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Discussion Starter #1
Hey all,

I'm new here. Just joined because my truck is driving me nuts.
I have an 01 Dodge Ram Laramie, 5.9 engine, 4x4.
Shut the truck off one day, and it just didn't start the next morning. It was a damp, cold day. Engine would roll over, just wouldn't start.
Day 2, Cold day, but sun was out... engine fired right up, but check engine light was on. I had 4 codes on the obd II scanner.
First code was "Engine has been too cold, for too long"
Other 3 codes were pertaining to the O2 sensor in Bank 1.
Since the O2 sensor wouldn't give me a fail start, I figured it might be the Coolant Temp Sensor.
I replaced the Coolant Temp Sensor.
Now, the truck fires up and starts every time I hit the key.
But... Here is the kicker that I can't figure out... Now the Temp Gauge on the dash, just pegs hard into the overheating range. Way above 260.
Truck shows NO physical signs of overheating whatsoever.
I have replaced the radiator, water pump, and thermostat several months ago, and before this whole recent issue, the truck never showed signs of overheating. It was running just fine prior to shutting it off one day and it just not starting.
So, I figured it might be an air blockage from changing out the Coolant Temp Sensor, and I have tried to bleed the air from the system. Both radiator hoses get hot to the touch. Both lines coming from the heater core get hot to the touch. The coolant level goes down when ya have the cap off, and someone pushes on the gas pedal, which indicates to me that the thermostat is opening and closing just fine.
All I did, was change out the Coolant Temp Sensor, and now the gauge is pegging WAY hot... Please help, I'm baffled! Thanks in advance for your help, I'll try anything at this point. I'm lost.
 

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Maybe wire/connector issue, or new CTS is faulty.
 

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Discussion Starter #3
Hey, Key99

Thanks for the advice. Here is what I have done with the wiring....

I thought the same thing at first. So, I unplugged the CTS, and rotated the clip/harness 180 degrees, and put it back on... Restarted the truck...
Gauge went all the way into the cold range, and didn't move after over 15 minute in idle. Now keep in mind, just minutes before I did this, the gauge was pegged all the way over 260 and well into overheating range...
Next weird thing that happened was that it threw up a new engine code with the check engine light coming back on... Code was "Open ground in the CTS"
So, That kinda tells me that the wiring is okay, since I'm not getting a code when the harness is hooked up normally. And I am getting a code when I switch the harness 180 degrees.
I have also put a tester on the harness itself, and the parameters are within range.
 

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Where did you buy the sensor? I don't trust auto part store anymore when it come to sensors, ignition parts and emission parts. Quality control is gone. To me, it's worth the extra money at the dealer. Not saying that's what your problem is, but it's possible.
 

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Where did you buy the sensor? I don't trust auto part store anymore when it come to sensors, ignition parts and emission parts. Quality control is gone. To me, it's worth the extra money at the dealer. Not saying that's what your problem is, but it's possible.
Agreed, many many many have been bitten by chintzy quality sensors!
 

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OMG the quality out there! lets not start talking bout wheel hub bearings..
best thing you can do to protect yourself is to buy from a reputable store or buy only name brands you recognize. napa stores are not bad!
 

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Discussion Starter #7
I purchased the sensor at a local O'reily's Auto Parts. So... ya think it could be a bad sensor right out of the box? It's such a weird problem, and I guess if everything else checks out, what else could it be? It makes zero sense. I'll get another one, and try my luck with that. But while I'm thinking about it, do you all think it could be an airlock in the system somehow? Something that is just being a pig to bleed out?
 

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If there's air it's often heard in the cab (listen for gurgles from the htr core, more so when you hit/tap the gas); watch reservoir levels for proper/consistent operation (look every morning, then after its fully warmed up).
... If you suspect air, when engine is hot/normal and will then be shut off overnight, park with frt and pass side highest and tap the gas once or twice (gives air a chance to collect around the now higher rad neck area for discharge out the cap after the "heat soaked" engine is shut off), then shut it off. ... May take 3-5 days till res level stabilizes.
 

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Discussion Starter #9
Thanks. I'll definitely give this a try. Should I try to replace the CTS again? I mean, it's starting now since replacement the first time, and wasn't before replacing the CTS. Like I stated in earlier post, the truck doesn't really show signs of overheating... Just that the gauge now pins to the hot side (above 260) within 5 minutes of engine idle. I've let it idle with the rad cap off, and put my finger in the coolant... still cold... but gauge is pinned...
That's why I'm leaning toward it being airbound somehow when I replaced the CTS. But I have no idea. I'm stumped. Not even sure I should be driving it at this point. Thanks everyone for all your help on this. Keep it coming! LoL
 

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I bought a bad coil from napa one time, so I exchanged it and got another bad one. It makes it fun when you are trying to diagnose a problem. You said earlier that the coolant looked and felt like it was flowing through the system and didn't seem to have signs of overheating? If it was a vapor lock problem, I would think it wouldn't be flowing through the system. You also said it threw a code for a open ground? I would be looking more in the electric direction. Something I've done in the past to bleed air out of a system is, as the engine starts heating up, loosen the temp sensor a little at a time until you get some coolant seeping out past the threads. Any air that maybe trapped up in the top end of you engine will likely be sitting in there. Don't let the engine get HOT doing this. But again, it sounds electric to me. Did you reset the codes after putting new sensor in? What kind of condition is the is the connector/wires in? A temp sensor gun is a good investment too. Check what your temps are doing at the engine. Bad thermostat? It may be not be opening enough. I don't buy those at parts stores either.
 

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Discussion Starter #11
Hey Racefan41...

Yes, I have reset the codes. Still getting the o2 sensor codes, but nothing coming up for the CTS anymore. Originally I received 4 codes when the truck wouldn't start. The first code was "Truck has been too cold for too long". The rest were pertaining to the o2 sensor. So, since I have replaced the radiator, the rad cap, the thermostat, and water pump at an earlier time, maybe 5 months ago... And the o2 sensor wouldn't give me a "fail start", I figured I'd start in with the CTS. There were no over heating issues at this point.. Truck had been running fine. Shut it off one night after work, came out the next morning, rolled over but wouldn't start. I replaced the CTS. Now the truck starts, but the temp gauge flies over into the "HOT" side above 260 after just a few minutes of idle. Like I stated earlier, I took the rad cap off, and put my fingers right in the coolant... coolant still cold to the touch, but the gauge was pinned well over into the over heating range. No codes at this point. Just over heating issue. Truck purred along fine... Both hoses from the rad were hot, both hoses from the heater core were hot, and truck was throwing decent heat. So, for giggles I disconnected the wiring harness off the CTS, rotated it 180 degrees, and put it back on. Started the truck. Gauge was down into cool range, as if the truck hadn't run all night... and it instantly threw a code which was "open ground in the CTS." So, I figured that it sensed that I had messed with the wiring harness. Shut off the truck, cleared the code, and tested the wiring harness with a tester, which fell within spec of what it should be. Even did an Ohm test to check for continuity. Checked out fine. Hooked the harness back up properly to the CTS, and restarted the truck. No codes thrown up, just that the gauge pegged back into the over heating range. But again, truck shows zero signs of over heating. Not running rough, no steam flying out of the rad cap. Throws decent heat. Checked everything again with rad cap off, and someone stepping on the throttle for me, and coolant shows signs of thermostat working fine, cuz it drops down and kinda sucks into the rad when the engine is revved. I have no ideas where to go from here. It cured my no start problems, but now I'm really lost.
 

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Air at CTS would show cold gauge reading, and would bounce/rise when hot coolant flowed past it; that's been my experience anyway (with air due to low or loss of coolant).
... As racefan said, sounds electrical.
... DK if they're different, but older rams had 2 CTS, one for puter and another for gauge; perhaps they sold you the wrong one; again unsure if they're different, or if there's 3 different ones.
 

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Discussion Starter #13
This is a 2001. Would that fall into the category of having more than one CTS? The guy at the parts store only listed one. If everything checks at the harness, where do I continue for electrical issue? Not throwing any codes at this time, and if everything checks out at the harness to the CTS itself... where do I head next?
 

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Discussion Starter #15
No, no racefan41. I appreciate the help. Ya never know, I might just be overlooking something stupid lol. I've been known to do that from time to time. It's frustrating when ya fix one problem, and "create" another. All of your help is greatly appreciated. Hopefully, I have cleared up any questions ya might have had.
 

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What temp did the old one go up to when the engine was at operating temp? You can check the temp sensor with a meter if you know what resistance it should be at a certain temp. A thermistor is all the temp sensor is. It's possible it could be for another vehicle and just put in the wrong box. Look at the old one and see if you can google search the #'s on it. Might find who made the the oem one along with some info. If i recall the sensors used on the old blocks(60's-70's) had a temp stamped into them. Not sure if the new ones do. It pays to do your own research before you go and buy a part at the local parts store. Search the local stores sites and see what brands they sell, Stay away from house brands and junk brands. I would trust napa house brand stuff more than other stores because a lot of their stuff is made by doorman. Drill a small hole in the flat part of the t-stat, This will allow the air from being trapped in the motor.
 

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the temp gauge flies over into the "HOT" side above 260 after just a few minutes of idle.
I'm guessing bad or wrong CTS.

This is a 2001. Would that fall into the category of having more than one CTS? The guy at the parts store only listed one.
Category for 2 CTS is 97? and earlier; your parts guys listing is right, just 1 (but it could be faulty, or wrong part in the right box, orrrrr).
 

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Discussion Starter #19
Original operating temp was around 192 degrees F. To test the old CTS I place it hovering over a pot of water. As the water started to steam and boil I tested the terminals in the CTS. The resistance should have been starting to fluctuate and it did not. I did not see a stamp on the side of either the new, or the old CTS. But the 2 parts, both old and new looked identical in comparison when I removed the old one. Even right down to the thread count. I double checked it to make sure before putting it in. But it still could be faulty right out of the box. It was a Mopar part that I replaced the old CTS with. Not from a dealer, but an O'reily's parts store. But, if this CTS was bad out of the box... Wouldn't the truck fail to start still? That was what started this whole mess in the first place lol, the truck wouldn't start. Replaced the CTS, now it starts, but now gauges say the truck's overheating. Confused.
 

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I've never even heard of engine fail to start from a temp issue. New one to me. At least from an electric issue. If you got oil and antifreeze blowing out of the engine, maybe then.
 
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