Hi All, I have a sbc 350 in my 40 Ford, This time of year it doesn't get used every day and I noticed that it was skipping a little when it was first started but it would smooth out in a minute or so. Then I noticed thet the overflow tank on the radiator was empty. So, I go to remove the radiator cap and the thing pukes coolant out of the filler. Now remember, the engine is basically cold... started and driven maybe 40 feet. I did put a pressure tester on the cooling system and it won't hold pressure. Crankcase oil is clean, no chocolate milkshake going on. Plenty of steam coming out of both exhaust pipes. It all points to a bad head gasket, I've never had a SBC blow a head gasket before. What do you guys think?
Not a normal failure pattern on a smallblock Chev. Check plugs for indications.......also, lots of folks have air hose with spark plug threads that make a great test. Screw into spark plug hole.....put some air pressure in.....watch for bubbles in full radiator with cap off
Could be leaking coolant into a cylinder when it sits cold. Maybe pull all the plugs, let it sit overnight and crank it see if any coolant comes out. Maybe even put pressure on it overnight. You can also get a head gasket tester that checks for combustion gases when running in the coolant. Of course it could just be you have a coolant leak elsewhere and a bad plug or something. I wouldn’t condemn the head gasket just yet.
Like said above, head gasket failure isn't common on SBC but head castings from the 70s and 80s are bad about cracking through the exhaust seats to the water jackets.
Unless you see coolant leaking externally its time to pull a head and see whats going on You have steam coming out the pipes and its using coolant and overflowing and puckeing out the radiator when running cold . no oil contamination so its not a intake leak or something like that Pull the plugs and see if any are different looking first . SBC dont blow head gaskets often but it does happen . My 91 PU blew one once and it was into the cylinder, and we ran close to 10 gallons of water getting it home 40 miles . Wait to long and you might hydraulic it if you fill a cylinder while its centering. there is a tool that sucks air out of the radiator and runs it through a liquid and it turns color if there is combustion gases in the radiator. They do work I use it at work.
Be carefull with "overnight pressure". If cylinder decides to fill with coolant, you will end up with bigger problems.....twisted bent connecting rod when it tries to compress a cylinder full of coolant.
Thanks for the fast responses. BTW, I forgot to mention that I did use a combustion gas tester on the engine as well. No color change in the fluid. I will pull plugs soon and see what I find.
Is your rad cap lower than the rest of the cooling system and that’s why you’ve got an expansion tank?
Remove belt from water pump, remove thermostat housing and thermostat and fill on top. Start engine and you should see which side bubbles come.
On the old Vegas, we would take out one plug at a time and start it up. The offending cylinder(s) would put out a mist of water vapor. I had one in the shop around 1980, the cleanest Vega I had ever seen, the car was immaculate otherwise. We had a local shop that swapped Iron Dukes into them and also repaired the porous blocks somehow.
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