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Installed a Napa / VDO Capillary Temp gauge in the plow truck last fall (broke the tubing in the old stewart warner). Worked like a charm for a while. Now the gauge does not seem to work and the needle never rises.
Truck runs fine – idle it for 10 or 15 minutes on a 20 degree day and the coolant in the radiator reads 190 F (Don’t tell the girlfriend that I used the meat thermometer).

Just pulled the gauge out and decided to check it with some hot water on the stove. Now it seems to work. Has a little hiccup from 120 to 160 – or at least it reads low compared to the meat thermometer. At 180 to 210 it is spot on compared to the meat thermo.

So now I am wondering if the gauge is going dry? Anybody else ever have this problem.
In other coolant things – I have a block heater that runs from the coolant drain to the coolant fitting by #6 on the cylinder head.

Engine was pulled last winter and I did a quick ring and valve job. Did not pull the water distribution tube due to lack of time and it looked pretty good. Last time I checked the radiator was full of coolant – did not check when I pulled the gauge. But I did drain like 3 gallons of coolant.

Any thoughts.

The gauge is under warranty so I could bring it back for exchange or just put it back in and see what happens. My goal being a working gauge - with the least amount of time turning a wrench in the snow.

Thanks
Jim

If the gauge reads 0 in the engine and works on the stove in the pot of water then your issue is in the engine. When you pulled the probe out did coolant run out?

Yes I had some coolant drain from the gauge plumbing at the block.

Did an initial coolant drain – loosened the gauge – coolant leaked out - retightened and drained some more coolant from the block. Did have some black grime intermixed with the coolant from the gauge port which I was surprised to see.

But the coolant that leaked out could have been what was trapped in the gauge plumbing - it goes from 1/4 up to 1/2 via a pile of adapters and reducers and then back down for the gauge bulb.
But as I recall there was some "gravity" pressure behind it.


In some ways I also would have thought even a dry gauge would read something above 120 after plowing for 45 minutes. The steel surrounding the gauge is certainly hotter then that. Maybe I'll go try the gauge touching the woodstove and see what it reads.

Jim

Now you are confusing me. You said in the beginning the gauge needle did not rise and now you say that it rises to 120????

If the needle was dead in the engine and alive in the pot on the stove then the engine is the fault.

If the gauge was only rising to 120 while plowing snow for 45 minutes then the next question is what was the outside air temp? What rating thermostat are you using?

I can run my M for an hour moving round bales at 0 degrees and never have a temp above 135. It runs about 160-165 in the warm months.

Sorry Cuz didn't mean to mislead.

The lowest reading on the gauge is 120 or maybe just a hair lower. The gauge is a 115 to 260. And watching the gauge on the pot on top of the stove it is a little sluggish in lower temps.

I suspect the engine as well - just cant figure out why. The gauge port is open - no crud. I have also compared the numbers and time to run up to temperature on my other M37.
And in the dead of winter it takes about 5 minutes to start showing 160 plus or so on the gauge, which was also the case with the plow truck prior to the gauge not reading.
With both trucks showing swirling coolant in the radiator.

I put the probe on the wood stove last night just to see what a metal to metal contact would read. With a woodstove surface temp of 200 -220 the gauge would read about 130 to 150 depending how much surface contact I had with the stove. Curious why that would not show in the truck even if the bulb was dry.


Jim

Update -
Reinstalled the gauge with some different adapters that let the probe stick into the block some more - before it was kind of on its own in the series of brass fittings that stuck out of the block.
Temp came up on the gauge to 160 F in 10 minutes at idle with it being about 20 degrees F outside.

So I am baffled. I guess time will tell. Maybe the truck is mad that its has only plowed 3 times all winter and not the usual 2 to 3 times a week.
Just craving some love and attention.


Jim

Sometimes enough air gets trapped in the system to keep the coolant away from a certain area. When you refill the coolant it is a good idea to burp the system usually at the heater hose connection on the head. If not heater hoses then crack the temp sender loose until you get a flow of coolant.