Overheating problem

[Eliwab22]

I’ve got a 98 1500 which has had a 99 5.9 swapped in (still running in the 5.2 computer) that has just started overheating. I just did a water pump when I put the engine in less than 1500 miles ago. Pretty much whenever I drive I need to have the heater on full blast and the engine temp will still climb. I was on the highway when the temp shot up, so I pulled off and was told to pull the thermostat because it’s a good chance that it was bad. It helped for a little bit by then the temps kept climbing. Any ideas on what could be wrong? I’ve tried flushing the radiator and block and it didn’t do much. I was thinking either it’s running lean with the 5.2 computer or the radiator is partially clogged.


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[DodgeTx]

could be radiator clogged, but 95% certain you need to purge the system or bump it.

Park truck on hill with radiator at highest point. Leave cap off it will bubble, fill it up with premixed antifreeze as it drops Run it to op temp with thermostat in place keep heater on full blast. may need to do more than once takes about 45-1 hour each time.

 

[Eliwab22]

could be radiator clogged, but 95% certain you need to purge the system or bump it.

Park truck on hill with radiator at highest point. Leave cap off it will bubble, fill it up with premixed antifreeze as it drops Run it to op temp with thermostat in place keep heater on full blast. may need to do more than once takes about 45-1 hour each time.

So I tried bleeding the system and found that only the top 3 inches of the radiator get hot. I assume that’s a clog of some kind?


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[cat199]

1. Did you remove the old thermostat and replace it with a new one? Or did you just leave it out?? If you leave the thermostat out it will overheat, there is passage at the bottom of the housing that as the thermostat opens to allow water to the radiator it blocks off thus water pump recirculation passage.

 

[ouch1011]

I had this issue when I replaced the engine in my Dakota (with a reman engine). I suspect there was some garbage in the reman engine that plugged the radiator, because the old engine performed just fine and didn't overheat at all (it just showed signs of really poor previous maintenance) , but the new engine would overheat very slowly on the freeway (or faster when climbing hills or driving hard). Replacing the radiator fixed it.

 

[Sam Davis]

Could be a plugged catalytic converter??

 

[EvilSpirit]

1. Did you remove the old thermostat and replace it with a new one? Or did you just leave it out?? If you leave the thermostat out it will overheat, there is passage at the bottom of the housing that as the thermostat opens to allow water to the radiator it blocks off thus water pump recirculation passage.

On 2nd gen Rams with Magnum engines, there is constant coolant flow through the heater core. There is also constant flow through a bypass port in the front of the intake to the water pump. When the thermostat opens, it allows coolant flow through the radiator, but it DOES NOT stop the flow of coolant through the bypass port. Since there is less restriction through the radiator than through the bypass port, the majority of the coolant flows through the radiator, but the bypass port continues to flow - there is nothing in the manifold or the t-stat that stops bypass flow.

 

[EvilSpirit]

So I tried bleeding the system and found that only the top 3 inches of the radiator get hot. I assume that’s a clog of some kind?


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Probably hit the nail on the head. Sounds like a clogged radiator. Since a crossflow rad fills at the top of one tank and empties from the bottom of the other, there usually are fairly consistent temps from the top to bottom rows - hot spots are usually caused by plugged cores.

You mentioned that you flushed the rad and block. I'm guessing that you didn't pull the rad to do so. It's hard to do a good back-flush with the rad in the truck. I like to pull the rad out, stand it up on end, and with the drivers side down, I give them a generous clean water flush. Still standing on end, I install the cap and plug the drivers side inlet and fill the rad with a 50/50 mix of white vinegar and water (HOT if possible) and let sit for about an hour. Another generous clean water flush from both directions and install. Also, make sure the fins for the rad and condenser aren't full of debris - good time for a quick rinse out.

Words of caution. 20 year old rads with plastic tanks are notorious for coolant seeps where the tanks are crimped to the aluminum cores, due to the hardening/shrinking of the sealing rings. I've had very limited success trying to tighten the crimps by squeezing the tabs. Also, sometimes the cleaning process dissolves crud that was sealing the tanks, creating a seeping issue. So with that said, you might end up trading a cooling issue for a leak issue.

While I usually don't change hard parts unless proven bad, replacing a 20 year old rad is usually not a bad investment - if the budget allows and the truck is a "keeper".

 

[Gr8bawana]

At less than $90 from Rockauto a new radiator to replace a 20 year old one just makes sense.

 

[Yeret]

At less than $90 from Rockauto a new radiator to replace a 20 year old one just makes sense.

Yes but plan on something screwing with you. When my radiator blew up, I nabbed a Murray from O'Reilly's. Everything went fine until I went to hook up the upper transmission cooler line. It didn't line up with the port in the new radiator. Turns out the upper tranny cooler entry port was slightly dropped compared to OEM. I had to bend the metal line to make it work and it worked with no problem but my point is that the new radiator wasn't quite as "drop and go" as it probably should have been.

 

[EvilSpirit]

At less than $90 from Rockauto a new radiator to replace a 20 year old one just makes sense.

I use Rock Auto parts a lot, but I don't always let the price dictate the final choice. While I have no problems cheaping out on parts for my V6 99 Dakota beater, I lean towards top shelf or OEM replacement parts for my 5.9 Ram that I tow a 4500lb trailer with, in 90+* heat and with the A/C on meat-locker. So, yeah, while money can be saved shopping R/A and other discount sources - rads and fuel pumps are items that are usually top shelf for me.