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Testing a Temp Gauge
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FREEDGUY View Drop Down
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Joined: 15 Apr 2017
Location: South West Mich
Points: 5396 		Post Options Post Options   Thanks (0) Thanks(0)   Quote FREEDGUY Quote  Post ReplyReply Direct Link To This Post Topic: Testing a Temp Gauge
    Posted: 08 Jun 2019 at 11:04pm
Is there a way to "test" a temp gauge or the sending unit? Planted today with a gasser 180 that the needle on the gauge never got above the middle of the "white" section of what I am pretty confident is the original A/C gauge. I took a few readings with an I/R thermometer and got 195* on the block, 197 on lower radiator hose but only 118 on the 'stat housing?? Never boiled over and never "smelled" over/heated. Thanks
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youngorange2000 View Drop Down
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Joined: 27 Mar 2019
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Points: 314 		Post Options Post Options   Thanks (0) Thanks(0)   Quote youngorange2000 Quote  Post ReplyReply Direct Link To This Post Posted: 08 Jun 2019 at 11:58pm
I have used a stove pot of hot water before while holding it with a needle nose pliers. also if it was hot out or if you were running for a while( engine on for over 45 mins straight) it could be "sweating" heat off the block, 118* at the upper should be about right if its got a 160* thermostat,thats whats in my 190 I don't know about a 180 for sure. I would just keep fresh coolant in it and keep an eye on it    Just my $0.02
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DaveKamp View Drop Down
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Points: 5971 		Post Options Post Options   Thanks (0) Thanks(0)   Quote DaveKamp Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jun 2019 at 3:47am
Testing the temperature gauge for proper operation is best done by unscrewing the sending unit from the block, and putting a temporary table alongside the tractor such that you can put a hotplate with pan of water in reach of lowering the sending unit into the hotplate, then boil the water.  At your elevation, the boiling point will be close enough to 212f for the temperature gauge to read about that... and then fall gradually as it cools.  You can place a confectioner's thermometer in the pain and compare readings between the temp gauge and thermometer as it cools, and it should track okay.  if it does, then your gauge is working fairly well.  Generally, mechanical gauges either function fine, or don't function properly at all.
Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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I tossed an aftermarket temp unit into 'Troy' and after cleaning the rad, new 50/50 mix, stata,hoses ,etc. came to the conclusion the gauge unit is 'slow'. The needle moves up OK, but then gets 'pegged' at 220 for a long time, then slooooooowly goes down to 180, then repeats this 'cycle'. Scanning the block and rad with an LCD temp 'gun' shows everythings fine so I have to conclude the guage is at fault. Maybe too much mechanical tension on the dial guts? If I was super concerned I'd buy another and try it.

Jay
3 D-14s,A-C forklift, B-112
Kubota BX23S lil' TOOT( The Other Orange Tractor)

Never burn your bridges, unless you can walk on water
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DaveKamp View Drop Down
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Originally posted by jaybmiller jaybmiller wrote:

me to the conclusion the gauge unit is 'slow'. ...Maybe too much mechanical tension on the dial guts? If I was super concerned I'd buy another and try it.


That's about the best SIMPLE way to put it, Jay.  Typically mechanical temperature gauges work in one of two ways- first is by conducting heat from the sensor end to a bimetallic strip inside the gauge, the other, is by having some sort of expanding material exert pressure on a bourdon tube:

https://www.flowcontrolnetwork.com/what-is-a-bourdon-tube/

If you cut open most mechanical temp gauges, you'll find that the 'sensor' end has a waxy substance in it... and that's what it is... a type of paraffin... and it's probably solid.  When warmed, it liquifies AND expands, and because of the volume of space inside that end, it will expand some known amount from starting to ending temperature, and that expansion exerts pressure on the Bourdon tube inside the gauge, causing it to deflect, and pull (either directly, or by a lever or gear segment) the pointer.

Frequently, gauge failures are due to a crimp in the tube somewhere, the rest are probably due to the lever or gear wear or contamination.
Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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