I just purchased this truck two weeks ago. Everything ran fine for the first week, then it started to overheat.

It has a new water pump, I just replaced the thermostat ( its in correctly ) Had the rad flushed at a rad shop. Changed both Temp sending units on this truck. Also, I changed the fan clutch, as the fan was not moving very fast at all. I dont have any coolant leaks at all, my oil looks fine. My guage is showing at about 3/4 to the hot( its a sweep gauge ). I have read in a manual, that if this truck does not have a/c, it needs a straight fan, not a viscous one ? But Dodge does not sell them anymore, and I can not find one any were.....could this be the problem ? ?

 

Any chance you bought a cheapo thermostat from Autozone or the like? And have you kept checking the fluid level? You could have an air bubble. But I bet its a crappy thermostat.

 

I did buy one from a cheapo store. Fluid levels are all up, crazy good heat. When I had the rad and block flushed, we ensured there were no air bubbles left.

I will try changing the thermostat again. Have you ever heard of the solid spacer between the water pump and the fan blade. ? That is what the manual is calling for ?

 

I changed the thermostat with a 180 ' one. It idles just under half guage, and runs just over the half but under 3/4 mark. Is that ok ?

 

Since you live in Canada I would have put a 195 in.

 

It was working fine, now its going between half and 3/4 again. I took it on the hi way yesterday and it would go up to 3/4 and stay there at high way speeds, and it was about -15 last night.

Im wondering if it might be the water pump, it was just changed under a year ago by the previous owner ?

I dont have any coolant leaks......

any one have any ideas.

 

You may have a leak even if you cant see it! Sometimes it can be a pin hole size leak and it may only come out as steem or it could be on the front side of the raidator that you cant see. Have you checked your coolent level? Is it a little lower? Have you replaced the raid cap. These need to be replaced when you replace the thermostat. You should get one of those small hand pumps that puts your raid under pressure If it holds pressure for a certain amount of time then your raid is good. If it fails you have a leak. They are cheep like $5.

 

look and see if you got bubbles in your radiator with the engine running

if you do its probley a head gasket

 

coolant level has not gone down, i had the rad tested at a rad shop. I put a thermometer in the dash vent when the guage was between 1/2 and 3/4. The temp showed 120 '. Also, I havent seen any bubles at all but I havent ran it for a long time with the cap off, as the rad doesnt seem to be low. I will try that tommorow.
Im starting to suspect its the guage thats out...

 

Did you replace any of the hoses? If not, you might have a hose that's collapsing. Is the temp lower when at idle and higher when moving? If so, then your lower radiator hose (suction side) is collapsing. If the hoses feel soft and spongy when you sqeeze them, they need to be replaced.

Also make sure the fins on the radiator aren't blocked/clogged/bent.

In regards to your fan question in the first post, the factory service manual says the fan for a 3.9L without a/c is 17.5 inches in diameter, has 4 blades, and has a blade pitch of 1.5 inches (whatever that means). For a 3.9L with a/c, it's 18 inches, 7 blades, and a blade pitch of 2.4 inches. In both cases, it's a mechanical viscous drive fan.

It also could be the gauge being faulty. You could buy a cheap aftermarket one and see what it reads.

Good Luck,

Gerry