I just noticed tonight that when I'm sitting in the cab in drive (stopped) or neutral I can hear a single clunking sound every 30-60 seconds coming from the engine. I got out of the truck and popped the hood but couldn't hear that same clunk. Although I could hear a click which I'm assuming is the thermostat kicking on and off. Is this something I should be worried about? Its an 02 4.6L 8 cylinder 4x4 with 23k miles on it. Other than the engine running I had the heater turned on very low set to floor/def. ideas? I just started noticing this after driving about 12 miles at around 65mph and then pulling into parking lot and sitting idle (while i waited for my GF to drop off her car).

 

Once the truck is up to temp the thermostat will open and stay open. If it is defective it will allow the truck to overheat, causing pressure to build which will cause a clunking noise. since you had the defroster on I would suspect you heard the A/C compressor cycling on and off.

 

It's your A/C cycling every so many seconds. The A/C comes on in all positions except Panel and Floor - and Off of course. The thermostat is silent.

Fritz

 

Ahh the AC compressor runs even with just the heat on full bore? Anyone else notice theirs doing that? Its annoying.

 

I had a truck that did that, it was the ac clutch kicking on and off
it turned out it needed recharging.

 

I should notice the temp guage rising in that case right? I've never seen that happen its always dead center between hot and cold at most. I just bought this truck used a month ago and don't know much about it. I've got a trip coming up and was planning on taking it to the dealership to have them give it a once over since its still under warranty no skin off my butt. I'll bring up the AC and Thermostat as things to check in regards to the clunking.

 

I believe the temp "guage" is not a real temp guage. You'll see it rise as it warms up, then stay at one spot no matter how hot it gets. I believe when your engine begins to melt, an idiot light comes on.

Oil pressure is the same deal. A real guage will fluctuate with pressure differentials.

 

The temp Guage actually works. Been there done that. The 97-98 I believe actually use the temp comeing from the water jacket. The 99+ use the CHT sensor for a reading.

JMC

 

Besides, if it overheated the fail safe mode would come on, right? Dropping four cylinders to keep from self destructing? I've never had it happen, but I have heard it is VERY noticeable,,,,98

 

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It's your A/C cycling every so many seconds. The A/C comes on in all positions except Panel and Floor - and Off of course.
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I was told this once and never disproved it:
Even if you are in Defrost mode the A/C turns on to get the moisture out of the air. Even hot air. My thoughts are that most people call it an air conditioner but think of it as an air cooler, yes it does cool the air, but really it conditions the air and takes the moisture out of it using the condenser.

 

Nice truck chinook, but you may want to change the gallery link somewhat. It took me to the edit page for the gallery. I hit the add photos link, and it was going to let me add one.,,,98