# Truck overheating.
**URL:** https://boards.straightdope.com/t/truck-overheating/670871
**Category:** Factual Questions
**Created:** [October 10, 2013, 1:37pm UTC](https://boards.straightdope.com/t/truck-overheating/670871 "2013-10-10T13:37:17Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@enipla](https://boards.straightdope.com/u/enipla)
#### Post date: [October 10, 2013, 1:37pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/1 "2013-10-10T13:37:17Z")
Just got a brand new plow installed on a ’04 Dodge1500. 5.7L Hemi. On the way back from the shop the truck overheated.
It was perhaps 45d F outside temp. It was flat ground.
Like most newer vehicles, it has an outside air temp display/gage. It read 108d F. Perhaps the new plow interfered with the airflow and caused the outside air temp gage to register so high.
So, my question - does the vehicles computer, which regulates fuel mixture use the same air temp gage that shows on the read out inside the cab?
My theory - 108 degree air would be less dense than 45 degree air. This would make the computer feed less fuel to the engine causing it run lean. Lean engines run hot. Is that right?
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### Author:  [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)
#### Post date: [October 10, 2013, 2:30pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/2 "2013-10-10T14:30:07Z")
> [@enipla](#):
>
> So, my question - does the vehicles computer, which regulates fuel mixture use the same air temp gage that shows on the read out inside the cab?
>
> My theory - 108 degree air would be less dense than 45 degree air. This would make the computer feed less fuel to the engine causing it run lean. Lean engines run hot. Is that right?
Nope, there’s a separate intake air temperature sensor actually in the intake (if your truck has one-- it’s not necessary in all fuel injection setups). The outside air reading in the cab is read by a sensor somewhere on the front of the truck, usually near the ground.
I’d bet that the problem is that your engine fan clutch isn’t engaging. It wasn’t a problem before because just the airflow through the radiator while you were driving was plenty to keep the engine cool, but now with the plow blocking that you need the fan to pull air through the radiator. That would also explain the high outside air temp reading-- the sensor is probably near the grille of the truck where normally only cold outside air passes over it, but now there’s either no airflow through the radiator or even airflow going the other direction so the front of the truck is getting hot.
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### Author:  [@enipla](https://boards.straightdope.com/u/enipla)
#### Post date: [October 10, 2013, 2:42pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/3 "2013-10-10T14:42:35Z")
> [@GreasyJack](#):
>
> Nope, there’s a separate intake air temperature sensor actually in the intake (if your truck has one-- it’s not necessary in all fuel injection setups). The outside air reading in the cab is read by a sensor somewhere on the front of the truck, usually near the ground.
>
> I’d bet that the problem is that your engine fan clutch isn’t engaging. It wasn’t a problem before because just the airflow through the radiator while you were driving was plenty to keep the engine cool, but now with the plow blocking that you need the fan to pull air through the radiator. That would also explain the high outside air temp reading-- the sensor is probably near the grille of the truck where normally only cold outside air passes over it, but now there’s either no airflow through the radiator or even airflow going the other direction so the front of the truck is getting hot.
Thanks. I was wondering about the fan clutch. I’ll start it and let it just idle. If the fan does not engage, and the truck gets hot I’ll know what the problem is.
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### Author:  [@Gary\_T](https://boards.straightdope.com/u/Gary_T)
#### Post date: [October 10, 2013, 3:02pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/4 "2013-10-10T15:02:27Z")
I think **GreasyJack’s** explanation is plausible, and assuming there aren’t coincidental causes for the two symptoms you’ve observed (engine overheating and higher outside temp reading) it’s almost certainly correct. Whether or not it’s a clutch-type fan, blocking/redirecting airflow from the radiator is a significant problem.
The only simple solution that comes to mind is adjusting the rest height of the plow to where it doesn’t prevent airflow through the radiator. If that’s not feasible, you will probably have to get a different brand/design of snowplow or forgo the plow altogether.
The outside air temp reading is just a convenience feature and is not a factor in engine fuel management. The computer uses multiple various inputs to calculate fuel delivery and if working properly will not run the engine lean.
> [@](#):
>
> I’ll start it and let it just idle. If the fan does not engage, and the truck gets hot I’ll know what the problem is.
It may not overheat sitting still and idling. The fan can probably pull air from around the plow easily enough in that situation. I fear that the airstream when the truck is moving at an appreciable speed is actively preventing airflow through the grill.
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### Author:  [@control-z](https://boards.straightdope.com/u/control-z)
#### Post date: [October 10, 2013, 3:20pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/5 "2013-10-10T15:20:18Z")
My bet is the people who installed your plow did something to mess up your cooling system; nicked a hose or something similar. Did you check your coolant level?
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### Author:  [@enipla](https://boards.straightdope.com/u/enipla)
#### Post date: [October 10, 2013, 3:35pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/6 "2013-10-10T15:35:17Z")
I called the shop that put the plow on and he has said mostly what Gary and Greasy have said.
There are 4 temp gages on the truck. The read out for outside air temp is not connected to fuel management.
It does have a clutch fan. And I’m going to be looking at that at a distance since I want to keep my fingers. If the engine starts to get hot, and the fan does not engage, I think I (we) have found the problem.
The truck does have AC and it looks to me like a transmission fluid cooler (stock) that is in front of the radiator, so that’s not helping with airflow. It’s a new truck to me, and I need to do some digging.
I’ll report what I find.
Thanks.
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### Author:  [@enipla](https://boards.straightdope.com/u/enipla)
#### Post date: [October 10, 2013, 3:38pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/7 "2013-10-10T15:38:22Z")
> [@control-z](#):
>
> My bet is the people who installed your plow did something to mess up your cooling system; nicked a hose or something similar. Did you check your coolant level?
Looked good last night, but hard to do when your on the road when it’s threating to boil over. The reserve tank had fluid.
That will be the first thing I do this morning before I fire him up.
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### Author:  [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)
#### Post date: [October 10, 2013, 4:25pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/8 "2013-10-10T16:25:11Z")
> [@enipla](#):
>
> The truck does have AC and it looks to me like a transmission fluid cooler (stock) that is in front of the radiator, so that’s not helping with airflow. It’s a new truck to me, and I need to do some digging.
On many vehicles, you could just turn the AC on, which will cause an auxiliary cooling fan to kick on. Unfortunately that particular trick doesn’t work on this truck because the AC condenser is off to the side instead of in front of the radiator.
One other thing to keep in mind is that even if the stock fan clutch is working, you may need to upgrade it to a heavier duty unit which will spin the fan faster at the cost of more drag on the engine. That might be a good idea anyways since this is just a 1/2 ton truck and once you get plowing you may find the stock cooling system isn’t completely up to the job.
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### Author:  [@Tully\_Mars](https://boards.straightdope.com/u/Tully_Mars)
#### Post date: [October 10, 2013, 4:25pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/9 "2013-10-10T16:25:52Z")
I’ll share an anecdote that may be helpful. My truck started running hotter early in the summer. It happened at the start of a 200 mile trip. I checked the coolant and the flow and found nothing obvious. I limped it home and then dropped it off at the mechanic. He used an infrared thermometer to determine that the bottom half of the radiator was clogged and not flowing. A new radiator solved the problem.
I don’t know much about plows, but wouldn’t it block the airflow on the lower half of the radiator?
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### Author:  [@enipla](https://boards.straightdope.com/u/enipla)
#### Post date: [October 10, 2013, 8:39pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/10 "2013-10-10T20:39:14Z")
> [@Tully\_Mars](#):
>
> I don’t know much about plows, but wouldn’t it block the airflow on the lower half of the radiator?
Yep it will. And that was my first thought. However, at least half the trucks up here have plows. And it’s a bit chilly year round at this altitude. I’m sure I or my shop would know that right off the bat.
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### Author:  [@enipla](https://boards.straightdope.com/u/enipla)
#### Post date: [October 10, 2013, 8:47pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/11 "2013-10-10T20:47:58Z")
Weirder and weirder,
So, I fire up the truck this morning and it is leaking radiator fluid. Looks like it’s out of the bottom of the rad. OK. It’s about a quart low. Not enough IMHO to cause a serious overheating of the engine when it’s only 45 degrees out.
I fill it up and the leak stops. Not so strange as I know that sometimes leaks plug themselves. Time for a pressure test though, and probably a new radiator.
I drove the truck into town for a test, and it overheated again. It does not seem to be leaking. It’s very odd. This is a used but from what I can tell not an abused truck at all, but it needs to go into passing gear to get up hills. My Pathfinder would leave this 5.7L hemi it in the dust.
I’m thinking that it may be something serious, or something as simple as the mechanical/spring radiator thermostat . I’m not sure it the vehicle even has one.
Is the engine too hot, or not getting hot enough. The heat to the cab warms up very fast. Hmm….
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### Author:  [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)
#### Post date: [October 10, 2013, 9:31pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/12 "2013-10-10T21:31:13Z")
You got some expert advice above for for some reason seem to be ignoring it. You can check your thermostat simply by seeing if your upper hose gets hot when the engine warms up. Once you feel flow through the thermostat a few minutes later your fan should kick on. These are all simple tests you can do in just minutes. Is your car going into passing gear or just kicking out of overdrive?
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### Author:  [@RedSwinglineOne](https://boards.straightdope.com/u/RedSwinglineOne)
#### Post date: [October 10, 2013, 10:26pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/13 "2013-10-10T22:26:23Z")
> [@enipla](#):
>
> Weirder and weirder,
> The heat to the cab warms up very fast. Hmm….
Is the radiator getting as hot as the temp gage would suggest? If not, it could be a head gasket. A blown head gasket can pump air into the water passages causing it to over heat very quickly (even though the water is cool), and the pressure can blow coolant out the overflow.
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### Author:  [@enipla](https://boards.straightdope.com/u/enipla)
#### Post date: [October 11, 2013, 12:01am UTC](https://boards.straightdope.com/t/truck-overheating/670871/14 "2013-10-11T00:01:18Z")
> [@HoneyBadgerDC](#):
>
> You got some expert advice above for for some reason seem to be ignoring it. You can check your thermostat simply by seeing if your upper hose gets hot when the engine warms up. Once you feel flow through the thermostat a few minutes later your fan should kick on. These are all simple tests you can do in just minutes. Is your car going into passing gear or just kicking out of overdrive?
What advice am I ignoring?
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### Author:  [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)
#### Post date: [October 11, 2013, 12:05am UTC](https://boards.straightdope.com/t/truck-overheating/670871/15 "2013-10-11T00:05:00Z")
> [@enipla](#):
>
> What advice am I ignoring?
I didn’t see where you checked the fan clutch, my apologies if I missed it.
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### Author:  [@enipla](https://boards.straightdope.com/u/enipla)
#### Post date: [October 11, 2013, 12:12am UTC](https://boards.straightdope.com/t/truck-overheating/670871/16 "2013-10-11T00:12:31Z")
> [@RedSwinglineOne](#):
>
> Is the radiator getting as hot as the temp gage would suggest? If not, it could be a head gasket. A blown head gasket can pump air into the water passages causing it to over heat very quickly (even though the water is cool), and the pressure can blow coolant out the overflow.
I would say yes. The rad is getting that hot. It’s kinda hard to tell though in the snow. The oil is a good dark brown.
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### Author:  [@enipla](https://boards.straightdope.com/u/enipla)
#### Post date: [October 11, 2013, 12:16am UTC](https://boards.straightdope.com/t/truck-overheating/670871/17 "2013-10-11T00:16:48Z")
> [@HoneyBadgerDC](#):
>
> I didn’t see where you checked the fan clutch, my apologies if I missed it.
I did check it. Maybe I did not report that. The fan is fine.
Been a long cold day.
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### Author:  [@Isilder](https://boards.straightdope.com/u/Isilder)
#### Post date: [October 11, 2013, 4:36am UTC](https://boards.straightdope.com/t/truck-overheating/670871/18 "2013-10-11T04:36:04Z")
Maybe the thermostat is stuck closed. That will cause the overheat. And the overheat causes the water to overflow ,as when the engine is off. gas pressure pushes water out.
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### Author:  [@enipla](https://boards.straightdope.com/u/enipla)
#### Post date: [October 11, 2013, 12:56pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/19 "2013-10-11T12:56:49Z")
> [@Isilder](#):
>
> Maybe the thermostat is stuck closed. That will cause the overheat. And the overheat causes the water to overflow ,as when the engine is off. gas pressure pushes water out.
I’m taking it back today to the shop that put the plow on. I hope it’s a simple as a thermostat
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### Author:  [@Rick](https://boards.straightdope.com/u/Rick)
#### Post date: [October 11, 2013, 1:34pm UTC](https://boards.straightdope.com/t/truck-overheating/670871/20 "2013-10-11T13:34:58Z")
This may sound a bit strange, but in dusty areas dust dirt and grit can block the air passengers in a radiator. That coupled with the disrupted airflow from the plow could be the source of you over heating.
Several minutes with a high pressure water hose from both the front and back side of the radiator will flush a good portion of the crud out.
Also if the truck was parked in a garage with a big sheddy dog you might have a blanket of dog hair decreasing the air flow.
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