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Hot Rods engine temperature

Discussion in 'The Hokey Ass Message Board' started by sic-nic, Dec 20, 2015.

  1. sic-nic
    Joined: Sep 27, 2009
    Posts: 212


    hi guys, looking for some help with an issue i have. i have a 1979 350 chevy engine in my '31 model A coupe and the temp gauge goes to around 205-210 degress and then drops like a rock to 185 which is the thermostat that is in it. i have flushed it and changed the thermostat twice and it still does this. once the gauge drops to 185 you can drive all day and it does'nt go up. once the engine cools it does all over again. the only thing i have not done is change out the temperature sending unit. i have VDO gauges in the car. any help would be greatly appreciated, sic.
  2. What are you using for a t stat. Some of the cheapos stick until they open the first time. I have been using a Mr. Gasket fast acting for a few years but I have also had good luck with a Moroso fast acting. They run about 11 bucks so its not like that are going to break the bank.

    The Stant stats are not as good as they used to be and you are way better off with an "expensive" racing stat.
  3. metlmunchr
    Joined: Jan 16, 2010
    Posts: 781


    You're picking up the temperature in the head which is going to heat up faster than the area around the manifold where the thermostat is located during warmup when there's no water flow thru the engine. Since it stabilizes after the warmup cycle, it really isn't a problem.
  4. i have two running hot rods , both have SBCs with identical intake manifolds , water necks and 180 degree thermostats . on my `28 it will go up to 180 and stay there . my `36 it will go up to 200 the first time you start it cold , then go down to 170 , then up to 180 and stay there. i have tried 4 different thermostats in the `36 and they all do the same....i can not figure it out , but since it doesn't really get to hot and it stabilizes at 180 i am not worried

    both cars have electric temp gauges with the senders in the intake manifold AND direct read mechanical gauges on the engine so i know it is not a bad gauge

  5. BJR
    Joined: Mar 11, 2005
    Posts: 7,243


    Try drilling a 1/8" hole in the edge of the stat to let any air or steam through. That may solve the issue.
    dana barlow and Hnstray like this.
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 50,252


    so, what's the problem? it doesn't sound like it's hurting anything.
    1927graham and henryj1951 like this.
  7. FrozenMerc
    Joined: Sep 4, 2009
    Posts: 2,776


    Like others of said. It is working perfectly. Sounds like the temp sensor is accurately reporting the temperature of the water where it is located. The water around the temp sensor heats up to 210 or so, by this point, the thermostat opens because it is now seeing 180 deg water, and the cold water that was in the rad rushes through the engine cooling the temp sensor down. Everything stabilizes at 185 or so. Please understand that the temp sensor only takes the water temperature at the location that it is installed, and they frankly don't react all that fast to temperature changes since most sensors are built into sizable chunks of brass and surrounded by coolant.

    With my '51 Ford F-1, the temp gauge with oscillate between 200 and 150 when cruising down the highways on cool or cold days. This is because the sensor is right behind the thermostat in the intake manifold and the radiator is efficient enough to drop the water temp to a point were the thermostat will close for a bit, the engine heats the water back up, and than the stat re-opens. This looks odd on the gauge, but everything is working exactly how it is supposed to.
  8. sic-nic
    Joined: Sep 27, 2009
    Posts: 212


    i have had the car on the road for almost 5 years and last summer is when this started happening. so i know that it may not be hurting anything it was strange that it started happening. thanks for all the input.
  9. Gas Giant
    Joined: May 14, 2008
    Posts: 402

    Gas Giant

    I had a T-stat do that in an SBC once. Would almost overheat the engine at first, but then it was fine until the engine cooled off. Went away when I swapped out thermostats, must have been sticking closed until there was enough pressure to pop it open.
  10. Bert Kollar
    Joined: Jan 10, 2007
    Posts: 1,081

    Bert Kollar

    Might be an air pocket. Try purging the cooling system
  11. dana barlow
    Joined: May 30, 2006
    Posts: 4,555

    dana barlow
    from Miami Fla.
    1. Y-blocks

    I always do that. Thats the right thing to do!,I'll add that after hole is drilled when replacing it,be sure that hole you drilled is at top when replaced
    . This both helps a better reading an when your filling with water you will not get air bubble,except if your top hose has big hump or your cap/fill is lower then it should be=things that should not be done anyway.
    INVISIBLEKID likes this.
  12. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,188

    from Kansas

    My 98 Sliverado did the same thing, right from the dealer when it was new. Seems that Chevy might have cut out the bypass cycle when warming up. Chevys are suppose to bypass thru a passage in the block that diverts some of the water back to the water pump. Perhaps this bypass is not working.
    I had a 51 GMC with a transplanted 235 that did this till I replaced the heater hoses and found one of the fittings for the hose was clogged with rust. Cleaned it and no problem. Heater core is the bypass in that case.
  13. sic-nic
    Joined: Sep 27, 2009
    Posts: 212


    i have purged the system twice. i am going to replace the sending unit and i will try the 1/8" hole in the thermostat. that hole, should it be drilled as close to the edge to where it sits on the housing? let me know i want to make sure it's done right. thanks again guys, sic
  14. squirrel
    Joined: Sep 23, 2004
    Posts: 50,252


    the hole would need to be somewhere that it's not going to be covered with the gasket, and not affect the opening mechanism. So, there are lots of places to put it. 1/8 might be a bit large, or maybe not, depends how much you drive when it's cold out.

    I really doubt the sending unit is causing any problems.
  15. miker98038
    Joined: Jan 24, 2011
    Posts: 679


    I had a 79 L-82 Vette motor that did that, then one day (after changing and drilling 3 stats) it cooled off. Didn't do it with the heater on. It was a desmogged motor with a bunch of tapped holes in the intake/water passages. I added a small (4AN ?) bypass hose to the top of the water pump. Problem gone. Never hurt anything, just bugged me.
  16. i should have mentioned in my first post , both thermostats have that 1/8" hole in them

    i'm still baffled why the two cars act differently
  17. sic-nic
    Joined: Sep 27, 2009
    Posts: 212


    yeah thats how i feel seeing how for almost 5 years that has never happened ! thanks for all the input fellas have a great christmas filled with new stuff for youir cars!
  18. henryj1951
    Joined: Sep 23, 2012
    Posts: 2,305

    from USA

    as long as it opens up....
    you are GTG...:cool:

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