Running HOT, or not

[Sinjun]

Hey guys,
I purchased a 72 C20 2wd last fall, and have been working on it feverishly since. It's comming along, but have a question. Previous owner changed out the engine for a 283, and did a decent job. It appears to have a new radiator, and since I've had it, it does this strange thing... The temp guage will climb slowly all the way to it's hottest point, and after staying there a minute or so will climb back down again to about the quarter mark. I replaced the thermostat with a new one (185) and believe there was some air in the lines, and have been keeping an eye on the fluid level and filling it as needed. Any way, is this dangerous to allow the temp to peg on the high side, and let it come back down to what I believe is normal? What might be causing this?
Any ideas, thoughts, would be greatly appreciated. It's cold out there, and my motorcycles just went up for the winter, and would rather not find myself with an unexpected walk on a cold winters night.
Thanks!!!
-Chris

[pimperout]

could it possibly be ur fan clutch if you have one mabe its just kicking in at the wrong temp?? i dunno just an idea

[WorkinLonghorn]

If you really are running that hot then the radiator hoses will be very hard (and hot!) when squeezed.If not I would check the sending unit and the gauge,check the ground too.

[Sinjun]

Thanks guys for the quick responses. There is not fluid loss on the ground, or anywhere under the hood, oil looks good (no milkshake). To clarify a bit. This only happens after the truck has sat and is COLD Like in the morning or after work in the evening. I start her up no problem temperature starts to climb and goes all the way to the hottest point, and settles back down after a minute or so to it's normal operating temp.
-Chris

[Longhorn Man]

i would install an aftermarket guage, even just to check. You could remove it after you know you have/don't have an issue.
These guages were not too awsome 35 years ago, and it would make sence to figure they are worse now.

[WorkinLonghorn]

Me:

,check the ground too.

I shoulda said check that the gauge is properly grounded.Do any other gauges act at all weird?

[lilred67]

i have a mechanical temp gauge on my motor and it does the same thing.
it goes up to about 220-230 deg. right before the thermostat opens (165deg.thermo) and when the thermostat opens it settles out around 180 deg.. it acts like it's very sensitive to temp. hope this helps.

[Sinjun]

All my gauges seem to be working well... well except that speedo. which don't work at all, but thats mechanical not electrical. All lights work too. Also of note once the temp gauge goes back down to normal it pretty much stays right there hovering about 1/4 - 1/2 inch past the cold area. I also seem to hear a bit of rattling (water pump?) when the gauge is at it's hottest, but does go away when the needle comes back down toward normal temp.
-Chris

[john]

Do you have a coolant recovery system? Mine did the same thing after filling with coolant and before all of the air was purged. A coolant recovery will get about all the air out. Took about two days on mine then the guage read normal again.

[Sinjun]

Yes, I do have an overflow tank. It was empty a couple days back, and the radiator was quite low as well. I filled up the radiator,and then the recovery tank about half way yesterday morning before work. This morning the recovery tank was empty, but radiator looked pretty good. I'll check them both tomorrow morning again before I leave for work. Maybe I'll just keep topping it off for a day or two, and get all the air out. Does anyone think perhaps a cooler thermostat might be in order? It has a new 185 in there now.
-Chris

[stsalvage]

well I'm one for this question when that happens and if you don't want to blow a head gasket turn on the heater even on a 103 degree day you fry or the truck frys but you still fry while you wait for a tow truck or that long hot walk to the gastaion if the heater comes on and its cold you have a fulty guige if it pegs again turn on the heater if its still cold no worries but if its frying you out of the cab and it wont go down stop and turn off the engine

[Texasdeere]

Originally Posted by Longhorn Man

i would install an aftermarket guage, even just to check. You could remove it after you know you have/don't have an issue.
These guages were not too awsome 35 years ago, and it would make sence to figure they are worse now.

Most thermostats seem to initially open at a higher peak temp then settle down to a lower normal temp. But it shouldn't nearly peg the gauge when doing this. I run 180 degree t-stats in my older trucks.

[67sss]

radiator cap. change it and see what happens.

[Sinjun]

Well it's COLD here in New England, so the heater is turned on all the way. It blows pretty warm air, not hot and not very powerfully, but it's there and keeps the windshield defrosted, and the cab warmer than outdoors. On a 20 degree morning it takes between 5-10 minutes for the gauge needle to start climbing. Once it does, it will climb steadily till it pegs at hot, sits there for about a minute, and then backs down again to what I believe is a normal level (somewhere around 1/4 to 1/2 up the gauge. New radiator cap huh?
Excuse my ignorance but why? If so any particular type? Gives me hope though.
Thanks again guys!
-Chris

[67chevemall]

as long as it opens your fine. the old gauges are alot different to read.

[skokie]

Originally Posted by Sinjun

Well it's COLD here in New England, so the heater is turned on all the way. It blows pretty warm air, not hot and not very powerfully, but it's there and keeps the windshield defrosted, and the cab warmer than outdoors. On a 20 degree morning it takes between 5-10 minutes for the gauge needle to start climbing. Once it does, it will climb steadily till it pegs at hot, sits there for about a minute, and then backs down again to what I believe is a normal level (somewhere around 1/4 to 1/2 up the gauge. New radiator cap huh?
Excuse my ignorance but why? If so any particular type? Gives me hope though.
Thanks again guys!
-Chris

Sounds kinda like mine. It will go 2/3rds of the way to H then back all the way down to 1/3rd then settle right at about half.

[68speedalert]

Try this.

Drill an 1/8 hole in the base of the 'stat. If you have a small compression leak into the cooling system, an air pocket can settle under the stat and cause your problem. THe hole will let the pocket by pass the 'stat.

If that fixes it, I would get a 192 stat. A NAPA Superstat is an excellent one to buy. I say the 192, because it's good and cold were you are and you said the heater is not too hot anyway. Drill the hole it too.

[Sinjun]

Well, I put in a new aftermarket numbered temp gauge, and even though new thermostat was rated at 185 degrees it did not open even at 215 degrees. Put in another new thermosat rated at 180, and BAM that sucker opened up at about 185 degrees!!! and all seems to be fine now. I tooke the time while in the garage to clean out one HELL of a gerbils nest out of my heater duct work, and I've got good hot air blowing crazy through the vents now too! It was a nice warm ride around this evening for sure.
Psyched!
Thanks to everyone who took the time, and chimed in with ideas, and support. You guys are great.
Have a good night!!!
-Chris

[wheels67]

We love happy endings. Its always something obvious, isnt it.

[Brad]

Sounds like you figured it all out by now, but for future readers this is caused by air in the system and all one needs to do is open up the radiator cap after several drives and add coolant when low. This will help purge the air and level out the gauge reading. Of course make sure you don't open up the cap when the engine is hot, but instead when warm.

[Psycho71]

I was just going to say the same thing. I had a '98 chevy, and the water pump was weeping so it would loose water very slowly. The temp gauge would climb to max and then go back down periodically. It would scare the fudge out of me. Finally figured it all out. Air in the system would turn to steam, and superheat, making the gauge go ape! Changed the pump, filled with water, and filled again after driving, no problem anymore.

Glad to see you got it fixed though, and sounds like an easy enough fix. You gotta love those cheap parts that could ruin so many expensive ones, huh?

Jay

[Sinjun]

I've gotta say, I got LUCKY on this one! 2 days now. This (2nd) new thermostat is working great. The new temp gauge has not gone over 195 degrees.
Again I am psyched!!!
BTW a little thing I noticed with this new thermostat is that it had a little hole in its base with a small "floating" piece of what appeared to be copper wiggling around in it. Could this be a "built in" version of what 68speedalert was suggesting above??? Neither original t-sat nor the first new one I put in had this little addition. Hmmm curious.
-Chris

[FarmTruk]

Originally Posted by Sinjun

I've gotta say, I got LUCKY on this one! 2 days now. This (2nd) new thermostat is working great. The new temp gauge has not gone over 195 degrees.
Again I am psyched!!!
BTW a little thing I noticed with this new thermostat is that it had a little hole in its base with a small "floating" piece of what appeared to be copper wiggling around in it. Could this be a "built in" version of what 68speedalert was suggesting above??? Neither original t-sat nor the first new one I put in had this little addition. Hmmm curious.
-Chris

Congratulations...Sinjun, yer exactly correct on that little hole with the jiggly thingy in it. It allows steam from air pockets to escape out the top, thus "burping" the system.

That's interesting about the "defective" new thermostat you had originally. I always thought they were pretty much foolproof, never thinking that a new one would possibly be bad. Glad you found the problem.