Engine temp. on M813 (cummins)

Today, I drove the 5 ton on a 70 mile journey to the sand/soda blasting company and had a great trip with the exception of one problem. Since I have not had this truck out on the road all that much, I kept a close eye on the guages. for about the first 50 miles, the truck ran at 200 degrees. Two miles on down the road, I looked over and the temperature guage was pegged out !! So I started slowing down to take some load off of the engine (Cummins 250) , and the guage acted as if it didnt know where it should be. It "jumped" back to 200 and it seemed that the guage was bad. It wasnt a gradual drop in temp but a very sudden jerk from 240 back to 200. I kept my eye on it and the it jerked back to 240 and stayed there. I checked the water and it had plenty. I was able to squeeze the top radiator hose about halfways and it was hot. I need help troubleshooting this. Does it sound like a cooling problem or a defective guage ?? The water from the pressure relief petcock was very black and nasty. There was no pressure on it, it just sortof dribbled out of this petcock. Sorry guys, I'm no shade tree mechanic. First thing when it comes home is a radiator flushing. Hope that you can understand what I am talking about.. Thanks for the help.

Chad

Chad

Flush it and when you have the coolant out of it. put a master gauge in it. If it's jupmping around. possibly a ground. If the fan is a direct drive, the temp should hug the stat. Could be a 160, 170, or 180.

the cummins in my 818 runs at 190* even under a load. might creep up to 195 on loooong grade with a good load.

Yep, planned on changing the thermostat as well

Make sure, if it's an electric gauge, that it is grounded well. A lot of the electric gauges ground through the gauge case to the instrument panel, and from there through the instrument panel to the dash board via the panel mounting screws. Lots of potential for a false reading, though I'm not sure whether an ungrounded gauge would peg to max or drop to zero...



Regards,
Jon

Along with the electrical checks ,you might want to check the hoses.sometimes they get soft and will collapse causing a restriction in the cooling cuircit.get her hot, pop the hood and run up the rpm's.hold it at crusing rpm and watch the hose's.don't forget when you refill the coolant to use diesel grade coolant.it has additives to prevent oxigen bubbles from forming around cylinder sleeves.

I'll check all of these things when I get her back. Thanks. I appreciate the help.

Chad, I'll throw my two cents in here. The first thing I'd do, even before driving it home, is to drain all of the old crap out of it. Once drained, go buy a good quality mechanical temperature gauge. Take out the old sensor in the water jacket and install the new one. Run, temporarily, the line into the cab so you can keep an eye on it. So long as it's not going to be freezing any time soon, go to your heavy truck parts store or Cummins dealership and get some motor flush suitable for your Cummins. While your at the Cummins dealership, buy the Cummins Coolant that pre-mixed and includes the additive to keep your cylinder liners from etching. Yes, this coolant isn't cheap, but you get the exact right stuff when you put it in. Install the flush additive per the directions and run your truck up to temperature. Mechanical gauges do not lie; if it's really overheating, the mechanical gauge will show it. If the mechanical gauge shows overheating, troubleshoot the overheating problem. If the mechanical gauge does not show overheating, troubleshoot your electrical gauge problem. By the way, I run into that black "goop" in the radiator from my Hawaii trucks all the time. Good luck, Joe

Thanks Joe. I will try that. We have a Cummins dealer in Fort Worth so I will stop by there in the truck on my way back home. Seems like all of our brush trucks are prone to overheat but they are one ton gassers. Lots of muck gets in the radiator. I a very partial to this M813 (even though it is not in service yet) but I think that it will be a valuable asset to our community once she starts fighting fires. Thanks for the input !!

M813 Radiator

I am working through almost the exact same problems. The gauge is still behaving the same way you describe, but what is more disturbing was the quantity of ENGINE OIL in the coolant. The engine oil cooler (heat exchanger) opened up and I could finally account for my non leaking, non-burning oil losses. It took multiple flushes and hours of standing by to do it until the oil was washed out of the cooling jacket and so was the rust. Having also changed the thermostat and temp sending unit, I find that the radiator is cold at the bottom and very hot at the top and think that the radiator is clogged. Check that old coolant for oil. You can feel it and also see the sheen on the surface.

Will follow up with more steps as they happen.

The radiator should be cooler at the bottom than it is the top if it's working properly. The bottom shouldn't be cold at operating temp though. If your gauge is pegging out and falling back rather quickly it's more than likely a short in the wire going to the sender or the sender itself shorting out.