500 loses power when warm?

Discussion in 'Big Block Cadillacs' started by 76CoupeDe500, Jun 10, 2018.

  1. 76CoupeDe500

    76CoupeDe500 Member

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    Finally got back to work on my 500 swap and got it running. It will run 190 degrees all day idling in my driveway and around town. At that temp it will spin the tires all the way through second gear. It runs closer to 210 on the highway and when I get off the highway it turns into a dog. Won’t even spin the tires anymore. Part throttle driveability is not compromised.

    The only modifications are a 2115 intake, Holley 750 vac secondary, and headers. Factory 4 core BB radiator, brand new water pump, and 180 deg t-stat, Ford windstar electric fan-on at 190, off at 180.

    I’m not sure what temp range these things ran at from the factory , but I have a hard time believing they didn’t occasionally get to 210. Any and all help is appreciated.
     
  2. 76CoupeDe500

    76CoupeDe500 Member

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    Brain fart..... fan turns on at 200, off at 190. If it makes a difference.
     
  3. Ted in Olympia

    Ted in Olympia Active Member

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    I would have the fan turn on at 180 if possible. I had good luck with modern aluminum radiators and they seem to out perform factory copper every time.

    Not sure why you would loose power though, 210 is not too hot for these engines? Makes me kind of wondering if you are running lean?

    Ted
     
  4. 76CoupeDe500

    76CoupeDe500 Member

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    Ted-
    I thought it was lean too. I put in fresh plugs ran it at highway speed cut it off and pulled them. They showed slightly rich.

    I agree that an aluminum radiator would shed heat better, but it’s weird that it does fine around town?
     
  5. Cadillac Kid 1

    Cadillac Kid 1 Active Member

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    Three thoughts on your post. First of all do you have the correct Cadillac style thermostat with the bypass shut-off on the bottom?
    Secondly do you have a working vacuum advance?
    Thirdly, after chasing the "overheating" gremlin with bigger and bigger electric fans I talked to the engineers at Maradyne who conceded that NO electric fan would put out the airflow that a HD factory fan/clutch drive would.
    Greg Surfas
     
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  6. Darius

    Darius Well-Known Member

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    I like Ted's and Greg's thoughts. My first reaction was that 210* isn't what I'd consider hot, but that caused me to wonder about the accuracy of the gauge.
    All of the items mentioned are certainly worth checking (lean, thermostat, vacuum advance); but what caught my eye was the fact that part throttle drivability [was] not compromised. Additionally the power loss occurs after you've been on the highway. Could other components like the transmission or rear diff be causing a heat related drag on the engine? Just a thought.

    d
     
  7. 76CoupeDe500

    76CoupeDe500 Member

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    Cadillac kid-
    I checked vacuum advance operation with a hand pump and everything seemed to be operating correctly.

    Not sure about the t-stat. It’s a factory replacement from Napa. I’ll have to pull it out and check it. I may end up switching to a mechanical fan if this keeps being an issue.

    Darius-
    The rear ended is unchanged from before the swap, so we can probably rule that out. The trans is a th400 that runs through the factory cooler and an external cooler. I don’t have a trans temp gauge though, so I’m not sure exactly what temp it’s running at.
     
  8. bugzaper

    bugzaper Well-Known Member

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    Are you leaking any fluids i.e. on the ground into the oil.
    Is there foaming in the radiator.
    Does the oil look milky.
    I've seen cracked blocks / heads expand and leak when hot and than go back to normal when cold.
    Doesn't happen often but, can happen.
    Just a thought...
     
  9. danporterjr

    danporterjr New Member

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    had a boat where the fuel line to the carb was too close to the head/header and I believe the fuel was getting really hot maybe boiling before the carb. Kind of acted the same. Would detonation cause loss of power at WOT and does it happen more when the engine is hot? I'm not really good at troubleshooting just some first thoughts that come to mind.
     
  10. 76CoupeDe500

    76CoupeDe500 Member

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    Bug zapper-
    All the fluid levels are good and they don’t seems to be mixing at all. I will keep an eye on it though.

    Dan-
    You may be on to something there. The fuel line runs pretty close to the block/intake across the front of the engine. There’s no carb spacer either. I’ll try and re-route the line and dig up a spacer to rule that out.

    I appreciate everyone’s help. Hopefully I’ll get a second sometime this week to double check everyone’s suggestions and report back with what I find.
     
  11. 76CoupeDe500

    76CoupeDe500 Member

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    Update:

    Figured it out. It wanted more total timing. Between my excitement of getting the car running again and the laundry list of little things I needed to tweak, I forgot to check how much mechanical advance it was making. Turns out it was about 10 degrees. So with it set at 12 degrees initial I was only making 22 degrees total all in by 2200 rpm. I bumped it up to 34 degrees total all in by about 2300 and it runs at 190 all the time.

    Sometimes it’s the little things that escape us. Thanks everyone for all the suggestions.
     

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