Is The Problem The Thermostat In My Truck?

Discussion in 'Bad Dog Cafe' started by boneyguy, Sep 30, 2020.

  1. boneyguy

    boneyguy Doctor of Teleocity

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    My 2003 Dakota has developed a intermittent problem over the last month or so. The temperature gauge will climb right to the 'H" after the engine runs long enough for it to come up to temperature and an idiot light comes on and a ding-ding-ding alarm. The first few times it happened I turned on the interior heater and the fan to high and almost immediately the temp gauge dropped fairly quickly back to it's normal operating range. I'm actually stumped as to why the response was so quick as all I was attempting to do was draw some heat off the engine to help cool it. I wasn't expecting the dramatic and immediate response of the engine temp gauge. That still has me scratching my head.

    Recently it seems that just turning on the heater doesn't have the same effect. Yesterday I pulled over, turned off the engine and turned on the heater etc. again for maybe a minute or two but the temp wasn't dropping. After I started the engine again within a few moments the temp gauge began dropping and pretty quickly was at it's normal operating temp again.
    I haven't done anything about it because it doesn't happen that frequently and I'm not even driving every day these days.

    So, my thinking right from the start of this problem is that it's the thermostat. It's probably gotten sticky and worn and isn't opening up when it should some times. Is this an accurate or reasonable assumption. If it is I'll undertake the repair myself. I watched a YT vid and it's a fairly straightforward operation...I have all the tools.

    So, what do you say...thermostat or could this be indicative of another problem?
     
  2. Sparky2

    Sparky2 Friend of Leo's

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    Definitely the coolant thermostat.
    A 17 year old truck, and you got a very long life out of that stock thermostat.
    Be happy.

    Do you know where yours is located?

    On the 4.7-liter engine it is located at the end of the hose coming out of the radiator.

    On the 3.9-liter and 5.9-liter engines it is located at the top radiator hose where it goes into the engine.

    A MUCH easier change-out than my Subaru.
    THAT was a serious pain to change, that one.

    :(
     
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  3. boneyguy

    boneyguy Doctor of Teleocity

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    That's been my guess right from the start as well....the thermostat.

    I watched a vid for my truck on YT....so I know where to find it and what tools I'll need etc. It doesn't look like I have to be a contortionist with three arms to do the repair either. I guess I many have to drain some coolant out of that bottom hose though, right?

    EDIT: I think I was looking at the wrong Dakota engine....looks like mine's a 3.9L
     
    Last edited: Sep 30, 2020
  4. Ricky D.

    Ricky D. Doctor of Teleocity

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    Don't put it off. One of these days it's going to stick closed and disable the vehicle. Don't trust the temp gauge when it gets close to the red zone, it could be reading low. You'll kick yourself if you damage the motor by overheating.
     
  5. 985plowboy

    985plowboy Friend of Leo's

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    Sounds like you have it figured out and under control.
    I would go ahead and do it ASAP.
    It hasn’t left you on the side of the road yet.
    Why wait for it to happen.
     
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  6. MarkieMark

    MarkieMark Tele-Afflicted

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    I would never say definitely anything. But likely? Yes.

    I am assuming that you have checked the coolant level. Not just the reservour, but pull the cap (on a cool engine only)
    As I recall, some of those had the pressure cap on the upper hose.

    Assuming you are good there, Next step, yeah probably put a thermostat and gasket in it and re-evaluate. It is after all the least expensive/easiest thing to throw at the truck.
    Drain and replace the coolant. Its probably overdue. Again as I recall, there is a drain plug in the bottom of the radiator. If I recall correctly, drivers side. On those I think its a plastic plug, that turns 180 degrees to drain. Be aware they sometimes dont want to seal back up when tightened back up. The rubber o-ring is sometimes deteriorated/swollen and doesnt want to seal back up. Common replacement part.
    In my experience, the pressure cap is probably another item that is best just replaced at the same time. Often neglected part when servicing cooling systems.

    Going with the outside chance that is wrong and the thermostat doesnt fix it...
    The next step is the question-does the gauge go up sitting and idling or while driving down the road?
    Clues. Always need the clues.
     
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  7. Peegoo

    Peegoo Friend of Leo's

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    Changing a thermostat on most engines is about as simple as replacing a battery in most cars.

    The bottom of the radiator should have a small wingnut-lookin' petcock/valve, which simplifies removal of some of the coolant so you can work without spilling it.

    If the upper and lower radiator hoses and heater hoses are 10+ years old, now is the time to consider replacing those too.
     
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  8. Harry Styron

    Harry Styron Friend of Leo's Silver Supporter

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    Look at your dipstick and the inside of your oil filler cap. If either has a bunch of foamy gunk on it, you may have a leaky head gasket that is letting a little coolant into the crankcase, along with letting some compression into the cooling system that is interfering with the operation of the thermostat. I hope you just have a sticky thermostat.
     
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  9. EsquireOK

    EsquireOK Friend of Leo's

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  10. Deaf Eddie

    Deaf Eddie Friend of Leo's Silver Supporter

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    Here's another thought: my 1997 Ford F150's temp gauge pegged in the red, and the motor went into "limp home" mode. The next day, it started right up and ran fine. Took it in to the local shop, and after diagnosis they replaced the HEAT SENSORS (I guess there are two in that motor). No more problems. Now working on 360k miles...
     
  11. Viejo

    Viejo Tele-Afflicted Silver Supporter

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    I'm going to go against the grain here. My experience with thermostats is they either stick open or closed and stay that way. You may have clogged radiator tubes that don't allow enough coolant flow through the radiator. Turning on the heater is effectively adding a auxiliary radiator and increasing your cooling systems capacity. It sounds to me like your radiator is doing a marginal job of cooling the engine. In the old days they could unsolder the radiator tank and rod the core. In these days of plastic tanks and cheap cores about all you can do is replace the radiator
     
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  12. rangercaster

    rangercaster Poster Extraordinaire

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    The radiator could be shot, or a fan issue ...
     
  13. boneyguy

    boneyguy Doctor of Teleocity

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    What you are saying doesn't seem to jive with what's actually taking place though. The problem is only very intermittent. I can drive the truck for several days without any issue with the temp gauge in the normal range. Then I'll have a day where it will do as I have described and once the temp comes back down it remains at a normal temp for the rest of the drive. Also, I have twice, since this began, taken two 2-1/2 road trips (each way) on the highway without any issue. If it was a problem with the rad or blocked hoses I'd be inclined to think the issue would be much more consistently a problem, no?
     
  14. Lonn

    Lonn Friend of Leo's

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    Is the cooling fan coming on? Check to see if your radiator has a temp control valve at the bottom. My Acura was overheating last year and the problem was this little $20 valve. In a nutshell the computer wasn't getting the message that the water was hot so the cooling fans weren't coming on. One shop put in a new thermostat and replaced one of the fans (2 in this car). Charged me over $500. The car overheated on the way back to my house lol. Took it to another guy and he checked that valve immediately.....clogged.
     
  15. jvin248

    jvin248 Poster Extraordinaire

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    +1 replace the thermostat. They are inexpensive and generally easy to swap out. You'll need new coolant and a bucket under the engine when you take it apart. Youtube is a friend for getting the air out too.

    Also check your oil level and make sure you're not running low on that coolant.

    .
     
  16. stormsedge

    stormsedge Friend of Leo's Gold Supporter

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    Thermostat is a good place to start. Check you cooling fan also (as others have mentioned)...if electric, they do fail from time to time...those with fan clutches or solid mounts are less prone to failure.
     
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