thankfully i havent had to post anything here in the past almost 2 years i think .... but now im back, my last diagnoses i used info from here to take with me to shop and boy did it help......hoping someone can help now.....

Sometimes when going up a hill(it doesnt have to be a grade or really steep hill but i notice it more on the steeper ones) it seems like i lose some power and its a noticeable difference, also when this happens my water temperature goes back and forth alot...it would be running at about 180degrees then itll drop down to maybe 140-150,,,,, then shoot back up to like 225-240 and make my high coolant warning light/buzzer go off....now keep in mind it doesnt do this all the time, and the times it does it lasts for a while. Like if it happens on a steep hill then i can still feel it on small hills, and then all of the sudden sometimes it kicks back in and starts pulling right.

i have a freightliner century class,,,,,,,

someone told me my thermostat maybe out or something........

one more thing......yesterday morning i started truck and it took a while for the temperature to get to operating range(warm up).....

 

let me also add that it doesnt do it all the time...i guess just when it wants to. For example it didnt do it any this week, i left charlotte went up fancy gap had a load that was 22k lbs and went up about 55-60mph....but last week i pulled the same exact load and it was acting up and went up fancy gap 40-45mph........

 

That is a tough one. It has been my experience that either the thermostat sticks open OR closed. Yours sounds like it is sticking open AND closed. Does the low power happen when temperature is low or high?

 

normal temperature range for normal running for my truck is 180-190......but when i see temperature gauge drop down to 150 or lower thats when problem starts........

 

Different fuel strategy for low temp operation from the computer. Change the t-stat and see what happens.

 

oh yes,,,might i add that i also thought it was a fuel problem cuz i went to fuel up apx 4000 miles after getting fuel filter changed and fuel filter was almost full(i have one of the davco see thur ones)......will definitely change thermostat this week and will update u guys and let you know.......THANKS for everyones help!

 

Thermostats do not usually make for sudden change in the cooling system temperature. So if you're watching your gauge spike between 180... 140... 240... that's not typical of a thermostat.

I would recommend a comparison between the actual engine temperature to the temp displayed on the dash gage, and also compare temp received by the ecm to temp displayed on the gage which is likely accurate as your warning lights and buzzers are activated.

High engine temperature will derate engine performance as an engine protection feature.

Is the coolant level changing; does it need to be topped up on occassion?

And again, someone has already mentioned the thermostat sticking open or closed... typically, the engine will run hot (overheat), or colder than normal (requiring long warm-up period).

 

so i should still replace the thermostat since it seems to be sticking?

 

How about the possibility of a bad ground between the engine and chassis, or a bad electrical connection somewhere in a wiring harness causing the erratic temp gauge readings, and at the same time either "confusing" the ECM, or intermittently interfering with the ECM's "instructions" to the injectors?

 

well heres what happened today....left charlotte, load is 20k lbs....done the problem i described in first post for about 3.5 hours and as soon as i got into atlanta it stopped, temp hand stopped moving around, sat at 190degrees and i had normal power all the way to hammond, LA.........

i noticed when temp gauge was at 140-150 thats when it seemed like i had least power(i had to downshift on a few very minor hills)

but when it sat at 190 it was like nuthin was wrong,,,, will keep u guys updated