Truck changes temp while cruising

[haysonj]

Took the truck out for its first long trip towing the boat. It seems to run 10 to 15 degrees hotter while cruising at 55 then it does in stop and go traffic. Could this be a timing problem maybe to much vac advance or to little. I have 36 degrees total at idle. Pulls in 34 degrees at 2500. Thanks for any help

[stonewall618]

im lost...

[Longhorn Man]

whats the temperature?
You sure it isn't caused by higher outside temps?
How much did the boat weaigh?
Any long hills you were climbing?

[haysonj]

Temp goes from 180 to 195 gets hottest when on flat ground that's why I thought it could be the vac advance pulling in to much advance at cruise I just checked the number on my advance can and it has a total advance at 10 to12 hg of 22 degrees that's way to much I have 12 degrees initial 21 degrees mechanical and 22 vac at cruise that's a total of 55 degrees. I need a different vac can. This Dist came out of a 1975 corvette so maybe it had a big cam in it.

[cdowns]

sounds like normal thermostat operation

[72swb_327stroker_?]

electric fan set-up?

[haysonj]

Originally Posted by 72swb_327stroker_?

electric fan set-up?

the fans come in at 180 and it can sit and idle all day and never go over 180 and you would think that going down the road it wouldnt need the fans. If I turn on the air conditioning the fans come on at 60 % and it would drop the temp by about 5 degrees also going up hill in second it would drop back to 180 or so. I'm sure it has something to do with timing

[LONGHAIR]

I just checked the number on my advance can and it has a total advance at 10 to12 hg of 22 degrees that's way to much I have 12 degrees initial 21 degrees mechanical and 22 vac at cruise that's a total of 55 degrees. I need a different vac can. This Dist came out of a 1975 corvette

I think you are a bit confused about the vacuum advance.....it gives you the most advance that it possibly can at idle, or when fully closing the throttle at speed. So you are only getting that if you are producing that much vacuum at cruise/part throttle. Do you have a vacuum guage that you can read while driving?
Several things effect the vacuum while driving:
the engine combination (ie cam, manifold,etc)
gear ratio
weight of vehicle and trailer
incline of hill
rate of acceleration
If you really are pulling that much vacuum, it could be causing some of the heat gain....but I don't see a problem with 195 while towing. Unless you are getting a ping/rattle/spark knock, I wouldn't worry about it.

[72swb_327stroker_?]

sounds normal to me

mine does the same at freeway speeds with fans at 100% duty

[Boog]

I'm pretty sure that 383 would hammer itself to death if it was getting 55* advance. Put an advance dial timing light on it and run the rpm up to 25 to 2800 rpm and read just what total advance it is getting.

[Longhorn Man]

I've never heard anyone complain about 195 degree temps before personally.

[haysonj]

Originally Posted by Boog

I'm pretty sure that 383 would hammer itself to death if it was getting 55* advance. Put an advance dial timing light on it and run the rpm up to 25 to 2800 rpm and read just what total advance it is getting.

Here is a very interesting article posted by Alaskan in the tech FAQ section (Timing 101) and this is where I got my information. Chevys like 36* total advance at WOT but at cruise speed on level ground run best at 52*. This should be read by anyone trying to tune a Chevy engine. http://www.hotrodders.com/forum/dist...1-a-59033.html

[haysonj]

Originally Posted by Longhorn Man

I've never heard anyone complain about 195 degree temps before personally.

I'm not really worried so much about the temp as I am the cause and of course the 8 MPG the truck is getting. My one ton with the same gears and a 350 motor gets 12 MPG towing the boat

[68gmsee]

I've had a similar experience on couple of my vehicles. One turned out to be a slight leak in the head gasket and the other a collapsing lower radiator hose.

On the head gasket leak, hot exhaust gases were forced into the water jacket causing a rise in temp. This happened mostly at higher speeds. Problem was when the engine cooled off, everything checked out. Hope this is not your case but it wouldn't hurt to do a leak test if everything else checks out.

Hose collapsing only happened under extreme load and heat conditions. I guess wouldn't hurt to replace if it looks like it's an old one with the wire coil inside...

[wzuke]

Are you using a clutch type engine fan? If so check to see if it is functioning properly.

[special-K]

Is this truck an automatic?It could be the trans/torque convertor heating things up pulling on the freeway due to minor (undetectable) slippage,inadequate cooling,or poor flow due to the need of a back-flush.Do you,by chance,run a trans temp guage?From my experience these trucks run steady low temp consistantly any way you run them.My GMC is doing pretty much the same thing.I`m suspecting my trans after going over the cooling system.It could be poor radiator flow.
On a truck I had I was experiencing climbing temps on the hiway.It`s a gradual climb all the way home.I could just make it to a certain exit before getting too high.Driving the old roads with curves,hills,and cool river valleys (letting off throttle and drifting) it could make it home.I ran it a couple weeks being really busy working sun-up to sun-down.I finally checked and it was the flex-fan all deteriorated to not much there from fatigued metal.So,the fan plays a big part in cooling,even at hiway speed with excellant air flow.
I hope this helps broaden your posibilities to look into.

[haysonj]

Truck has rebuilt turbo 400 trans with custom built torque converter for towing matched to the engine. Has duel electric fans and two trans oil coolers. Others suggested it could not possibly have 55* of advance at cruise but it did. This motor pulls 22 HG of vac at 55 miles per hour. I've changed Vac cans and it now is at 51* of advance at 2500 RPM I need to take it out again with the boat to see if it helped any. Thanks to everyone for the help.

[Boog]

That's some good info. I've been enlightened.

[68350]

a 4x4 will probably get 8 mpg, too, in case you're wondering. they definitely aren't gas savers!!