Hey everyone,
My truck is a 91 Dakota 3.9 4wd. Currently my temperature gauge runs just right of the middle towards hot. When I bought it, it did this and I drove 70 miles home with no issues. I just went outside and replaced the T-stat and fresh antifreeze. I let it warm up and sure enough it went just right of the middle mark. I could tell the T-stat opened because the top hose got hot. It doesn't overheat. The heater inside feels nice and warm. Should I be concerned? It's 30 degrees outside and snowing. Also my radiator cap was cool to the touch. When I relieved the cap pressure it got hot.

 

You are probably ok. It might be worth it to install an aftermarket thermometer so you can read it in the cab, as opposed to just the C and H scale. My dash thermometer was bouncing all around like crazy before I blew out my heater core, now it stays pretty much at 12 oclock and my aftermarket gauge never reads above 180.

If you want to help out your truck a little bit, flush out your heater core, and swap out your 195 degree tstat for a 180 degree tstat. This may or may not be the best decision based on where you live and how cold it gets. Also make sure that your coolant is mixed properly with water.

For a final test, locate a thermometer, either a cooking thermometer or a digital touchless thermometer. Take off your rad cap and start your engine, let it warm up. Once you see the coolant running, it means your tstat just opened up and your truck is at operating temp. Take a reading, and then run back and look at your gauge in your dash. If your reading says somewhere near 190 degrees, but your dash is indicating 1 or 2 oclock towards the H, then you know your coolant system is probably working just fine, but your gauge or sending unit is a little miscalibrated. Not a big problem.

Let me know if any of that was confusing, and good luck!

 

Thanks for the info!

 

Mine runs really cool compared to yours. It almost never gets around the middle of the temp gauge.

 

Ok I got home from work today and the temp gauge was the way I've shown. So I pop the hood and check some things. The top radiator hose is hot and the bottom hose is ice cold???? Also the cap is cool to the touch. It is only 22 degrees outside so I'm limited as to what to do in the cold. I looks to have a fairly new water pump. Does anyone think the radiator could be clogged? Both heater hoses from the heater core where warm but not much heat inside the truck. If I take the cap off while the truck is running the radiator starts to overflow. I think I just answered my own question huh..........Sounds like my radiator is clogged and when it builds pressure it has no where to go. Any ideas??

 

Yeah looks like you are on the right track there, bottom hose on mine is lukewarm usually. When I went to the junkyard to pick up a new rad, I tested it by closing off all the holes and blowing into just one, checking for leaks. Then I blew through it, making sure it was not clogged. Something you can do is close off the upper hole where the rad cap connects, stick the nozzle of an air compressor in the coolant overflow hole and just blow through it, measur ehow much air comes out the bottom. If you think you are clogged there are products you can purchase to clean it out, but if it were me I would just replace it.

Oh, and if I was you I would probably not drive too much until the problem got addressed and fixed. A clogged rad is nothing compared to a blown head gasket.

 

My local NAPA ordered one for me this evening and it won't be in till Thursday. I think I'll go ahead and replace the water pump to be sure. It's parked for now. Freakin 16 degrees outside right now. Thanks for your help.

 

A wise investment. Good luck.

 

Ok today I replaced the radiator and water pump. I filled it up with the proper antifreeze and water mixture then fired it up. Well the temp shot almost to full hot then came back down some. I figured well that was just the T-stat opening up. I drove it down the road and it stayed about 3/4 just like it always has. Which I think it should be cooler. So I reached down and pulled the connector off of the temperature sensor in the intake. I looked inside the truck and the gauge dropped to 1/2 (perfect) but the check engine light came on. Could this be a bad sensor making it read hotter than it is? I've replaced the T-stat, water pump and radiator to date. The radiator was leaking prior. I don't know what else to do.

 

It could be a bad sensor as they do go bad, or miscalibrated gauge up on the dash. Did you perform the temperature test I described, involving taking an actual degrees measurement of the coolant and seeing how that corresponded to your dashboard thermometer? If 180 degrees reads at 3/4 on your dashboard, then things are alright.

I see you say that you have good heat coming from your heater, however if you have any doubts about that then you should definitely blow out or flush out your heater core. At one point mine was completely clogged up, and my needle on my dash fluctuated constantly between H and 3/4, even though the coolant read no hotter than 180. After flushing that out, not only do I get great heat, but my dash gauge warms up to directly 1/2 and doesn't fluctuate around, it just stays there, which I appreciate.

Did you replace the thermostat? Try and hunt down a 180 degree fail-open thermostat instead of the stock 195 degree option, it will let you run a little cooler and unless you live in Canada I don't think anybody needs to be running so hot. This type of tstat was readily available at my local Advance Auto.

Also, consider that the kind of crap that was clogging your rad was also being circulated through your entire cooling system. You may need to seriously flush the system, address tube elbows, nipples, and other linkage points, the heater core which is just a mini rad, thermostat housing and thermostat, etc. Your sensor could be coated in the same stuff, rust and old coolant, making it read incorrectly; take it out and clean it. To flush it well, I got myself a big 100 gallon bin, disconnected the upper rad hose from the rad, and pointed that at the bin. Then I started the truck and just let it circulate itself, adding water as needed to the rad, which trickled down the rad, entered the engine via the water pump, went through the engine and the heater core, passed through the tstat and finally exited through the upper rad hose, into the bin. I just about filled the entire bin before I got the water coming out to be clear, mine was really, really scummy. But, my truck is much happier, runs a lot cooler, I picked up a couple MPGs, my heater blasts super hot, and the dash needle is right where it should be. So give it a shot, who knows all you might have is a miscalibrated needle but doing all this can't hurt, and will onyl help the longevity of the life of your truck.