Typically, if a motor overheats at slower speeds the fan is backwards or not up to snuff. If the motor overheats at higher speeds, the radiator is plugged or something is preventing coolant into the motor (like collapsed lower hose or plugged passages). At high speeds, the fan does essentially nothing to help cool since air pressure from the speed pushes it through the radiator.
With the antifreeze cool, remove the radiator cap and then let the motor warm up. Once the motor warms up and the thermostat opens you should see water flowing in the radiator. Is this the case?
Feel the lower radiator hose once the car is warmed up. Is it hot?
Since you installed a spring, it should not be collapsing so we can for the most part rule that part out.
When replacing the water pump, you didn't happen to mistakenly receive a reverse flow pump made for serpentine pulleys did you? This would prevent water from circulating through the motor and radiator.
I wonder if the vanes in the WP are as big as they should be? I've had cheapos with the impeller that was 1/2 the size of OEM, stupid ChiCom crap. Causes all sorts of funny transient overheating.
My other guess would be that the new radiator is being pumped full of crap...assuming it's not a hose collapsing.
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The squirrels in my head have spoken.
Cobra 5.0L & AOD swap, here we come.
Good point. If there was crap in the motor passages and he put in a new radiator, it could have pumped it into the radiator and plugged it up. I'd still like him to verify that coolant is actually running through the motor/radiator when warm.
Thanks for all the replies. I have a 7 blade flex fan, and the solid steel side is closest to the radiator. I drained about a gallon of coolant from the radiator and added water wetter and distilled water. No luck though, same story. I think its a flow problem, but there is no collapsing lower hose, I added a spring yesterday. The engine is a 78 302 from a Granada and Im using all the original 289 accessories, including the 65 water pump style. I cant see any obstruction in the radiator tubes. And once the car starts to overheat, it cant recover, even at a slight rev in neutral or at a slow steady speed. I have to shut it down and wait 10 or so minutes. But all thats happening in that time is heat soak, theres no way its cooling down in that time. Sure enough though, it'll recover once I start it back up. Im really getting baffled here...
I really appreciate the replys, keep em coming! I dont want to pull the plug on this!
Oh, and with the rad cap off and after it warms up to opetating temp, there is definite circulation visible in the upper tank. Im currently using a rebuilt original waterpump. I also have a new pump that i swapped out yesterday.
See if you can't rent a pressure tester from an Auto Zone, pump it up and see if it holds pressure. Maybe head gasket? Is your gage reading that you are over heating or is it just boiling over? Or is it doing both? Also check the dipstick for coolant or a clean spark plug. Sounds like you covered most every thing.
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Greg
1969 Mach1 "S" code 428 4-speed 3:89 gears,
31 spline posi "N" case, ported edelbrock heads,
full length headers, 292H Comp cam, 750 holley.
Born July 17, 1969
greg brings up a good point. How are you checking your coolant temps? Buy a cheapo mechanical water temp guage at Autozone and install it on the intake. You can remove your stock sender if that is the only port left. This will let us know exactly how hot it is running. The stock gauge/sender can be pretty unreliable, especially after sitting for awhile. Let us know the temps if you decide to go that route. Sometimes a faulty gauge can make you think the engine is hotter than what it is, even when feeling the motor or radiator.
Water circulating through a fresh radiator, good radiator cap seal, spring in the lower hose, new water pump, new thermostat, seven bladed fan oriented correctly...that's effectively a brand new cooling system.
I'd be worried about the water passages inside the engine at this point.
My thought was maybe it was a head gasket creating extra pressure in the cooling system and causing it to boil over and making it seem hotter than it really is. Also maybe the hot gases making the temp gage read hot. My thought is try to pressure check it and if it leaks buy a few cans of stop leak to get you home. I wouldn’t put them all in at once just one for now and see if it helps and just keep the others just in case.
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Greg
1969 Mach1 "S" code 428 4-speed 3:89 gears,
31 spline posi "N" case, ported edelbrock heads,
full length headers, 292H Comp cam, 750 holley.
Born July 17, 1969
I think you can buy a dye to put into the coolant system and a pair of goggles to see if there is combustion gases in the coolant system. This would likely eliminate a head gasket issue and I don't think the dye system is that expensive from Autozone.
I think you can buy a dye to put into the coolant system and a pair of goggles to see if there is combustion gases in the coolant system. This would likely eliminate a head gasket issue and I don't think the dye system is that expensive from Autozone.
Good to know! Sounds like a fun trip, I'm jealous... well except for the problems but it makes for a good story.
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Greg
1969 Mach1 "S" code 428 4-speed 3:89 gears,
31 spline posi "N" case, ported edelbrock heads,
full length headers, 292H Comp cam, 750 holley.
Born July 17, 1969
Replace the thermostat. If they sit for very long, they dry up or something? We bought a 68 that was in great condition and ran awesome. Had the fluids changed had a mechanic "check it all out". Took her on her first long highway trip (45miles), the thermostat was bad and the temp guage was not working properly. Long story short overheated her and then came the smoke in the tailpipe, then the ring job, then the new engine. A lot of work, time and money for $14 part.
Good luck and have a safe trip!
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