Pressure in the cooling system

[konstan]

Hey guys; haven't posted in a while since my escapades with the dash removal and a/c flap/distribution box replacement.

So I have this observation about my truck. The pressure in the upper radiator hose seems high. It does NOT build up when the engine is cold; not for several minutes. What I am concerned with, is that after the truck cools off and sits for a few hours, the pressure is still there. I do lose some coolant, but not too much - maybe a 1/2 gallon every 500-1000 miles.

After searching around, the only thing that I came up with is head gaskets, or worse (cracked heads or block).

No other symptoms. No coolant in oil. No oil or bubbles in the coolant. Runs smooth. Starts at the turn of a key when cold (I am relocating PMD right now). On hot days truck runs at 200F, on normal days it runs at 185F.

So, my question is this:

Can I still drive the truck? Assuming there is a (slow) HG leak, what are the risks? What's going to happen when it gets "worse"?

I figured I am going to pull the heads eventually, but I kind of wanted to drive the truck for a while first.

I don't do any heavy towing. Just go to my farm and back every weekend, about 100 highway miles each way.

Thank you all for reading this!

 

[bk95td]

Many have had good luck with the GM cooling tabs. It might be worth the try. Brooklyn Tow has kept his going on those for quite a while.
It might stall it for you long enough to really be ready to do it.Better to do it at your leisure than, have to do it now.

 

[Chief915]

The pressure in the upper radiator hose seems high. It does NOT build up when the engine is cold; not for several minutes. What I am concerned with, is that after the truck cools off and sits for a few hours, the pressure is still there. After searching around, the only thing that I came up with is head gaskets, or worse (cracked heads or block). No other symptoms. No coolant in oil. No oil or bubbles in the coolant. Runs smooth.

This all sounds pretty normal to me. The pressure staying in the hose after the truck sits for a few hours is actually a good sign in my opinion. If it's holding pressure in the system after it sits, that tells me there isn't a leak anywhere.... I could be wrong, but that is my gut feeling. Both of my personal 6.5's, as well as all my HMMWV's at work, hold pressure in the system while they are cooling down and don't lose any coolant.

I do lose some coolant, but not too much - maybe a 1/2 gallon every 500-1000 miles.

That is actually quite a bit to be losing, again my opinion. If you are losing that much, it has to be going somewhere. It will either go outside on the ground, into the oil (if you were dumping 1/2 gal of antifreeze into the oil every 500 miles you would definately know it), or going into the cylinder and getting burnt and put out the exhaust pipe, if it was burning 1/2 gal every 500 miles I would bet that you would have greyish white smoke while you were driving.

I don't want to insult your intelligence, but are you sure you aren't overfilling the coolant resivor? If so, it could be blowing te extra coolant out of the overflow hose once the system warms up and then "seems" low again later on. I doubt that's what's happening, I am sure you know better than that, but I had to throw it out there.

Can I still drive the truck? Assuming there is a (slow) HG leak, what are the risks? What's going to happen when it gets "worse"?

Well, assuming that it is a slow HG leak..... If you keep driving it.... several things could happen, this list is not all inclusive.

Best case scenerio... Try the cooling system tabs that BK recommended, you keep it full of coolant and keep checking the oil for contamination you may be able to drive it for quite a while yet without any problems. But, a little antifreeze in the oil will definately take life off the bearings.... how much life it takes off and how much life is left in them right now...hard to say.

Likely scenerio... you keep driving it and the disappearing coolant problem (assuming a slow HG leak) gets progressivly worse until it finally blows out completely all at once. Murphy's law says that will happen at the farthest point from help, at the worst possible time, and at the moment when you absolutely can't (money wise) afford for it to happen.

Worst case scenerio.... Again, assuming it is a slow HG leak, you keep driving it. The disappearing coolant eventually, maybe sooner maybe later, eats away at your bearings and causes one to spin, ruining the rod and crank in the process, and making your 6.5 a pile of scrap metal. You just went from a couple hundred dollar and couple day job of replacing head gaskets to whatever a new/replacement/known good 6.5 will cost you. Also, this will happen at the worst possible and least affordable time it possibly can.

Just my .02.

 

[orrum]

Ahhh HAH!!!!! I got my truck real cheap cause the guy had this exact problem and could find no leak in the radiator and he put all kinds of stop leak in it. It wound up the heads were ok and so was the gaskets. Mine ran at about 200 also. It runs hotter cause it cant build pressure due to the leak. The leak was in the bottom of the radiator sort of on the drivers side and was such a slow leak and intermitent due to the stop leak and it ran over towards the front wheel and when it finally dripped the drip actually hit the tire tread due to the air movement driving down the road so there was no evidence of the leak! I looked for several weeks and never found it. Then I had to haul two horses and the temp shot up to 235-240 and I pulled over to look under the hood and antifreeze was leaking off the edge of the driver side front fender. I loved the site of that leak!!!! Got a new radiator installed plus new radiator cap and antifreeze for $200 and aint looked back!!! Runs 165 or so when not towing now! U still might have a bad gasket or head or block but there is a chance its a tiny leak. The guy at the radiator shop said if u got a bad head or gasket to use bars leek cause its made from some kind of root and wont hurt anything. He said if u know for sure the head or block is bad and u r willing to chance the consequences he has seen miracles with the aluminum sealer in our blocks.

 

[konstan]

that tells me there isn't a leak anywhere....

I had that thought too, that there might be a positive indication in that...

I don't want to insult your intelligence, but are you sure you aren't overfilling the coolant resivor?

It is possible. I went through and fixed a lot of external coolant leaks on it. The quick coupling, the crossover, the return hoses to the overflow tank. While fixing all that, I may have gotten into the habit of just putting antifreeze in it without paying attention whether it was at the right mark.

Well, assuming that it is a slow HG leak..

its not that I am afraid of the head gasket job. I've done it before on the W123 Mercedes engines... I just want to avoid throwing parts at the problem before I know what is wrong. I think that maybe for now I will keep looking for bubbles and maybe try to find the kit for the coolant analysis.

Thanks you guys!

 

[orrum]

Oh yea my leak would not show at the radiator shop when he pumped it up, it sure showed when I heated her up with that trailer and two horses! Can I say again "IT MADE MY DAY TO SEE THAT ANTIFREEZE ON THE GROUND"!!!!

 

[konstan]

Oh yea my leak would not show at the radiator shop when he pumped it up, it sure showed when I heated her up with that trailer and two horses

Replaced the radiator just this April. The bottom hose fitting was cracked, no way it could be repaired.

 

[Michaeljp86]

My truck always had a lot of pressure on the radiator, even after sitting for weeks. It would have like 35psi, I changed the cap and that fixed the problem. Someone on this site or the other place told me to change the cap. I wasnt loosing any coolant though.

 

[WarWagon]

X2 on bad radiator caps.
Check the plastic tank for leaks. Hose clamps. Water pump weep hole.

A weak cap can blow off early and let the system boil off coolant or surge right after shutdown and dump coolant on the ground.

Just because the radiator is new doesn't let you rule it out. Things have a warranty... Check it again esp for install or shipping damage. Pull the trans oil dipstick as the in tank trans oil cooler could be leaking. Sample engine and trans oil to check for coolant.

 

[juddspaintballs]

Years ago I had a shop change the radiator in my s10 Blazer. They sent 3 radiators back to the dealership before they got one that didn't leak on a pressure test. New radiators can leak too!

 

[deejaaa]

i have some of the GM Stop Leak tabs if you want to try some, free of charge.

 

[Michaeljp86]

Years ago I had a shop change the radiator in my s10 Blazer. They sent 3 radiators back to the dealership before they got one that didn't leak on a pressure test. New radiators can leak too!

My dad had the same problem on his 89 2500 but they didnt leak until a few weeks later. The Shop said the factory had a recall on them. I guess they wasnt going to tell any customers unless it leaked.

 

[konstan]

i have some of the GM Stop Leak tabs if you want to try some, free of charge.

I got the tabs; will stick them in this weekend. I read somewhere that the upper radiator hose is the place to put them.

 

[Brooklyn Tow]

Crush them up to a powder (In the sealed package).....I used a "LFH"

I dumped them in the overflow tank and then was told to drive it for 30 min to 1 hr........then let it idle for 10-20 min, then put her to sleep for the night.

JMO and what I did.

 

[Chief915]

I used a "LFH"

Large Freaking Hammer ?

 

[Michaeljp86]

Large Freaking Hammer ?

No, large f***ing hammer

 

[konstan]

Today: 1) replaced the lift pump and added some creative circuitry that will run it when I turn the key instead of waiting till the oil pressure builds up 2) relocated PMD behind the license plate 3) put in the coolant tabs 4) drove it around for an hour and put it away

Next project: driver side rear end leaf spring; I think there is a bolt missing that causes the driver side rear sag. Like the bottom leaf is not "engaged" if you know what I mean.

 

[deejaaa]

Today: 1) replaced the lift pump and added some creative circuitry that will run it when I turn the key instead of waiting till the oil pressure builds up....................

gonna be a lot replies on that one, need to wire it back just in case of accident. want the lp to stop working if you lose oil pressure instead of pumping fuel into the fire.

 

[konstan]

gonna be a lot replies on that one, need to wire it back just in case of accident. want the lp to stop working if you lose oil pressure instead of pumping fuel into the fire.

Nah I wired it so that it (1) pumps when the glow plugs are on (2) when the oil pressure is present and (3) if I activate a switch under the hood, for priming. With two relays.

 

[Turbine Doc]

During your coolant consumption are you also keeping an eye on oil level ???

Summer 2009 we had a GTG in PA one member drove from Ohio "using water" so he kept on adding during the trip, what he didn't realize was it was going to crank case/pan and it & when we took pictures after dinner it looked like Exxon Valdez down side of his truck from blowing out turbo/CDR.

We did an emergency oil swap on spot sent him away with oil/coolant so he could change on way home 150 mile trip which got him home then met up a couple of weeks later his place & did a head gasket swap.

His was a bad case doesn't sound like yours as bad as his, I just wanted to give you heads up on where coolant may be going, if it is go water only until you get tabs in system as coolant can stick the rings.

BTW what coolant you running green or DEX, if green did you do good flush before swapping DEX & green aren't nice to each other