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Thread: Unusual warm up condition

  1. #1
    Registered Member Histoy56's Avatar
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    Unusual warm up condition

    Last year I purchased a '56 BelAir with a new 350 crate engine (290hp)with a chrome Edelbrock EPS intake. It has a Griffin high capacity aluminum radiator and the original 4 blade fan. Last year because of Covid, our club limited our activities to birthday and Senior Care facilities drive bys. In essence they were just slow parades. My engine didn't like those and had a tendency to run hot. I switched from a 195 thermostat to a 160 one, but that didn't help much. I then installed an electric fan in front of the radiator, which helped some. Over the winter I installed a 17", 6 blade fan so the engine should run cooler this summer. I do have an unusual warm up condition. I've installed 3 different 160 degree thermostats that have all intermittently given the same warm upcondition. When I install them I run them in my garage and watch the temp gauge to see when the stat opens. They all open around 160 degrees and hold that temp. When I drive around town, sometimes they open correctly, and sometimes they don't. When they don't, the temp goes to around 200 before the stat opens, and then the temp drops to 160 pretty quickly. I had the car on the highway a couple of weeks ago and the temp went to 230 before the start opened, then it cooled to 160 pretty quickly. That's when I bought the 3rd one, a never fail one. We had the car out to a cruise-in on Wed. and the stat worked fine. Today I took it to another cruise-in and I noticed that the temp went up to 195, so I opened the water control valve to the heater and the temp started dropping immediately. I closed it before we headed home, and I watched the temp and as soon as it hit 180, I opened the water control valve to the heater again, and the temp dropped immediately. The water flow from the heater enters the intake manifold right next to the thermostat housing. I'm beginning to think that there might be an air trap or something in that location that is causing my problem. I always drill a 1/8" hole on the thermostat, which I think should eliminate an air trap, so I'm confused. What am I missing?
    Last edited by Histoy56; 05-15-2021 at 07:59 AM.

  2. #2
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    Does your crate engine have Vortec heads? If so, does it have a bypass hose from the intake manifold to the water pump like you typically see on a big block? Vortec heads and blocks don't have the same internal bypass that all other SBC engines have. If there's no external bypass, you'll have the wild temperature swings during warmup that you report. This is due to an air bubble as you suspect, and your drilling the hole in the thermostat is the first step to a cure but it may not be enough.

  3. #3
    Registered Member Histoy56's Avatar
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    Thanks for your reply. This is GM's base 350 engine with cast iron heads, and there is no mention of Vortec heads in the description.

  4. #4
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    A couple years ago we installed one of those base motors in a 71 GMC it did not have vortec heads. It ran great unlike the 383 it replaced.

  5. #5
    Registered Member Histoy56's Avatar
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    The engine runs great, but the cam creates a manifold vacuum that's too low for the power brakes to work properly. I installed a hydro boost system to fix that problem.

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    You must have something wrong that Motor has a very mild cam that should idle 16/17 inches of vacuum at idle. It is sold as a stock replacement for 70/80s cars and trucks. My 74 Z28 with its much larger cam and my 67 Camaro with an even larger 30/30 Duntov both operate their OEM power brakes fine.

  7. #7
    Registered Member Histoy56's Avatar
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    Page 3 of the manual supplied with the engine states, "The 350/290 HP engine uses an aggressive flat tappet camshaft to achieve the level of performance for its intended usage". It has an 8.5 : 1 compression ratio. "Normal engine manifold vacuum for the 350/290 HP engine is 10 - 12" Hg at idle (650 - 750 rpm)". That's where mine runs. The engine runs surprisingly strong, but the vacuum was insufficient for good braking with the disc/drum power brakes. My wife drove the car 1 time and refused to drive it again until I improved them. We both enjoy driving our collector cars, and this '56 just wasn't safe that way. The brakes are excellent now with the hydro boost.

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    Did you have a chrome/gold about 7 or 8 inches in diameter from China. The 71 GMC 4x4 had great brakes with a stock booster.

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    Quote Originally Posted by markm View Post
    Did you have a chrome/gold about 7 or 8 inches in diameter from China. The 71 GMC 4x4 had great brakes with a stock booster.
    I just googled that cam we had a lesser crate motor, however your motor has the same Cam as a 73-74 Z28 .450/.460 lift 222 @.050 and everyone of those cars came with very good working power brakes. My sister and several girlfriend's have loved rowing gears in my low miles # match Z28. Every late 70s L-82 Corvette used that cam with power brakes too an well as 69 350hp 350 Vettes.

  10. #10
    Registered Member BamaNomad's Avatar
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    so perhaps the OP had a vacuum leak? or he had an inferior aftermarket booster?

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