correspondents gratefully received !

[Clan]

Originally Posted by sleek lemur

Hi All, water temp gauge on my 1970 1800E was showing very variable readings. It would quickly rise to very near the red and then hover about in the top 80% of the dial, going dangerously near the red as soon as I slowed. The engine is newly rebuilt, as is the radiator. It doesn't feel like it's running particularly hot. I bought a new sensor, part no 683299 and now the temp gauge goes hot off the scale and stays there! The new sensor is rather chunkier than the old one and whereas the old one screwed right down to the nut, the new one doesn't screw in as far, leaving some 5mm thread showing (though doesn't leak of course).

Any suggestions from my usual correspondents gratefully received !

I would say you have the wrong sender ... did you get it from a reputable volvo source ? check the engine and battery earths and the feed voltage to the TEMP gauge it should be around 10 volts average , it flickers on and off due to the voltage stabiliser but average voltage is 10V an analogue needle volt meter is best for checking this ..

[sleek lemur]

Thanks, Clan. Sender came from Brookhouse and the part number lines up with other suppliers. Will make the tests on the gauge as you suggest.

[NeilMurray]

Hello, I had a similar issue with the matching of my (new from Brookhouse) temperature sender to the gauge. I can't remember why I replaced it now, probably vanity as it was looking a liitle tarnished. I "solved" the issue, having first confirmed that she wasn't running hot, by making up an extension lead between the sender and the original cable, that includes a resistor (I can't recall the value now); some trial and error may be required in order to get the gauge to sit where you want it at normal temperature but it seems to work well and responds to fluctuations in temperature.

I think the sender is vdo and the gauge Smiths so maybe the resistance value of new senders is not tuned for our application?

[Derek UK]

#683299Looks to be correct for 1800E with the black-faced VDO gauges.

[sleek lemur]

Thanks very much to all. I will try the resistor route. Sounds like O-Level physics! Interesting what you say about the VDO gauge. Did they change from Smith's to VDO (or vice versa)?

[Derek UK]

Whoops, better correct my mistake here. Blackface gauges are indeed Smiths. I was thinking they change when they changed from the blue-faced gauges. Being an Amazon man I'm used to VDO gauges.

The later Smiths gauges changed from a filled capillary tube to an electrical sensor.

[sleek lemur]

So.....I've owned the car for only a few months. It's been rebuilt, but some strange things happening. They obviously didn't do a post-rebuild shake-down and also they've failed to do obvious stuff.

With the particular issue concerning this thread, I had the rad re-cored, replaced the 88 Deg thermostat with 77 and had a good go at bleeding the cooling system.

Big improvement. Car now drives at correct temp, however when stationary at tickover, the gauge quickly rises to the top of the green. When I rev the engine (still with the car stationary), the needle quickly falls back to normal. I don't even know, is this normal?

Many thanks for your patience with this!

[Clan]

Originally Posted by sleek lemur

So.....I've owned the car for only a few months. It's been rebuilt, but some strange things happening. They obviously didn't do a post-rebuild shake-down and also they've failed to do obvious stuff.

With the particular issue concerning this thread, I had the rad re-cored, replaced the 88 Deg thermostat with 77 and had a good go at bleeding the cooling system.

Big improvement. Car now drives at correct temp, however when stationary at tickover, the gauge quickly rises to the top of the green. When I rev the engine (still with the car stationary), the needle quickly falls back to normal. I don't even know, is this normal?

Many thanks for your patience with this!

I would suspect the thermostat you just fitted is sticking when it it is time to open , Please use the correct 88 or 92 C thermostat ,they will still be available from Volvo . otherwise the engine is going to run inefficiently and use more fuel and cause engine wear , condensation in the engine and oil and your heater will not be much good .. Have you still got the standard mechanical radiator fan? If the water pump is of dubious quality it may not have an efficient impeller , so much can happen with bodgers over a 50 year period , you cannot assume anything is correct ! the temp gauge should be stable in the centre at all times if everything is working properly .

[sleek lemur]

Thanks, Clan. I was actually told that 88 degree thermostat was too hot for UK summer and should swap for 77, which I did. Engine oil is nice and clean. No oil in water.

Using original fan, yes.

Sine the problem only occurs at tickover, am suspecting water pump. The engine has been rebuilt, but since owning the car, I have found a few corners that have been cut.

But I'd certainly prefer to investigate any other possibilities.