army48ret@gmail.com Report post Posted April 1, 2011 In a 400 Cummings diesel pusher my engine heat gauge will allow the needle to creep up to just short of the line before the hot line. When the needle is about one width from the line it will drop back to the normal line. It may stay there two or three minutes before it starts the creep again. The needle never passes the line above normal and never comes close to the hot line. I'm thinking a thermostat is sticking or a bad gauge. I replaced the radiator cap, a five dollar fix if it had worked, which did not fix the problem. Any suggestions? Share this post Link to post Share on other sites
Guest BillAdams Report post Posted April 1, 2011 I suspect that you have a hydraulic radiator fan and the thermostat that controls when the fan comes on and off is either faulty or set to the wrong parameters. Share this post Link to post Share on other sites
MikeCanter Report post Posted April 1, 2011 I suspect that you have a hydraulic radiator fan and the thermostat that controls when the fan comes on and off is either faulty or set to the wrong parameters. I believe what you are seeing on the needle going up then back down is the thermostat opening and closing. I the thermostat was bad and stuck open then it would alway run too cool or if stuck closed would keep heating up until it boiled. The temp is cycling at a indiacted high temp which if the gauge is correct is higher than what the thermostat temp is so maybe what you are seeing is the cycling of the cooling fan. You should be able to tell if it is the fan cycling by standing out by the side and seeing if the fan is coming on and off. If it is the fan cycling and matching the movement of the needle then I agree with what Bill said. Share this post Link to post Share on other sites
wolfe10 Report post Posted April 1, 2011 First, has the coach always done this? If so, it is likely just a Bill said, the difference in "thermostat fully open" (low needle position) and "cooling fans kick to high speed" (high needle position). Check with your chassis maker-- most have a wire that can be disconnected that causes the hydraulic fan to remain on high speed. Do this and see if it stabilizes your temperature readings. If so, it may be normal or may be a "not sensitive enough" controller for the hydraulic fan. Though it could be a thermostat, your description is that of specific high/low readings. A sticking thermostat is unlikely to always stick/release at exactly the same temperatures. Brett Share this post Link to post Share on other sites
army48ret@gmail.com Report post Posted April 2, 2011 Thanks for the advice. This is my first post and I was amazed at the quick replies. Thanks again and I'll check on the fan asap. Chuck Share this post Link to post Share on other sites
