Forum Discussion

hotjag1's avatar
hotjag1
Explorer II
Oct 20, 2015

Low water light came on, but...

As I was going up a long grade the low water light came on but the temp gauge showed perfectly normal. Got to the top of the grade and pulled over to check everything. No coolant is leaking anywhere that I could see and the sight glass in the overflow tank was full(sight glass was completely green).

Tried shutting engine down and restarting, but that didn't change anything. Since the engine was running at 190 degrees like always, I drove about 20 miles to an RV park. I will check the coolant level in the morning when the engine is cold and see if the overflow tank is completely full.

In the meantime, has this happened to any of you? What possible reasons could cause the light to come on and still have the engine running cool?

I unplugged the sensor connector on the overflow tank and that didn't change anything, so I plugged it back in.

Thanks for any help on this.
Class A
  • hotjag1's avatar
    hotjag1
    Explorer II
    Oct 22, 2015
    45Ricochet wrote:
    Good luck with your sensor issue. Consider yourself somewhat lucky though in being able to get to some of these items. I see nothing but radiator :E
    Have you checked over on the Tiffin site?


    I do appreciate having a side radiator so I can get to everything from the rear of MH. I did check on the IRV2 forum. That is where I learned that several people have spent a lot of money and not cured this problem.

    When I get to warmer weather in about a week I am going to look for the Freightliner ECM. The Cummins ECM showed no codes.

    Thanks to the poster that identified which pins on the connector powered the coolant sensor.
  • Groover's avatar
    Groover
    Explorer II
    Oct 22, 2015
    Mine came on while climbing a 6% grade and the computer actually turned the engine off. Called Cummins and they said that the sensor was at the front of the engine and if you are even a little bit low you can get a bubble up front when going up a hill. I topped of the tank and was good to go. I later found that the lower hose clamp at the radiator was a little loose and I had a very slow drip there. Interestingly, Cummins told me to use plain old green ethelene glycol, not the long life stuff. I guess that goes along with their instruction not to use synthetic oil either.
  • 45Ricochet's avatar
    45Ricochet
    Explorer
    Oct 21, 2015
    Good luck with your sensor issue. Consider yourself somewhat lucky though in being able to get to some of these items. I see nothing but radiator :E
    Have you checked over on the Tiffin site?
  • JackMS's avatar
    JackMS
    Explorer
    Oct 21, 2015
    I just looked on our insite program and it seems there are a few variations of the isl. The isl 8.9 CM850 seemed most likely for a motorhome. The coolant level sensor connects to pin 28 and 32 of the oem harness. Hope that helps.
  • JackMS's avatar
    JackMS
    Explorer
    Oct 21, 2015
    The 2 wires from the sensor most likely go to the OEM plug on the ecm. You would need a schematic which you can probably find on line You would have to cut the 2 wires coming out of the ecm and connect your temporary wire to them
  • hotjag1's avatar
    hotjag1
    Explorer II
    Oct 21, 2015
    CA Traveler wrote:
    Another option is to replace the sensor wiring with temporary wiring and if that solves the problem make it permanent. You could even run the temporary wiring through a hatch/window and inside the MH.


    That sounds like a good idea, but how do I determine which pole on the sensor is positive or negative, or does it make any difference?
  • CA_Traveler's avatar
    CA_Traveler
    Explorer III
    Oct 21, 2015
    Another option is to replace the sensor wiring with temporary wiring and if that solves the problem make it permanent. You could even run the temporary wiring through a hatch/window and inside the MH.
  • hotjag1's avatar
    hotjag1
    Explorer II
    Oct 21, 2015
    I would prefer to have the sensor working correctly too, but I have read on another forum that several people have spent a thousand or more dollars and still not found the problem.

    Cummins did check for codes and were not able to find anything Cummins related. They told me that it must be in the Freightliner chassis wiring.
    I am in Montana right now and it is cold. When I get further south, I will do as suggested and check all ground connections on the frame.

    Thanks for all the help and suggestions...Don

    Also, the engine has plenty of power, so it is not being derated because of the low water level light coming on. I'm glad about that:)
  • JackMS's avatar
    JackMS
    Explorer
    Oct 21, 2015
    My experience is on 18 wheelers. Without a program to actually check the code, we try a simple check. If the ecm is programmed to shutdown the engine for low coolant and that is what it is doing, if you unplug the sensor the fault will change from "coolant level low" to "voltage low" . The engine will not shutdown for that.

    Has anyone checked the actual code? I'm assuming it is level low since the buzzer is going off also. Kind of weird for a wiring problem to give coolant level low code. If no one has read the codes that may help if you are interested in fixing the problem. I prefer to have the sensor working in case of a big leak sometimes you will lose water so fast that the temp sensor will not catch the high temp.

    Electrical problems suck though. I see crazy stuff every day. Just when you think something can't happen, it does.
  • 11178adm's avatar
    11178adm
    Explorer
    Oct 21, 2015
    check the engine grounds from engine to frame there are probably some ground studs on the inside of the frame rails that will have several wires attached they can get corrosion and cause this problem
    also the coolant sensor works from resistance in the coolant to determine coolant level if it has been a long time sense the coolant has been changed or if it has been contaminated this may not be the answer but it is something to check. the check engine light on will not harm the engine as long as the engine temp is ok but it may depending on the ecm is programed it may derate the engine power

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