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)?

[Gaz2]

When I read the post's title, I though it was asking if it's warm enough yet to go swimming in Lake Windermere!

[sleek lemur]

Wiring.jpg

Voltage Stabiliser.jpg

Something unexpected. The voltage stabilizer is not connected and I see green/white wires directly joined to the blue through some sort of sleeve. Hope this shows in the attached pics. Am pretty sure the wires shown should be attached to the voltage stabilizer as one of the blue ones goes directly to the oil temp gauge.

Question is, which wires connect to which terminal on the voltage stabilizer?

I suppose I should expect that the stabilizer is faulty, as I can't think of any other reason why someone would have performed the barbarity described above.

Many thanks in advance.

[Ron Kwas]

sl;

Symptoms of failure of V-Stab are possibly complicated and different for each instrument, because of the different time constants of the instrument (I expect Fuel Gauge has the longest, as it must accommodate a bouncing float due to fuel sloshing)...I have not specifically studied them to give better examples and explanations, BUT... if V-Stab has been bypassed (which someone undoubtedly has done here, by tying Wht-Grn[Input] to Blu[Output]), function of all gauges supplied by this node would be that of the failed (always ON) part of V-Stab ON/OFF cycle, which means that YOU have just found the cause of your "wild" Temp Gauge readings, and at the same time, that "complicated and different " symptom I spoke of...

To address your comment: "fuel and oil temp gauges are working ok" ...former "working OK" can be explained by the super long instrument time constant I spoke of above, and the later's "working OK" is actually not correct...it just seemed to you to be working OK, and you interpreted it as such!...I bet you never verified the calibration and accuracy of the temp indicated...you just got used to the typical readings while gauge was being supplied with a constant 12V, opposed to the 12V for only 83.3% of the time it should have been...I would say you'll have to get used to a new "typical indication" of the Oil Temp gauge (not to mention the Water Temp and probably even Fuel Gauge) after you install a replacement V-Stab!

...now if I can only get you to elaborate and specifically describe what you meant by "wild water Temp readings", because this will be the best possible description of the failed V-Stab symptoms!!

Excerpt of '71 1800E WD showing V-Stab and associated:


Reference: https://www.sw-em.com/voltage_stabilizer.htm

This is without a doubt a unique learning experience for the V-Stab supplied instruments, and I expect to add much of it to the V-Stab page.

That concludes today's CIS Goteborg session!

Cheers!

[sleek lemur]

Thanks Ron. All back together now (apart from one knurled nut for the rev counter, which slipped thru my fingers and has buried itself in the under-dash spaghetti). Now that it's fixed, the cause has become apparent. The car was taken back to bare shell by the people I bought it from in Denmark. Obviously, they joined the WG and Bl wires on dismantling and simply failed to reconnect. This is the latest in a long list of things they bodged.

I'm so grateful for your help. it was you saying in another post to Graham where you told him to chase the WG and Bl leads that unlocked the mystery.

AND now I think of it, when I recently changed the fuel tank as part of the conversion to Webers, the fellow doing the job (123GT on this forum - I will write a post about the great work he did) remarked how there was only a minute drop of fuel left in the tank. Well, I had run it low on purpose, but clearly it was a lot lower than I thought!

Haven't checked the temp gauge yet, as I also have a small issue with the electric fan, but I am sure that this has sorted the problem. Previously, it was right off the gauge within 5 mins of starting the car and before the thermostat had opened.

Thank you, O King of the Voltage Stabilizer and thanks also to 123GT for emailing pics to me this afternoon.