Ok, I have a 1987 3.9L Dakota with 68,000k, AT, Bad AC, 2wd, regular cab, short bed. I recently changed the water pump and all the front side gaskets, then the intake gasket blew. I changed that, it runs great. but the thermostat does not open until the temp needle gets half way up. Then it drops and runs fine. After replaceing the thermostat, The same thing happens.

I have read the post about "burping" and I have filled radiators before. Did I really get two bad thermostats in a row, with the same problem? or am I doing it wrong?

 

As long as the needle moves, and doesn't peg out, or go above, say, 3/4, you should be good.
I never had much of a problem with the cooling system on my truck, and really have never "burped" the system.
Usually, given the time, the system will de-air itself. At least that's what has seemed to happen to me.

 

I agree, I never had much problem either. I keep the overflow tank full and vacuum from the coolant (as it cools) should pull what you need back into the radiator system. I'm concerned now because this is why I changed the thermostat to begin with. It did get hot at first, this caused the intake gasket to blow.

The water pump, radiator, hoses and gaskets are all new. The only thing left is the fan.

 

You could put in a lower temp thermostat and it will not get as hot.....!!I have the lowest temp avail and barley gets 1/8 hot.....68K miles for a 87 pretty good.

 

This may be a stupid reply, but are you sure you put the stat in the right way, spring side towards the motor. As the spring gets hot it compresses which opens the thermostat. If it's put in upside down it will take lots more heat before it opens.

 

What temperature thermostats are you using? Should be 180. I would not recommend anything below that except for certain occasions. If it's not opening till it straight up, sounds like you might have a 195 stat in there.





Also, you've read the posts on burping, but did you burp the system?




.02

 

First off I told you wrong, it's a 1988 Dakota, not and 87.

I did make sure it was installed correctly. I referenced the Haynes manual, the way it was installed and the guy at Oreilly's.

As for the temperature, it is a 195. I've found all the way down to 160. This truck is fuel injected, not carb'd. so I don't know if a lower temp would throw-off the computer and keep it in the cold loop to much?

 

In reality the thermostat really doesn't have anything to do with how hot or cold a engine will run. It just determines when the coolant flows through the radiator. Prior to the stat opening the coolant just circulates through the block and heads. When the stat starts to open it floods the engine with cooler water, It seems that the thermostats you are getting open pretty quickly, which really isn't a problem. And you are right anything lower than 180 will keep the motor in cold loop longer then needed.
FYI
Most modern fuel injected vehicles are designed to run most efficiently at around 210F, with 190 being the bottom and 230 being the top end of that range. SO, you want to get the car/truck up to operating temp as quickly as possible. In colder northern climates that means a hotter thermostat. If you live in the south you can get away with a colder one.

 

Not so fast. Running a hotter thermostat will not warm the engine up faster. It will limit how hot it will get.

 

In the example I was giving, "getting a modern computer controlled engine up to operating temp", it will. A hotter thermostat will keep the coolant circulating in the block longer and at a higher temp before fully opening and letting the cold coolant from the radiator begin to circulate. Thus getting the engine to it's optimal running temp range faster.

A BAD EXAMPLE (LOL): If a 180 stat starts to open at 160 it will take longer for the engine to warm all of the coolant to 210 than it would with a 195 that starts to open at 185. It's all in when the extra coolant from the radiator is added into the system.