New to me 97 dakota 3.9l eng. low heat guage just inside normal range. Changed thermostat 195 temp. increased 1 needle thickness. Warm air at outlets. covered radiator with cardboard 80% no change. heater inlet158,outlet 140, upper rad hose at therm. housing 152, at rad 134, rad outlet 112, water pump inlet 95. Saw similar condition on 86 chev. with cat. removed. Reinstalled cat. conv. heat came back. Any solutions?

 

Cat has nothing to do with it. You have a bad thermostat, or, its installed wrong. Buy a good quality stat. (stant is a good bet.) Do NOT buy one of the 'safety stats', they fail far to quickly.

 

Clutch fan may also be stuck on engaged. Does the engine roar a lot?

 

Even so, the engine should get up to temp.....

 

20 degree loss across the top hose, and another 20 degree loss across the radiator? That doesn't sound right at all. How cold is it outside, single digits?

The 3.9 lacks 2 heat-generating cylinders but has the came cooling system as a V8, so it is somewhat cold-natured. But that just don't sound right.

 

I'm with Dodgevity clutch fan frozen/stuck on.

He also must live in a very cold place for those temps.

 

Even if the fan clutch was seized, the thermostat should still get the engine up to temp. After all, it won't let coolant circulate until it gets to temp..... which it never does..... So, unless its REALLY cold out, the stat has failed.

 

This may sound strange but I use a 180 stat and get heat out of the vents faster than when I used the 195 stat.

On the possible stuck fan I have experience with that the 2.5 only has an efan so during the summer with the A/C running my efan is on all the time and even in 110 heat it can keep my coolant temp low almost exactly 180 to 185 but I like it running a little cool in 110 heat. I keep the 180 because when I used the 195 I had overheating problems if not running the A/C especially in traffic it overheated all the time with no airflow past the rad too keep it cool I needed to be going 40 mph or it overheated. I blew-up 1 rad a year because of this even with proper coolant.

He must live in a very cold place.

 

The 20 degree drop across the upper hose and 20 further across the radiator indicates that the coolant is flowing; so yes, the stat is leaking in some amount. I have six 5/32 holes drilled in my stat for specific reasons. Have never checked to see what my thermal bleed is though.

But with a full winter front, an engaged clutch fan would be terribly inefficient and wouldn't cool much at all, I would not think. Depends on how tightly it is placed.

"technically", and this is a really long grasp, it is mechanically possible for the intake manifold to be heat soaked enough to open a 180 stat but the water only measure 150 at the outlet. It would have to be windy and single digits. But I can't see it heat soaking a 195 and being 150 at the outlet.

NOW....There is one other potential. I don't like it.

The water pump could have all but completely failed...if the water isn't moving, or is moving slowly, it can lead to all kinds of weird things happening.

 

97 3.9 will be clutch fan only, no Efan.