When driving my temp gauge (factory) will bounce between the first mark and the second mark. It gradually increases to the second mark then will fall back to the first and continue to do this while driving. The heat output will also vary during this fluctuation.

Could a bad thermostat cause this? How about the head gasket? I don't have any mixing of oil and coolant and no bubbling in the overflow bottle that i have noticed.

 

Could be the t-stat.

Whats the outisde temp like? Do you have the fan on still, covered rad?

Might just be the cold weather.

 

Mind does it to its the cold weather

 

its been in the 20s and 30s. it never did it in the past 3 winters i had the truck. the fan is still on the truck with nothing blocking the rad. I did not have these problems in past the heat always stayed a steady temp.

 

Have you changed the thermostat?

 

is the fan acting erratic or just the heat coming out?

 

I believe its normal because of the colder weather..now you notice it from the heat output. I wouldnt do anything with it.

 

My 93 does it and has terrible heat (probably bad heater core too). Does it all times of year but more noticeable in the winter months.

My 89 always runs too cool and has mediocre heat.

My plan is new thermostat

 

if everything is in order, these trucks should cook you out, especially in a summer-like 20 degree.situation. with some cardboard in front of the rad, my truck blows very warm air at 30 below and colder. Warmer than -30 its almost too hot. it sounds like a tstat to me also if its a gradual increase and decrease, if the gauge is twitchy its probally a ground.

 

Mine does it too, and a genuine Cummins thermostat made it worse.

I take the fan off.

 

I had a new stant t-stat in mine and I read how much better the cummins one was supposed to be so I switched it out and now my heat stinks.

 

So at what outside temps is it alright to run without a fan? I've been lazy on doing the electric fans on the single cab so it still has the mechanical on it. It's "winter" here in sunny AZ, 65 was the high for today.

 

do you think I will be ok without the fan when I am plowing? Perhaps I will try a new t-stat beings that it never did it before.

 

If you are plowing, I'd be real carful about running fanless.....

 

I had the same problem fluctuating gauge and no heat to speak of change thermostat. Both the cheap one from O'Reilly's, works great now. Mike