overcooling/ no heat
 

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.

Yes I understand just tossing some info out not sure why my 2.5 gets hot fast even after the rebuild.

I agree that the stat needs to be checked. That would be my first line of attack but that was already mentioned. Sometimes it's a combination of things.

There is a similar thread entitled "3.9 takes forever to warm up".... and the ONE THING mentioned in that thread which has NOT been mentioned in this one is that the heater core MIGHT need to be flushed out. Of course you KNOW what a pain it is to get a heater core out. I will continue to watch this thread with interest because I am having similar problems with my '94 Dakota. The coolant just WILL NOT come up to the proper temperature, no matter what I do. And to my way of thinking once you install a new 195 degree thermostat there is just NO WAY that the coolant should stay at any temperature less than that. Seems that physics and thermodynamics both FAIL when it comes to Dakotas. I am stumped on this one - and I eagerly await the day when someone comes up with a logical scientific explanation for this phenomenon...... FredT

Ideologically, clogged heater core would actually cause the engine to warm up faster, at the loss of cabin heat.

The Heater Core receives circulating coolant at all times. Thus, the heater core functions as a miniature radiator at all times. Particularly if the cabin fan is on full speed heat, it could take the engine longer to warm up with a perfectly flowing/functioning heater core. If it's clogged, it will not shed that heat.

OK, now with that said. Our trucks use a 5/8" thermostat bypass hose. When we replaced the water pump on our Duramax LB7 last weekend, it uses a 1/4" thermostat bypass hose (and two thermostats).

The theory I have in mind may be that with the thermostat closed, the radiator is not heated, but when moving, cold air + wind chill is flowing past the block, which is having quite a bit of water circulate through the pump and heater core only. It's not a perfect theory, but I have to wonder is a 5/8" bypass hose is too big.

With that said, I have six 1/16" holes drilled in my 180 thermostat, and it has no problem getting up to temperature and opening. The small holes also help burp the system. I can watch the stat open and close on my OBD2 display - it will creep from 175 to 180 then back to 175 up to 180, and the stat opens, cools off, closes, heats up, and opens again.

Bypass hose simply allows coolant to circulate thru the engine when the stat is closed.... So far as I know, the stat is the ONLY path back to the radiator, from the engine.

Thanks for all the replys and sorry for the time to answer, didn't bookmark page and couldn't find thread at wrong forum.
So....some progress, bought another 195 stat and hung it in a pan of water and measured temp. Opened at 195, closed at 185. good so far. Replaced again and the needle now climbs up and TOUCHES the 2 in 210. Removed the hoses and flushed the heater core with the garden hose, first backflush was dirty and the flow looked good. Live in NE Ohio and temp has been in the mid 20s to 50's and air at outlets is no better than warm. Still not good heat to melt ice on window. Clutch fan is good. With radiator blocked a bad one would show change, it doesn't. With the rad. blocked I should overheat, no signs of that. Cardboard is between condenser and radiator. If the water pump had ALL the impeller fins dissolved there would be no water movement, and would have overheat in the heads and hopefully that indication on the guage. The upper radiator hose is hot on the bottom of the hose but cooler on the sides and top, there is a distinct difference. Leaky stat? Made in Israel
Going to change steering shaft tomorrow and will continue with the heat saga.

I know the full size trucks of that generation were a BEAR to get all the air out of the heater core.......