ok i have a 302 out of a 74 maverick bored 60 over (yeah i know its too much, i didnt build it) its got a cam and 351 heads. alumunim radiator with a shroud and big fan. so i drove her to austin from ft worth no issues, temp stays at 180. got a little hot in traffic in austin and drove back fine. Now since ive been back it has started spraying water out of the overflow tube on the radiator. I replaced the thermostat with a 160 degree and put a new 20lb radiator cap on. what could cause this? im never getting over 200 degrees on the gauge and ive checked the sending unit and its working fine. so why in the hell am i spraying water out now. i have no water in the oil either.
You might want to have the heads checked as well; I had the same kind of thing with my Suburban and there was a cracked head.
.060 isn't too bad on a 302 in my opinion. On to the question: 20 lb cap seems excessive, but are you sure you're not just over full? After all, the overflow is there for a reason, water expands as it heats up.
Compression test, and cooling system pressure test, combustion gas in cooling system. That will take about an hour for both and give you proof one way or the other. Hope its just a head gasket and not a 60 over problem. You could also run the engine with the cap off and look for bubbles, if its not a very bad leak ithat might not be easy to spot.
Does the cooling system have a puke can on it aka coolant recovery can? If it doesn't make sure that coolant level is down a couple of inches in the top tank of the radiator cold so the coolant has room to expand. Then if that doesn't do it you are off to have the thing pressure tested and checked for combustion gasses in the cooling system as others suggested.
I just went through this on my 51 Ford Thanks to Wilson Rad shop. It was the wrong style Rad Cap. The early Ford cap neck is 1" deep and the new ones for pressuer caps is only 3/4" deep. A new style cap just does not seat and stop the water from pushing out the over flow. Just go check that first. There is a cap that will fix it or you can change the cap reciever to a late style. The Wizzard
READ THIS! Pull the plugs and check the color. The insulators should be tan to brown. If most are tan but one or two are snow white new looking then that's coolant leaking past a head gasket "cleaning" them. If that's ok then your over heating in traffic problem is retarded timing at idle/low RPM. Fix the retarded timing at low RPM/overheating in traffic problem by moving your vacuum advance source to manifold vacuum instead of timed or venturi vacuum. As to the puking coolant, put on a coolant recovery system like ALL cars have now. I run a 180º stat and a 7 lb recovery system style cap with a SBC and a '48 Chevy radiator and it will idle all day as cool as a field pump engine.
60 over is not too far, I just had the 351 I am building taken out to 60 over and when I questioned the race shop that is doing the machine work he told me not to worry at all. Don
.060 is a standard acceptable bore size on a 302,the biggest problem is builders installing 1 head gasket on upside down which does not let the water flow quick enough to cool the engine. It is a very common problem and the temp gradually climbs to a point of overflow from radiator. Dont worry about the .060 I have bored probably 100 blocks that size with no problems. Good luck
Let's get back to basics here. Does it have a coolant recovery tank (aka Puke Can, catch can)? If not then let's look at the next step. Back before cars had catch cans if you filled the radiator to the top, the first time it got fully up to temperature and then was shut off they would spit out some water. Then they would be fine. Basically they were seeking their own level. So after it puked, if you added more water, it would do it again, and so on. If you left it alone, it would be fine if everything else was working right. Usually the water would be down about an inch or so and that was fine. So, what have ya got?
it will dump coolant until its below the visible level, i always shut it off when i see more than several cups of water on the ground. ive blown head gaskets before and it always just overheats, this time though i can drive it for a good while and it stays under 180, but when i stop its bllowing water, and no i do not have a catch can. i did find that last week i drove it about 2 miles to a little local car show and i found that i had been leaking water leaving a trail for a while. the coolant does look like it may have a little oil sitting on top but the oil looks pretty good and not milky.
I have had radiators do the same thing and it just seems thay have to seek their own level. I don't put any more water in after it blows out and they have gotton no hotter and loose no more water.
Ding ding ding!!! Don't fill it up to the top, you need to leave room for expansion. I just fill my '66 Sub to the top of the tubes.
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