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Questions on difference of water temperature within the Chevy small block.

Discussion in 'The Hokey Ass Message Board' started by grobb284, Jul 14, 2009.

  1. grobb284
    Joined: Jan 24, 2007
    Posts: 62

    from Ohio

    How large is the temperature gradient across a small block chevy with cast iron heads? The reason I ask, we are using an aluminum air gap intake, that has four access points to the circulating water, one in each corner.

    The sender for the gage was at the passenger side front nearest the thermostat. The temperature switch for the electric fan was at the drivers rear corner of the intake. The 190 degree fan switch came on at 215 according to the gage.

    We then reversed the locations, putting the gage sender at the rear of the intake on the drivers side, the fan switch at the front of the intake on the passengers side (common with the thermostat). This time the reading was 185 when the fan switch came on.

    I was surprised that an aluminum intake would have that much difference in temperature with the water circulating. I am confident the fan switch is repeating with consistency the temperature trip point, it's just that the water is much hotter at the thermostat.

    Anyone have some detailed information on the temperature differential at different locations of the water circulating the engine?
  2. ride00007
    Joined: Aug 19, 2007
    Posts: 47

    from Illinois

    This is a good question. I've often wondered where the best location for my sending units actually are. My temp sender is in the head... I'm not sure that's the best place.
    Wherever the sender is... it's just a quick picture of what's going on. Not sure which area is the most critical to observe and which is the hottest. I'm guessing there are a lot of variables that affect that.
  3. el Scotto
    Joined: Mar 3, 2004
    Posts: 3,833

    el Scotto
    from Tracy, CA

    I wondered this before, as well! There's a kit in the Speedway Track Catalog for directing water to a spot between the two rear cylinders, a buddy of mine says there is a hot spot there.

    We always wondered the difference between water temps at the manifold and at the factory temp sending unit in the head, too. Seems like it'd be much hotter near the combustion chamber.
  4. I would like to know as well. I have a fan switch on the right side that will activate the fan at low temps (150-160) displayed on my gauge. The switch is in between the rear cylinders and the gauge sender is on the left side between the front cylinders. The real issue with mine is over cooling in the cooler seasons. I think I will swap them and see if it gets better...
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  5. sdluck
    Joined: Sep 19, 2006
    Posts: 1,582


    Howard Stewarts (sp)web site has some good info , small blk chevy water pumps are not all created equal, the don't flow water the same to both sides,also cylinder 5 and 7 are next to each other in firing and tend to build more heat on that side.
  6. Most of the heat removed from an engine comes from the cylinder heads. I would fully expect there to be a 30F degree or more difference in the water entering the heads and the water leaving the heads.

    The only good way to measure coolant temperature is after its done its job removing heat from the engine and while its on its way to the radiator.
  7. squirrel
    Joined: Sep 23, 2004
    Posts: 37,075


    30 degrees sounds reasonable.

    The aluminum intake can't affect coolant temperature front to could it?
  8. oj
    Joined: Jul 27, 2008
    Posts: 5,440


    I have felt that water dosn't actually flow thru the engine, heat gets transferred from hottest to coldest (very quickly) by convection. If you stick your finger into the formost water passage port in the head and another finger in the water inlet in the block you can almost touch fingers, and that is where water flows. What i do on the race motors is feed water into the back of the intake manifold and return from the front of the block-the water has to flow thru the head.
    If your sending unit turns your coolant fan on & off you might want to put it on the radiator inlet, right in the stream coming into the radiator. That way it can run with the motor shut off and turn itself off when it reaches a temp. If the sender is in the block it won't be able to run on 'automatic' mode because it isn't cooling the engine, it'll just run and run.
    Last edited: Jul 14, 2009

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