View Full Version : Thermostat

12-11-2008, 10:44 AM
I have an inquiry. Every year I go through the same problem where my thermostat locks open and causes me to get no hot air in the vents. It also does this a few weeks into winter when it get REALLY cold and I need it more than ever.

I've purchased a higher temperature thermostat thinking that something might be overheating causing it to lock open, but if that were the case, then why does it only do it in the winter?

Anyway, I'm hoping someone can help me figure out why my van hates me and likes for me to freeze while driving.

BTW, it's a 1991 Dodge Caravan 3.0L V6 engine.

Thanks in advance.

Barry Morris
12-11-2008, 10:48 AM
I would suggest that something is frozen in the heater controls, not the thermostat.

After the van is warmed up on a cold day, pop the hood and put your hand on the upper rad hose. It should be hot enough for you not to want to hold on too long, but not cool and not hot enough to burn you quickly. Just a rough check on engine heat, but it works.

I sometimes pay the local garage a few bucks t park my vehicle inside over night, just to thaw out mid-winter. That often helps oddball little problems.

12-12-2008, 12:37 PM
Could it not be an air lock? In the summer with heat and expansion it would force a flow, while in the winter the motor remains cool and won't pump the air. Low coolant can also cause similar problems, the Chrysler four cylinder vans where bad for that. At an idle they blew cold but rev it up and you got heat.

Barry Morris
12-12-2008, 04:17 PM
So where did the air come from???

I think the Dodges had a problem sometimes when the heater core was higher than the rad.

Here's an idea, and be damned careful. Check the water level, engine hot, AND running. You CAN pull the cap off safely and check the antifreeze level like this if you follow this.

Engine warmed and running. Check the upper hose, should NOT be so hot it's likely to burn you right away. If it's OK, us a rag folded two or three times and SLOWLY open the rad cap to the first stop. (you might want to try feeling for this earlier when the engine is cold). You should get a short shot of fluid coming out, but not much. Once the pressure is released, pull the cap off, keping the rag on it. The fluid should be right to the top. If not, you can top it up, engine running, with 50/50 antifreeze/water mix till it's full to the top.

If you see bubbles, as in lots, it may be a blown head gasket, blowing into the cooling jacket. If you keep losing fluid, you may have a problem elsewhere, like a blown headgasket into a cylinder. If so, the spark plug in that hole will look like brand new, washed clean.

Be careful with this, but it does work. Good luck.