I recently bought a '68 convertible 400/4bbl. It has a very small (about teaspoon overnight) coolant leak that shows up in the depression in front end of valley pan, under the thermostat. (arrow in picture). The amount in this photo is from about a week of sitting. I originally figured it was the thermostat gasket but I replaced that and still leaks. I traced some chalk around the thermostat, coolant temp sensor, and blank plug on the crossover part of the intake manifold and no leak found. It seems to me it must be leaking where the crossover enters the heads and the liquid is settling in this depression.
Now leaks in a 50 year old car are not unusual BUT I am a veterinarian and antifreeze is highly toxic so I'd really like to NOT have to worry about killing someones cat when I stop by with the Firebird!
The car runs well and I have no plans to rebuild it but would it be possible (advisable?) to remove just the intake manifold and replace the gaskets? Is there some other location I should look for a leak? Any other suggestions? Stop leak seems like a bad idea.
Do you have a gasket between front cover and intake? You see the long thin bolt that brings front cover into intake? Chrome after market themo housing suck. Leakers...
Engine Test Stand Playlist: https://www.youtube.com/playlist?list=PLwoxyUwptUcdqEb-o2ArqyiUaHW0G_C88 restoring my 1968 Firebird 400 HO convertible (Firedawg) 1965 Pontiac Catalina Safari Wagon 389 TriPower (Catwagon) 1999 JD AWS LX Lawn tractor 17hp (my daily driver) 2006 Sequoia 2017 Murano (wife's car) 202? Electric car 203? 68 Firebird /w electric engine 2007 Bayliner 175 runabout /w 3.0L Mercuiser__________________________________________________________
Yes, never use stop leak. If you’ve ruled out the thermo housing and hoses it must be the intake. It’s fairly simple to remove and replace. Just takes some work and patience.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
Do you have a gasket between front cover and intake? You see the long thin bolt that brings front cover into intake? Chrome after market themo housing suck. Leakers...
I see some blue gasket between the water pump cover and the intake crossover.
Yeah the underside of that thermostat cover was nowhere near smooth. I figured it was the leak point for sure.
I am not exactly sure what year the engine is but it's not original to the car. I would imagine getting the right gasket kit would require that info? I have the engine number from the front passenger side but have struggled to see the casting date from the back side.
Had the sane problem with mine, leaking out the head/manifold gasket at the crossover. The gasket I used was almost like a black thick pressed felt. It adsorbed the coolant and wicked it out to the bottom of the manifold. I had a film of sealant around the port in the head and manifold but the coolant traveled through the middle of the gasket. Gasket worked well sealing the intake ports but coolant soaked right into the gasket and leaked. SCE intake gasket 128103, forget what I replaced it with but no leak now. Coolant also wicked to the intake bolt holes in the heads and corroded those.
Those aftermarket chrome thermostat housings always seem to leak. An aluminium one can be polished to a chrome like finish, if one wants it shinny, and it wont leak like the chrome ones. My brothers "69 Roadrunner had a Chinese made Holley housing that looked like it was part of a locomotive boiler. New gasket and a tube of sealant wasn't going to stop that from leaking, putting it on a belt sander to take the curvature off the mating surface helped.
Probly the seal between front cover and water x-over. Best way to install intakes is snug the tmg-cvr bolt to x-over 1st to get a good seal. Then intake to head. Separated x-ovrs and port matched all my intakes years ago to try different combos. Nice not having to remove x-over when tryn different manifold/carb combos...
X2 Region Warrior, on the torque sequence for the intake. I too separated the x-overs on two of my Edelbrocks. One, a 4bbl and one a dual quad. This made it fast and easy to go from dual to single 4bbl and back.
A related question: Is this car supposed to have an overflow bottle for hot coolant? My car does not and i've added too much coolant at times and it overflows when the engine is warmed up. Seems silly not to have one.
No overflow bottle, although many of us went with a aftermarket overflow container. In a perfect world your car will not overheat, your entire system has been rebuilt, you keep coolant level 2" below the top on the radiator and you wont loose any coolant.
Originally no overflow container. You didn’t fill the rad to the top. Most add an overflow. I use my windshield washer reservoir for coolant overflow. Works great with no mods needed
A coolant overflow recovery bottle may have first been installed to keep coolant off the driveway, but it will help your cooling system perform better as well. When the coolant heats up it expands and some will exit the rad. This isn't necessarily due to the cooling system overheating, but because the operational temperature of the coolant is hot. The system will perform better if there is no air in it. The way to keep air out is to use a recovery bottle.
I know someone is going to say they never had them back in the day, and it's correct to run with the coolant down a couple inches so it wont overflow when hot. That doesn't mean its not going to be more efficient with no air in the closed system.
It is silly not to have one, unless you have a 100 point correct show car, put one on somewhere. They can be hidden so it still looks stock or a shiny one can be added. I have a shiny one, not as good as a plastic one as you have to take the cap off to see the level. Plastic ones allow one to see the level without taking the cap off.
I have a buddy in Sugarland TX who works on a multi billion dollar LNG project. Heat exchangers is his specialty, tells me they have to be completely air free to transfer the most heat. Wont but a recovery bottle on his 69 because they didn't have them back then. Didn't have power brakes back in the day, or signal lights or heaters/air conditioning. May have noticed, this subject drives me nuts.
A coolant overflow recovery bottle may have first been installed to keep coolant off the driveway, but it will help your cooling system perform better as well. When the coolant heats up it expands and some will exit the rad. This isn't necessarily due to the cooling system overheating, but because the operational temperature of the coolant is hot. The system will perform better if there is no air in it. The way to keep air out is to use a recovery bottle.
I know someone is going to say they never had them back in the day, and it's correct to run with the coolant down a couple inches so it wont overflow when hot. That doesn't mean its not going to be more efficient with no air in the closed system.
It is silly not to have one, unless you have a 100 point correct show car, put one on somewhere. They can be hidden so it still looks stock or a shiny one can be added. I have a shiny one, not as good as a plastic one as you have to take the cap off to see the level. Plastic ones allow one to see the level without taking the cap off.
I have a buddy in Sugarland TX who works on a multi billion dollar LNG project. Heat exchangers is his specialty, tells me they have to be completely air free to transfer the most heat. Wont but a recovery bottle on his 69 because they didn't have them back then. Didn't have power brakes back in the day, or signal lights or heaters/air conditioning. May have noticed, this subject drives me nuts.
x2
No brainer...every car has one now. A '72 heat recovery tank works well and can be hidden better than the after market. The tank allows the expansion of the antifreeze and burps out the excess compressed air. When the engine cools the antifreeze goes back in the rad from the tank therefore no antifreeze loss.
I used a Canton racing products aluminum recovery can and Stant 16 lb. cap. Cap has both upper and lower seals. Everything is new. Overflow from radiator is plumbed to the bottom of the tank. Tank is vented via an overflow port at the top of the tank. Tank also comes with a clear sight glass style tube. If I top off the radiator cold I don’t push any coolant into the tank. System seems to hold pressure. Is it possible cap is bad or rated for too much pressure?
15 pound cap is stock pressure. I run one about half that much. A high pressure cap will let the coolant heat up to above 212F without boiling, but it also puts a lot of pressure on the whole system, rad, cap, hoses, head and crossover gaskets, pump and seals etc. My car runs at below 190F I don't need to put more pressure in the system.
Your cap may be bad but if it didn't let something out, fluid or air, once it got hot it could cause trouble. Maybe the system had some air pockets and the rad cap burped out the air, then when it cooled off drew the air back in. It's common to put some fluid into the tank when it is cold, 1/4-1/3 full, that way if some air was drained out to the tank it would be replaced with coolant. If you keep putting coolant into the tank and the level keeps dropping, you may have a leak elsewhere. Try another cap just in case that one's kaputski
That's a nice looking tank, could pass for a stock item. You still have your battery in the stock location? What's with the hole in the fender-rad support bar, have something bolted there?
It’s a Canton Racing Products 2 qt. Tank # 80-201, powder coated satin black. Yes, battery is in the trunk. Coolant overflow tank and electric vacuum pump for the brake booster reside where the battery used to be. I’ve owned the car since ‘79. That hole in the fender brace has always been there. I thought GM installed it, guess not. Lol.
I think the system is sound. Excellent point about boiling point. I hadn’t thought of that. I’ll try a new, lower pressure cap and see what happens.
Maybe GM did put it there, mine doesn't have one but could have been made by Joe Blow brace manufacturers. One thing about my not having a brake booster, I don't have to worry about vacuum levels, just press the pedal harder. The few times I've had to make a panic stop I was amazed at how much force I put on the pedal. It's kind of proportional to the size and distance of the truck that blows through a stop sign in front of you, the larger and closer the truck, the more force on the pedal. Old school ABS.
Not quite Flintstone brakes, I have '69-up single piston GM discs on the front. Still have the manual drum/drum master cylinder, I rebuilt it a couple winters ago and it works well. Just had to make sure there was a residual pressure valve in the rear brake's port and no valve in the front brake's port.
I looked up the Canton recovery tanks. I'm going to measure and see if I can replace the one I have with a canton. Mine doesn't have enough volume. The rad will fill the tank when hot then suck it all back into the rad when it cools. Tank is empty when cold and I have to still take off the rad cap to check the level. Always right up.to the rim and I spill a couple drops off the cap onto the paint or chrome.