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Howdy. I registered here to pick your brains about my truck. It's a 2001 Ram 1500 that I bought new in 2000. The other day the outside temperature was 100 degrees and I was sitting in traffic and I noticed the temp gauge was past 210 and rising. This was very hot for my truck, normally the gauge runs about 1 or 2 widths of the needle past the bottom line of 'normal' range (winter it's 1 width, in the summer it's 2). I'll attach a picture if I can figure out how.

I also noticed that the oil pressure was lower than usual, but both readings were still inside the brackets. I cranked up the heat and the temp leveled out. Then when I got moving again the oil pressure went back up and the temp dropped below 210 but was still way higher than usual. By now the sun had set so it was cooling off outside. When I got stopped and checked it out, the only thing I found wrong was that the radiator needed about 3 cups of water (the truck was not hot, I stopped and had dinner). The reservoir was full though, so I'm wondering why it didn't suck it from there. The cap was also on too tight. Whoever had it off last must have been a gorilla. I'm a big ole boy and I couldn't get it back on like how I found it.

I took it to my mechanic the next day. He said he found a fin that was bent that directs air to the radiator, but that's it and he thinks this is where the temp is supposed to be. I've got a stock 195 thermostat in it and always have had. Where you see the gauge in the picture is where it's been running for 520k miles. Somewhere I have a pic of the odometer when it got to 1k miles, if I find it I'll post it too. Right now, the needle is halfway between that lower bracket and 210. That's probably only a 10 - 20 degree shift, but it aint right.

Oh and for the record, 100 degrees may be the hottest day we've had this summer, but this truck has been in Texas all it's life. It's seen more days over 100 degrees than it's seen under 50.
Also of note, that check engine light you see in the picture is actually the computer complaining that the engine wasn't getting to temperature fast enough. BUT, that light was relatively new when the pic was taken. About a month ago I had the thermostat replaced and it was running at the same temp until last week.

So my specific questions,
1. Where do your temperature gauges run? My search of the itnerwebs tells me that my truck must be an outlier of some sort.
2. If I am an outlier, why would I be running so much cooler? Could my gauge be out of calibration?
3. Any thoughts on what could suddenly be making my truck run hotter? I have a very good mechanic, but he was busy and didn't look very hard this time because he thought the temp was right where it was supposed to be.
4. Last time I changed the oil I accidentally put in 5w-30 instead of 10w-30. Could that be causing the issue? I use mobile 1 full synthetic high mileage.

Thanks for your time.
 

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I would say your temp sensor is bad. Find a new mechanic also, he should have checked the codes before he did anything. Then he would have seen the code and then realize the temp sensor is not tell the pcm the correct temp. 210 is about where it should be at normal operating temp. I have 180 stat and it runs at 200.
 

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I would say your temp sensor is bad. Find a new mechanic also, he should have checked the codes before he did anything. Then he would have seen the code and then realize the temp sensor is not tell the pcm the correct temp. 210 is about where it should be at normal operating temp. I have 180 stat and it runs at 200.

You misunderstood me. There is no code right now. The code that was active when the picture was taken was fixed about a month ago with a new thermostat. The picture was taken a while back. Where is the temperature sensor? Is that in the instrument cluster? I will see if the computer reports the engine temp through the OBD port.
 

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I had the same issues a year or so ago,
I and I found out through trial and error
It was the fan clutch.
I couldn't believe it, because the fan was spinning up just fine to my eyes,
But under load while I was driving it,
Just wasn't spinning strong enough.
So I would suggest changing the fan clutch,
Its only around d a $30 item to try.

Good luck.
 

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the temp sensor is one of two on the intake manifold. right around the water thermos state neck, some have two sensors. right next to the water neck. on the intake.
 

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100º ambient temp outside and sitting traffic... I believe your temp is/was normal. You basically pushed everything to the limit so your rad might have purged some water out. When it cooled it should have sucked it from the reservoir I would think.

Oil pressure will drop hotter the oil. Reasoning would say when the engine is cold the oil pressure is always high. Once it gets hot the oil pressure drops.

Recently I ordered a Hayden Severe duty fan clutch for my 408. You might want to check you fan clutch. From my understanding when you shut the engine off and the fan keeps turning for a short while the clutch is wore out.

I bought a Griffin rad for my truck and with a 195º thermostat the temps sit at 200º-205º all the time regardless sitting in traffic or not. Bigger engine, hotter tune requires additional help in cooling...lol I have a aftermarket temp gauge so can read exactly what the temperatures are.
 

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a good new working viscous clutch fan will be louder and run at 100% till the fluids in the clutch relax and spin out, then the clutch will quiet down and run the fan at 30% till the arbor heat saturates and locks the fan up again.
 

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A bad temp sender will give wonky or no gauge readings. I've had vehicles where I've had to replace them multiple times. On an OBD2 vehicle a defective sender will cause other issues as the engine runs open loop or tries to compensate for a "ghost" condition. Your truck should not run that low. In my experience these PCM-driven gauges are usually pretty accurate and consistent, so there's no reason to assume an inaccurate gauge, unless, as you say, it's always run that low. With a capable scanner you can get the actual engine temperature while it's running and compare. A properly functioning vehicle will show 195-205 degrees as the normal operating temperature, and this is where it should be.
 

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I read this thread with interest because it describes what was happening to me with my 2001 Dodge Ram 1500/5.9. 250,000 miles on it.

Truck was running great, using a little oil, but not much. Temp normally about midway on the gauge. It started getting really hot really fast. I looked at the obvious first and decided it has to be a head gasket blowing into the water jacket somehow.

Bottom line: Since the truck has this many miles on it already, I didn't want to spend a lot of money pulling heads, etc. so I did some patching.

New radiator
water pump
fan clutch
thermostat

All these things had been subjected to extreme heat.

I put some block and head gasket sealer in, followed the directions and it seems to have worked so far. About 3000 miles so far, temp is good, no leaks, and the truck still runs great.

Before anyone starts throwing rocks at me for "rigging" something, I know it's a temporary fix. Spending $65 for that quart of snake oil may buy me another year or two on an 18 year old work truck. Money well spent already. In the mean time I have time to shop around for a newer one instead of having to take what I can find in a day.
 
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