We live in St Maarten in the Caribbean. We have a 2008 Dakota pickup, V6, 3.7 engine. It had a blown head gasket. We removed the 2 cylinder heads and replaced the blown head gasket, and we placed a new water pump. We also placed a new thermostat. We ran the engine and it started overheating again. We removed the thermostat and filled it with 2.5 bottles of coolant. We ran the truck and after 10 minutes, it overheated again. The fan clutches are good. What could be the problem?

 

Make sure the thermostat is not in backwards. It can fit in either way but it matters which way it goes in.

And even though it's new, don't discount a bad thermostat. You can test it in pot of boiling water and see if it opens and closes.

 

A few thoughts i had about this.

If you ran the truck without the thermostat, a new water pump, and it was still overheating, that would suggest a lack of flow through the radiator.

Or it could be clogged coolant ports in the block. I've never replaced a head gasket on these trucks yet, but sometimes you can put the head gasket on wrong and it will block the coolant ports.

When a gasket blows it can start pulling coolant into the cylinder and flood the engine with coolant, or it can force oil and crud into the coolant system that can gum up the radiator. The last rebuild I did had a blown head gasket that had the block fill with coolant to the point it would barely turn over. The coolant reservoir also had a bunch of oil in it and the entire cooling system and engine basically had to be scrapped.

So I would check if you have flow through the radiator first. This can be easily done with a cheap infrared heat gun. Let it run for a few minutes to get warm, turn it off and check around to see if the heat is moving from the inlet hose to the outlet hose. Any cold areas are going to be where there is lack of flow through the radiator.

Grab the factory service manual (fsm) from the stickies at the top of the forum. There is a ton of useful info in there and diagnostic steps for troubleshooting.

You can check if the thermostat is bad by putting it in boiling water and see if it opens. And make sure the belt is on correctly so the pump is spinning the right direction, it's hard to mess that up, but not impossible.

If you get the issue sorted, I recommend the electric fan mod for these trucks. I had it on a 2011 3.7l and it made a noticeable difference when accelerating.