500ci block overheating...
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500, 472, 425, 368 Discussion, 500ci block overheating... in Cadillac Engine Technical Discussion; I had just recently rebuilt a 500 block after I lost one to thrown connecting rods... Going into a '75 ...
  1. #1
    JvS
    JvS is offline Cadillac Owners Member
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    500ci block overheating...

    I had just recently rebuilt a 500 block after I lost one to thrown connecting rods... Going into a '75 Fleetwood Brougham. Anyway, after I finally got the thing dropped into the car, timing set, all the fun stuff, I noticed the engine would get extremely hot. I do know the motors ran hotter than other blocks, but this is incredible. After a trip across town, if I let the motor die it would not let me start it back up again until it is cooled off a bit. I replaced the water pump because part of it looked a little bent (pulley was wobbly), replaced the thermostat for good measure, and it still overheated. I am fairly certain water is circulating through the block. The only thing I can think of now is related to the gaskets, as there seemed to be a lot of passages on the block/heads that weren't cut into the gaskets (though the machine shops told me that it was normal). Again, this is a 0 mile engine, new pistons/crank/rods/etc... Any advice or help would be appreciated. Would hate to grenade a second engine in this car (first engine had actually thrown rods on two separate occasions, blaming the second one on a bad oil pickup). I tried the search function for this forum, no luck there. Thanks in advance.

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  3. #2
    Imprl59 is offline Cadillac Owners Fanatic
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    Re: 500ci block overheating...

    First thing I would do would be to stick a mechanical gauge on there short term to see if you really have an overheating problem or not. Have you had your radiator rodded out? If it is overheating and since you have already done the pump and thermostat I would look at the radiator next.

    Steve B.

  4. #3
    lux hauler is offline Cadillac Owners Connoisseur
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    Re: 500ci block overheating...

    Try advancing the timing......see if there's any change.

    Also, check the plugs......see if it looks like the engine's running lean.

  5. #4
    JvS
    JvS is offline Cadillac Owners Member
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    Re: 500ci block overheating...

    Pretty sure its overheating... After 15 minutes of running, the water boils through the cap and overflow for a good half hour . Would a 50/50 mix of coolant and water make a great difference? And will have radiator tested (or is there something I can do to check it?). Thanks for the replies, they're appreciated.

  6. #5
    lux hauler is offline Cadillac Owners Connoisseur
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    Re: 500ci block overheating...

    Make sure there's not an air lock some where and make sure you're running the correct pressure radiator cap.

  7. #6
    JvS
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    Re: 500ci block overheating...

    Alright, have it going into a shop to get radiator tested, going to get a temperature gauge for the water to verify it is indeed overheating. I pulled some plugs out, and they didn't look much like they did when I bought them (about 90 miles ago when I rebuild the first block). Not sure what they look like if the car is running lean, but how would I set the mixture a bit richer?

  8. #7
    Imprl59 is offline Cadillac Owners Fanatic
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    Re: 500ci block overheating...

    It does sound like it is overheating pretty bad. On any engine but especially on a fresh rebuild you are doing major damage every time it overheats.... It might keep going but bearings get damaged, pistons scuff up the cylinder walls, etc.. I wouldn't continue to run it until you figure out what the problem is and get it corrected.

    If the carb is correct there isn't anything that needs to be done to change the running mixture (you can change idle mixture but that isnt relevant to your problem). Carb could be clogged up causing it to run lean though. How about the timing? Are you sure that is set right?

    Steve B.

  9. #8
    lux hauler is offline Cadillac Owners Connoisseur
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    Re: 500ci block overheating...

    Check out the link below. Pretty good info.

    http://www.gtoalley.com/ttcool.html

    BTW.......the thermostat that you installed.......did it have the little cup type thing on the bottom side for the coolant bypass? If not, that could cause some water flow/cooling problems. Not that it, by itself, would cause the problems you're seeing but a few little things like that could.

  10. #9
    Sasquatch's Avatar
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    Re: 500ci block overheating...

    I know this sounds silly but check your vacuum advance on your distributor. If the timing isn't advancing properly during throttle up (this is the function of the vacuum advance) than that could cause the motor to run hot. I'd definetely check that radiator. Do you have AC? Check the fan clutch as well.:rolleyes2

  11. #10
    lux hauler is offline Cadillac Owners Connoisseur
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    Re: 500ci block overheating...

    Here's some more good info......

    http://www.oldcarsonly.com/page/page/776256.htm

  12. #11
    JTraik is offline Cadillac Owners Enthusiast
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    Re: 500ci block overheating...

    Maybe i can piggy back on this topic a little. I just replaced my timing chain and water pump on my 68 deville. I put a new thermostat in and a new sender (gauge wasnt working before i put this one in). I had the radiator checked...its fine.

    Im not exactly overheating but the car consistently runs at the 3/4 mark on the gauge, and in rainy weather it goes down to half mark. I drive the car everyday without problem, but i dont know if im just slowly ruining the engine by letting it get that hot. Also the car sometimes has a little initial struggle to start up but then goes fine....i had the absurd idea that the engine having gotten so hot was a making it a little tight in there...i dont know enough to say that though.

    I was told by my father that a hot engine like that shouldnt hinder starting and that the car is fine if it runs at that temp all the time. Do any of you have any opinions? Thanks!

  13. #12
    JvS
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    Re: 500ci block overheating...

    Thermostat had the little cup thing, I pulled cap off radiator and watched water flow from the upper hose into the radiator (so assuming there is atleast water flow). Tomorrow I'm taking radiator down to have it looked at, as today was transmission (flatbed to shop) since it didn't go into reverse or 3rd gear. I rechecked timing, and the vacuum advance did kick in. Spark plugs aren't covered in white (lean), and look normal. Could this be a part of the break-in? Bearing seats and all that? I'm running regular oil in it, and then switching to synthetic stuff after the 500mile break-in. Can't find the problem in timing or fuel... Even rebuilt carbeurator and replaced the fuel filter. Hoping (sad as that sounds) that the radiator is the problem, so I could put this worry behind. Thanks again for the replies and links, helped me a lot.

  14. #13
    lux hauler is offline Cadillac Owners Connoisseur
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    Re: 500ci block overheating...

    It's not part of the break in.

    What temp thermostat are you using? Make sure the cap is the right pressure cap for the engine........I believe you should have at least a 16# cap.

  15. #14
    Imprl59 is offline Cadillac Owners Fanatic
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    Re: 500ci block overheating...

    Quote Originally Posted by JTraik
    I was told by my father that a hot engine like that shouldnt hinder starting and that the car is fine if it runs at that temp all the time. Do any of you have any opinions? Thanks!
    A hot engine can hinder starting but so can advanced timing and a worn starter. A lot of the old high compression engiese suffered from slow cranking when hot. Double check the initial timing.

    The gauge being consistent is more important than where it is on the scale really. Gauge could be out of calibration or the new sending unit could be a little out. Gut feeling is that you are probably fine but if it were mine I would stick a mechanical temp gauge (that tells you the actual temp) on there for a few days to see what it is really doing. Anything over 220 and I start to worry.

    Steve B.

  16. #15
    Imprl59 is offline Cadillac Owners Fanatic
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    Re: 500ci block overheating...

    Quote Originally Posted by JvS
    Could this be a part of the break-in? Bearing seats and all that? I'm running regular oil in it, and then switching to synthetic stuff after the 500mile break-in.
    Not part of normal break in. Actually the overheating is causing much more damage because the engine hasn't broken in yet. Go ahead and change the oil now to another batch of dino juice and then change again as you were planning.

    Good luck on this. I hope its the radiator as well. Someone else here pointed out the fan clutch which was an excellent suggestion also make sure you have the "spring" in the lower radiator hose so that it doesn't collapse when it gets hot. Please let us know what happens with this.

    Steve B.

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