Farm Equipment - 200 Temp gauge stops reading at high rpm

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200 Temp gauge stops reading at high rpm

Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=202749
Printed Date: 23 Nov 2024 at 12:42pm
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Topic: 200 Temp gauge stops reading at high rpm

Posted By: pdh
Subject: 200 Temp gauge stops reading at high rpm
Date Posted: 17 Aug 2024 at 4:47pm

Working out a few glitches on a new to me 200 with righ at 3000 hours. Temp gauge seems to work at low RPM - but starts bouncing as RPMS increase and falls all the way to cold at full RPM. Looks to be original gauge. Maybe 50 years it all its got in it and its time for a new one? I usually start all electrical quests with the assumption of a bad ground and will check that out after I pull the cowl off - but other trouble shooting ideas while I have it off are welcome. TIA.

Replies:

Posted By: plummerscarin
Date Posted: 17 Aug 2024 at 7:04pm

Can I assume the coolant system is full? I know, dumb question but it first came to mind and is newly acquired

Posted By: 8070nc
Date Posted: 17 Aug 2024 at 7:06pm

Id check the wire from the sensor in the thermostat housing and make sure its not grounding somewhere

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1984 80780
1957 D14
DES 300 with 25000 engine
616 tractor

Posted By: KJCHRIS
Date Posted: 17 Aug 2024 at 7:30pm

Check the wire to temp sensor, unhook from sensor and operate tractor what does temp gauge do at differing RPM's then use a jumper wire to ground the wire and repeat process.

IF temp gauge varies its readings I'd go with bad wire or bad gauge.

IF temp gauge stays in steady position either high or low, I'd replace the sensor.

I've replaced a few sensors in 185 & 200 tractors but never the gauge itself.

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AC 200, CAH, AC185D bareback, AC 180D bareback, D17 III, WF. D17 Blackbar grill, NF. D15 SFW. Case 1175 CAH, Bobcat 543B,

Posted By: Lars(wi)
Date Posted: 17 Aug 2024 at 7:54pm

Increased rpm’s is creating more air movement, thus resulting in poor connection of the wire on the sensor.

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I tried to follow the science, but it was not there. I then followed the money, and that’s where I found the science.

Posted By: pdh
Date Posted: 17 Aug 2024 at 8:19pm

Yes coolant is full.

Posted By: pdh
Date Posted: 17 Aug 2024 at 8:21pm

Will focus on connections at the gauge and the wire from sensor to gauge and see what I find. Thanks all.

Posted By: DaveKamp
Date Posted: 18 Aug 2024 at 7:43pm

I would start by putting a pressure test gauge on the coolant cap, and fire it up, idle for just a few seconds, then bring it up to full governed, then back down, then back up, and see what that gauge does... cold coolant won't generate any vapor pressure, but combustion pressure leaking into the cooling system can cause bubbles to accumulate, and if they accumulate around the sensor, it will not read coolant temperature properly.

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Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.

Posted By: pdh
Date Posted: 18 Aug 2024 at 9:01pm

Thanks for all the ideas. Sensor seemed a little rusty and the push on connector seened a little loose - so I cleaned up the sensor and tightened the push on a bit - ran it around some to bring it up to operating temp. Erratic reading is gone and now getting a consistent temp reading that stays steady through all RPMS albeit a iittle on the cool side - so guessing the thermostat is stuck open. I will put getting a new stat in it before I put it to work on the auger this fall - but for now i think that issue is resolved. Much obliged.