Archived 99 coolant temp low.. ?? Thoughts?

[David_VT]

Hi all,

I wanted to do a sanity check with the members on what I am seeing my 99 doing. . Please breeze through this and share your thoughts. Thank you. While I am not afraid of being under the hood and doing things like changing injectors, I am no first rate diagnostic mechanic by any means.



The other day our air temp in Vermont jumped from teens to 40's. Normally that would be a good thing...



It was mid 40's(F) friday and I realized I'd been driving with my winter radiator shield still in the eng compartment. This is a very thin sheet of paneling with about a 10" hole in the center that I've used for several winters. I slide it between the intercooler and radiator on my 2nd Gen.



I stopped, pulled out the board and continued on my way... . What I then saw was the temp gauge gradually drop from the high side of normal and go all the way down to the 140 peg. I thought, good job on removing the wind blockage...



The rest of that short trip the gauge never came off the peg or maybe moved a tiny bit.



Saturday morning I thought about this and checked the antifreeze level. It looked ok, just below the cap and several inches in the overflow tank. I drove it once over the weekend and still saw no movement in the temp gauge.



This AM I did a short drive to warm up the truck and started to dig deeper thinking thermostat,pump,sensor, etc.



The upper hose was hard with pressure. The radiator itself is warm/hot to the touch. The gauge is dead on the low 'peg'. If I squeeze any coolant hose under the hood I feel it in all other locations. The heater in the cab seems to blow warm but not super hot.



After cooling a bit, I ran with the radiator cap off for a few minutes thinking I had build up air in the block or hoses somewhere (I have an espar mounted low on the frame). Perhaps it went down a 1/2 inch so I added a little fluid to top off the radiator. No change in the temp gauge.



ANYONE KNOW A SIMPLE ELECTRICAL WAY TO TEST THE COOLANT SENSOR which I believe is located in the front of the block near where the top hose connects? It and it's wiring are nowhere near where the radiator cover had been but who knows?



ANYONE KNOW OF A DIAGNOSTIC METHOD I've missed that will help narrow this down?



ANYONE THINK I WILL LIKELY DAMAGE the truck if I continue to drive it in this condition for short trips (10 minutes to work, store, etc)?? (until I fix it right). We are in mud season now and I need the 4x4 real bad.



Thanks for any thoughts on this one...

 

[RustyJC]

The thermostat is probably stuck open. Pretty common problem on the B-series Cummins.



Rusty

 

[TowPro]

Well its not doing the truck any harm, but they do like running better warmed up, and it helps dry out the exhaust.



Have you ever replaced the termostat? Its an easy job. you could remove it and test it in a pot of water on the stove and a therometer, or just replace it if its the original.

 

[David_VT]

Thanks, I suspect you are correct that it is the tstat being stuck open.

Just now I 'slogged' my way up a hill through the mud while returning from lunch and I did see the temp gauge start to deflect up slightly with a corresponding mild increase in cab heater output.

David

 

[JFaughn]

You can get a thermomiter with a 6-8" shaft from a tool supply and stick in rad cap hole to check , then for a little more a electric gun that uses inferred to tell the temp ,

 

[David_VT]

Thanks all...

I put the winter front back in and the gauge came right back up upon driving. . To me that confirms the thermostat as being the problem.



I had a hard time getting a thermostat from the parts store and had to go to DC to verify the 98 and 99 part numbers where the same. The parts store then sold me a tstat from the 98 which matched the numbers. 180degrees but no gasket. . arggg



Thanks again!