Z71-Guy

Hi Gang,

Well……..it’s my turn to have the dreaded “boiling coolant issue”

A little background, I ditched the TBI a while back and had an Eldebrock intake put on (with new intake gaskets put on at the same time) and a Holley 650 double pumper carburetor and a bunch of other high performance goodies like an aftermarket fuel pump that has enough pressure to feed the Holley carburetor correctly, a much better, more modern distributor, and a bunch of other electrical components to support the other systems since we ditched that horrible TBI setup.

She’s got a "true" dual exhaust system with 2 ½ inch Hooker headers & pipes, and she passes everything on the highway except for gas stations.

All of this work was done by a certified mechanic who specializes in old American muscle engines and the guy did an amazing job of putting everything together. He also spent months getting rid of all of the electrical gremlins. (of which there were dozens)

The transmission has been rebuilt, the rear end has been rebuilt, and all of the suspension components front & rear are only about a year and a half old. All of this work I'm describing has been done in the last two years so everything is still relatively new.

On to the problem……

About three months ago she overheated on me for the first time ever and the coolant reservoir was filled with a brown, muddy looking fluid. My first thought was that the head gasket had blown, but my mechanic checked all of that out and assured me that the head gaskets were fine. There’s no milky substance on the oil dipstick and no weird colors or smells coming from the exhaust. My mechanic explained to me that the "brown color" was caused by rust within the old radiator and that it's very common with these older systems.

I change the oil in this thing once every three thousand miles with that oil (for older blocks with tappets that has the Zinc) from Summit Racing and each time I change the oil, the oil coming out is almost as clean as the oil going in, and she hardly burns any oil at all every three thousand miles.

My mechanic told me that I needed a new radiator so he put a new one in, but not the one with the adapters for the transmission cooling lines because I ditched those a good while ago by converting the oil filter to a regular small block Chevy oil filter. I gained much more oil pressure by doing so, and eliminated the oil leak that everybody has with those horribly designed oil cooling lines. I don’t tow or carry anything so I’m not concerned.

She ran fine up until tonight………..I noticed the check gauge light was on and the temp needle was almost in the red. I pulled over and the coolant overflow tank was boiling like hell. Then I raised the red release lever on the radiator cap and the truck sounded like Satan gargling mouthwash.

I mean seriously, I backed up because I thought the whole damn thing was going to blow up!!!!!!!!

Once all of that madness stopped, I poured a bunch of coolant into the overflow tank and into the radiator and she took ¾ of a whole bottle of fluid into the radiator……..obviously she was very low because of a loss of coolant. Once that was done I drove her home which was about 7 miles away and she ran nice & cool

But like so many others with this same issue, I don’t have any fluid leaking anywhere, and no, I‘m absolutely certain that head gaskets are fine and that the intake system is solid with no leaks. One of the first things my mechanic did before he started all the work he did was to perform a compression check on the block and he gave it a clean bill of health.



Any & all thoughts are welcome…..

Gumby22

So your mechanic did a compression test before all this work was done, but no leak testing has been done since this problem started? Well, you may not want to hear it, but it needs to be leak tested again.

I’ve been a professional tech for 4 years (and a hobbyist for 20) and I’ve seen plenty of engines that need head gaskets but will still pass a compression test. Why? Because the head gasket is leaking but it’s not blown. Additionally, I’ve seen head gaskets that have been completely plugged with crud (or stop leak, if that’s been used before) and wouldn’t allow adequate coolant flow between the heads and block.

That said, there’s plenty of other possibilities besides the head gasket.

1) I’m not clear on your description of the new radiator (it may just be me but your description sounds contradictory to itself) - it sounds like you did an engine oil cooler delete. What about the transmission cooler? Because that could be the source of the dark/rusty color of the coolant.

2) The block may just need a thorough cooling system flush. A method I’ve used with success in the past is to drain the block and radiator, fill it with water and 1/2 bottle of CLR, drive to temp, then drain and repeat with water only. When the water starts coming out clean, the flush is complete and can be replaced with coolant.

3) Leak test the cooling system. Many parts stores will rent the testers - pressurize the system to the rating on the cap and watch it for 5 minutes - if it drops more than 1-2 psi, there’s a leak. Additionally, the radiator cap may be faulty and not maintaining the correct pressure - the testers usually have adapters for testing the cap as well.

4) Use Lisle tools leak tester kit #75500 or equivalent to check for the presence of exhaust gases in the cooling system. Follow the directions on the kit. We use it at work and have had very dependable results.

5) During all these modifications, was the serpentine belt routing changed? If so, it’s possible the water pump is spinning in reverse and it’s not circulating the coolant.

Z71-Guy

That is possible but like I said all of this work was done within a time span of about 2 years and the block currently has about 180.000

So while it is conceivable that there is some type of internal compression issue I highly doubt it given the strength of the motor, how well she runs, how strong he pulls, and how little to no oil is burned between the three thousand mile oil changes. It is a consideration however, and I'll more than likely have a "leak-down compression test done.

The head gaskets could be plugged with crud, I'll grant you that, but unfortunately the only way to know for sure is to just arbitrarily pull them "assuming" that they need to be replaced and that's quite an expensive assumption. I've also been wrenching on cars for close to 42 years and in all my years of ripping engines apart and restoring old cars I've never come across a block that had leaking or blown head gaskets where the oil dip stick was completely clean (the way mine is). If there was any milky residue at all on the dip stick I'd be more prone to go after replacing the head gaskets, but again, without having any other indications that an expensive assumption.

The old radiator (the complete radiator) was taken out of the car and a new radiator was put into the car. The only difference being that the new radiator does "not" have the side expansion section to accommodate cooling the engine oil. The transmission cooler was never touched, but that's a separate unit not tied into the radiator.

My mechanic performed a complete engine flush when he changed out the radiator and he did tell me that a lot of gunk came out, but that it was all flushed thoroughly before he installed the new radiator.

This was not done and it's worth having it done.....

There is a new serpentine belt on the truck, but I can assure you one million percent its on correctly spinning in the right direction, but good thought, very thorough.

Here's an update as of today.

After yesterday's fiasco I put close to 100 miles on her today and she ran great and didn't overheat. As a matter of fact she ran a pinch cooler, longer before she got up to her normal operating range which is about 195.

I attribute it to air in the system. When I unscrewed the cap on the coolant reservoir tank and raised the lever on the radiator cap yesterday she gurgled so loud & violently I really though the entire truck was going to blow up.......I took like ten steps back waiting for the damn thing to blow but after what seemed an eternity she calmed down.

I've seen a lot of post's on how these older trucks need to be "burped"....well she certainly burped yesterday. I also took the expansion tank off today and cleaned the hell out of it and replaced it with fresh coolant. It could have just been that the damn thing was never purged of air correctly when the new radiator went in.

I didn't change the thermostat but I did buy a 160 degree thermostat, and a 180 degree thermostat, and yes I drilled two small holes in each one about 180 degrees apart from each other, as I've seen tons of post's on how this "allegedly" helps with trapped air and water flow.

I currently have three bottles of coolant in the truck, along with the new thermostats waiting to go (if I need them) and all the tools I need to change this stuff on the side of the road. Marines are the ultimate Boy Scouts.....

So I'll keep my fingers crossed and do a "wait & see approach" for now as I've just sank a ton of money into this truck.

Thanks for the good advice and I'll definitely take you up on some of your suggestions.

oilcanhenry

I currently have three bottles of coolant in the truck, along with the new thermostats waiting to go (if I need them) and all the tools I need to change this stuff on the side of the road. Marines are the ultimate Boy Scouts.....

So I'll keep my fingers crossed and do a "wait & see approach" for now as I've just sank a ton of money into this truck.

Thanks for the good advice and I'll definitely take you up on some of your suggestions.

As a former Boy Scout myself, I would not compare that to the Marines at all. These days (I am not young) the Scouts use pellet guns, not .22LR bolt-action rifles as we did back in my youth. And that was only at a range with strict supervision by our Scoutmaster's. Beyond scouting, I had a great .22 LR rifle of my own.A Winchester Model 290 with Walnut furniture, I put hundreds of thousands of rounds down that rifle in my day, but she's kinda worn out now with an aluminum alloy receiver and a steel bolt.

Please keep us updated on your results, We very much like to see that we have helped someone to save some money and find a fix on their General Motors, vehicles.

Z71-Guy

Hi,

Sorry, I really should have come back in with an update, she's been great since I changed the hoses, cleaned out the overflow coolant reservoir, flushed everything and drilled 2 small holes into the thermostats as so many suggested.

I don't know how long the hoses had been on there but they were completely lined with rust and they were a large part of the problem.

I run a stock 195 degree thermostat during the winter months that I drilled 2 small holes into as everyone in here suggested to do, and I switch over to a 182 degree thermostat (also with 2 small holes drilled into it) during the summer months just to keep her away from the 200 degree range.

I'd love to just keep the 182 degree thermostat on permanently but during the winter months it keeps the engine way too cool, and the heat barely comes up on the really cold days.

I do have to periodically re-fill the overflow reservoir up every once in a blue moon during the summer months but I've accepted the fact that these older engines aren't as efficient as the more modern engines & cooling systems and there's no getting around having to re-fill it up every once in a blue moon.

She's not completely boiling all out the way she was doing before so it's a huge improvement. The heads are "not" blown and I don't have any water mixing with oil.

This old girl has close to 200.000 miles on her, and she runs like a sewing machine, really smooth and really strong.

My 1994 Acura Legend had me spoiled as I never had to touch it, and I think that's why I was so critical of this engine & cooling system, but it's fine, really.

Hope that helps.....