The Stovebolt Site Forums The Shop Area Engine Shop coolant usage

Hello all-
Here is one to ponder-
On my 3/4 ton- 216 with 4 speed, stock drivetrain-

Cooling system is currently stock radiator with all stock power plant-
When driving-
Like today, went about 450 miles round trip-
I used some coolant-

I know with the ) lbs cap the cooling system is open to atmosphere- what is the approximate evaporation rate for these trucks under normal driving conditions?

Normally I am running around town- nothing to far, maybe 15 minutes of constant running at a time- but like today and a few other times- Maybe I will see 100 miles between stops- cruising 45-50 mph.

I think total I added about 1.5 gallons. running prestone with water- I mix it myself about 50/50.

I figure the usage is about normal- but wanted to run it by you folks.

Truck ran fine otherwise- plan on a long trip next spring- maybe about 3 or 4000 miles total- mostly days like today. so it was good practice.

Sam I don't think you should be using any coolant. If you have had the head off recently I would go back in and re-torque it. If your not seeing any evidence of leakage from the outside there is a good chance your passing it through one of the cylinders. I had a similar problem after I did my valve job. I was being a smart ars and didn't re-torque the head. The plugs didn't show any problems but I was using quite a bit of coolant. When it started to show up by snot dripping out of the crankcase breather I gave in and re-torqued the head. Several thousand miles now with out adding a drop.
Denny Graham
Sandwich, IL

If everything is right, you shouldn't be losing any noticeable amount of coolant. A 50/50 mix should have a pretty high boiling. How full are you filling it. If you over fill them, they will burp out the amount you overfill them. GMC had a petcock about halfway up the top tank as a fill level. Other than that, I would suspect a leak into the combustion chamber as Denny explained.

Thanks for the response- Plugs are clean- no snot coming out- I will re-torque the headbolts and see what happens- I fill to about 2 inches below the opening. Using 50/50. and no snot coming out of the breather- So must be burning it off somewhere. I will let you know what happens.
Thanks again.

None of my trucks use coolant. It's been a few years since I've added any to any of them,
Scott

I had a cracked head on mine all last season and it didn't use near that amount of coolant. My GMC rad was designed to run with a pressure cap and without pressure it will lose coolant. I run a 7 lb cap and it doesn't lose any coolant. I think the tank of the radiator is not large enough to run without pressure. When I was burning some with the cracked head the only evidence was the color of the center insulator on that sparkplug. It also created a miss at low rpm.

Won't take but a few minutes to check it out Sam. It could just be leaking into the combustion chamber and not getting into the oil. In my case it was leaking into both areas. Since the fluid level was mentioned I might as well throw in my experience. Like Ken mentioned, I discovered real early on that if I topped it off it would just puked it out till it found a level that she was happy with. That level when cold is just above the cooling tubes maybe a 1/4" or so. When I check it warm she's about right up to the top. The volume of a few gallons of coolant increases a lot more than I thought it would with a delta T of 100°.


While we are talking about the "torqueing the head", I'd like to hear from some of you professional mechanic about your solution to torqueing the center bolt. How are you getting at it short of removing the rocker assembly? I can just barley get a crow-foot wrench in there and that's limited to just a few degrees of twist.
Denny Graham
Sandwich, IL

Denny,
on the gmc site they have a photo of an original tool to do that. It is a U shaped extention that goes around the rockers. What I do is undo one of the rocklers, pull up one rocker stud, slide the rocker over and use a socket/universal combo.

I'll have to go searching the GMC site for that tool. Sounds like it might be better than the crow foot if its a 12 point box end on the extension.
Denny G

Friday I re-torqued the head bolts in the proper fashion. They were a little loose- as in not 80ft lbs.
So got them to 80. Have put about 200 miles on since and no noticeable usage yet. So I think we might have a winner. Thanks all for the help.
Also drove the half ton about 150 miles this weekend. no usage on it either(noticeable)

For applying torque to the center stud I use a long extension with a crows foot on it- I found a somewhat long crows foot at harbor freight. I then slide it around the obstructions and then apply torque. works fine and does not contact anything.

Could you make that curved extension?
take a long extension- fix each end in something sturdy and heat the center while making sure that the ends stay straight- then curve the center section. It would take lots of heat and a decent hammer to tap the curve into it.
just an idea.