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Topic: Coolant temp gauge goes up when lights are on (Read 668 times) previous topic - next topic

Coolant temp gauge goes up when lights are on

One (little) thing that has bugged me since owning the coach is that as soon as I flip the headlight switch the coolant temp goes up about 8 degrees.  It's been like this since I've owned the coach.  The first couple of times I thought maybe the extra load on the electrical system was causing the alternator to work a little harder, thus causing the Cummins to run a little hotter.  But the more I thought about it, the less sense that made.  Also, it happens instantly. 

Basically it runs at about 181 to 182 degreees all the time, until I turn on the running/parking light, then within 1 second it's 189 to 190 degrees.

Anyone else have this issue?  Is there an easy fix, or should I just forget about it?

Thanks,
Douglas
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Douglas and Amanda
1997 40' U320 "Brawley"
2007 Ford Explorer Eddie Bauer
Motorcade #17266 Escapee #113692

Re: Coolant temp gauge goes up when lights are on

Reply #1 –
Quote from: ScubaGuy –
One (little) thing that has bugged me since owning the coach is that as soon as I flip the headlight switch the coolant temp goes up about 8 degrees.  It's been like this since I've owned the coach.  The first couple of times I thought maybe the extra load on the electrical system was causing the alternator to work a little harder, thus causing the Cummins to run a little hotter.  But the more I thought about it, the less sense that made.  Also, it happens instantly. 

Basically it runs at about 181 to 182 degreees all the time, until I turn on the running/parking light, then within 1 second it's 189 to 190 degrees.

Sounds electrical in nature, possibly grounding in the dash area.
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: Coolant temp gauge goes up when lights are on

Reply #2 –
Yup, a loose ground or inadequate ground for the instruments will cause this.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Coolant temp gauge goes up when lights are on

Reply #3 –
Ah yes mine does exactly the same thing.  I didn't figure out the mechanism right away.

Re: Coolant temp gauge goes up when lights are on

Reply #4 –
I have the same problem.  I can't remember which one now but one of the other gauges also moves with light switch.  Does the dash have single ground or does each gauge have hot and ground?

The knowledge on this forum amazes me and I do appreciate it.

Larry Bradley
1998 U 270
Larry Bradley
SOB
former 1998 U270
Build 5251
Jeep Grand Cherokee

Re: Coolant temp gauge goes up when lights are on

Reply #5 –
Mine does the same thing. I will let you know if and when I figure it out.

Mark
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Mark and Tanya
Milton , Florida
US Navy Veteran (DV)
1999 U270 Special 40' CAI , 2015 Jeep Wrangler Sahara

Re: Coolant temp gauge goes up when lights are on

Reply #6 –
Have not noticed that with the VMSpc display.

Re: Coolant temp gauge goes up when lights are on

Reply #7 –
Disconnect the luminescent dash inverter and see if it changes anything.
The selected media item is not currently available.Bill&Doris 97 U270 36'
University of Parris Island Class of 66
Semper Fi  Build# 5174 MC#17094

Re: Coolant temp gauge goes up when lights are on

Reply #8 –
Exactly same problem I have checked grounds and have not found a solution yet
2014 ih45  (4th Foretravel owned)
 1997 36' U295 Sold in 2020, owned for 19 years
  U240 36' Sold to insurance company after melting in garage fire
    33' Foretravel on Dodge Chassis  Sold very long time ago

Re: Coolant temp gauge goes up when lights are on

Reply #9 –
Both my 93, U225 and my current 93, U300 do the same thing. I changed the sending unit and the temp gauge on my U225 and it made no difference. I checked and cleaned any related grounds I could find but no change. It is related to the voltage. When the headlights go on the voltage at the dash drops by at least 0.2 volt which causes the temp gauge to go up as described. Don't know why but that's what it does.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Coolant temp gauge goes up when lights are on

Reply #10 –
I think the temperature gauge grounds through the temperature sensor on the engine. I think the problem may be caused by a voltage fluctuation, possibly from a weak ignition solenoid. I would bypass the solenoid and see if that fixes the problem and if so replace it or at least carry a spare solenoid because you'll need one pretty soon... I'm pretty sure the boost solenoid is the same as the ignition solenoid, at least on my coach, so you could swap them and see if that fixes it.
Scott Cook
1991 U300 36' 6V92TA
Old Town Penobscot 16
1984 Honda VF1100C (V65 Magna)

Re: Coolant temp gauge goes up when lights are on

Reply #11 –
Well I'm glad to know I'm not alone on this one.  Unfortunately I'm pretty busy for the next couple of weeks, so I'm just going hope someone with a shorter "To Do" list will work on this and post their results.

Scott's idea is probably a really good place to start.

Bill - my dash inverter is somewhere in the big bay, so in my case that didn't help.

The selected media item is not currently available.
Douglas and Amanda
1997 40' U320 "Brawley"
2007 Ford Explorer Eddie Bauer
Motorcade #17266 Escapee #113692

Re: Coolant temp gauge goes up when lights are on

Reply #12 –
Mine does the same thing, and the oil pressure goes down 10 lbs.
Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country

Re: Coolant temp gauge goes up when lights are on

Reply #14 –
I don't know if the Cummins grounds the temperature gauge through the sensor on the engine but my Detroit Diesel does. There's only one wire on the sensor and when you disconnect it the gauge goes to zero but when you ground it out, or when a torrential rain grounds it out, the gauge goes way up, sometimes all the way to the top, which I know can't be accurate because the transmission shows normal or slightly low temperature due to the rain... so that's why I doubt it's got a ground in the dashboard if it's wired the way my Detroit Diesel is... By the way, if your temperature gauge goes way up when driving in heavy rain, disconnect the terminal on the sensor, clean both sides, put it back together tight and seal it with Liquid Tape. It works great if you get it completely sealed. I did it a year ago and have driven through several heavy rainstorms with no crazy temperature readings... sorry if I hijacked your post for a moment there :)
Scott Cook
1991 U300 36' 6V92TA
Old Town Penobscot 16
1984 Honda VF1100C (V65 Magna)