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  1. #1
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    Advice needed - LS3 running hot(??)

    Hey guys, I know a lot of you are running LS power and I need some help solving my heat issue. My engine is new (bored and stroked LS3, 418 cu.in.), and only has 250 miles on it. The first 200 miles it never went above 210 but lately it's been hitting 230 on my gauge. I swapped out the factory style thermostat for a MR Gasket brand 180 which states the engine will run cooler. "Not Happening"! So knowing I didn't have an issue at first and all of a sudden started; does anyone have any experienced suggestions? Note: the 230 I'm getting is on a 75 degree day. I'm in Northern CA so will definitely see 100 degree days with my A/C on. I also have an Autorad radiator complete with shroud and 12" and 14" fans. The fans come on at 200. I need to solve this now. Your feedback is much appreciated.
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  2. #2
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    It is not uncommon to have air trapped in the block leading to overheating. Using one of these to evacuate and then fill the system will eliminate air pockets.

    https://www.ebay.com/itm/Universal-C...QAAOSwP25a2Yd3

    Don
    1969 Camaro - LSA 6L90E AME sub/IRS
    1957 Buick Caballero - huge project
    1959 El Camino - Ironworks frame
    1969 Mustang Sportsroof
    1956 Cameo - full C5 suspension/drivetrain

  3. #3
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    Is the water pump turning the right direction?
    Possibly air in the system?
    Did you put some coolant in the overfill tank so that the radiator will pull the fluid back in as the system cools?
    Are the fans running at full speed?
    How are the fans being controlled?
    Is the full area of the radiator exposed? Sometimes the core support needs to be widened to utilize the full area of the radiator.
    Are you sure the gauge is correct?

  4. #4
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    I really appreciate the responses so far.
    - I will look into getting my hands on a purge tool as it "is" possible there is still air in the system. I just don't understand why there were no issues during the first 200 miles.
    - I do have coolant in the overflow tank.
    - As far as I know the fans are running at full speed and are controlled by the ECU (or trinary switch on a/c)
    - The full area of the radiator is exposed. I have the Autorad wide radiator mounted the their aluminum core support which is made for the wider radiator.
    - I can only assume that the gauge is correct but I'm certainly questioning the sending unit. They are both brand new from Autometer.

    I think I answered all the questions. thank you *** Do either of you think my oil temp may be causing this? I don't have an oil temp gauge and I'm only running a stock type 5 qt oil pan since that is the only one that has clearance for my TCI subframe.

  5. #5
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    Quote Originally Posted by cwmusser View Post
    I really appreciate the responses so far.
    - I will look into getting my hands on a purge tool as it "is" possible there is still air in the system. I just don't understand why there were no issues during the first 200 miles.
    - I do have coolant in the overflow tank.
    - As far as I know the fans are running at full speed and are controlled by the ECU (or trinary switch on a/c)
    - The full area of the radiator is exposed. I have the Autorad wide radiator mounted the their aluminum core support which is made for the wider radiator.
    - I can only assume that the gauge is correct but I'm certainly questioning the sending unit. They are both brand new from Autometer.

    I think I answered all the questions. thank you *** Do either of you think my oil temp may be causing this? I don't have an oil temp gauge and I'm only running a stock type 5 qt oil pan since that is the only one that has clearance for my TCI subframe.
    I would not suspect an oil pan. I would bet air pocket in the system. At least that should be the first thing you check.

    Don
    1969 Camaro - LSA 6L90E AME sub/IRS
    1957 Buick Caballero - huge project
    1959 El Camino - Ironworks frame
    1969 Mustang Sportsroof
    1956 Cameo - full C5 suspension/drivetrain

  6. #6
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    Based on your answers I'm also leaning towards air in the system or cooling fans aren't running. Don't forget to turn on the interior heater to make sure there's no air trapped in the heater core. Is the temp going up to 230 even when you're cruising down the highway at 60 mph or only when standing still?

  7. #7
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    I'm in agreement that "I must" still have trapped air in the system. My dual fans are both on and blowing quite a bit of air. I will run my heater and try bleeding this thing again. It is getting up to 230 either sitting still or driving at low speeds, maybe up to 50 mph. I haven't had it on the interstate since the problem started. I have contacted Jim at Autorad (Jim is very helpful and knows my system best), and get his best tried method of "burping" the system.
    Thanks again to both of you for your feedback. - Carl

  8. #8
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    Are your fans moving air in the right direction? They should be sucking, not "blowing." (Sorry if this is too obvious.) Staying cool at higher, prolonged speeds would indicate a (lack of flowing air) problem here . . .

    When I had my (used to be two) fans hooked to the ECU, control sucked and was inconsistent. When I got a cheap (20 bucks) controller (and turned off ECU control via HP Tuners--otherwise, you get check engine light) that just turned them both on right now, all was fine.

    The 180 degree thermostat might give you issues in colder weather, as stock should be 195-ish. As a final point, coolant temp sensors are easily broken without physically noticing . . .

  9. #9
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    burping the system is a must..

  10. #10
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    Fill your radiator through the top hose (directly into the engine) after filling radiator before cranking. I think others have also had luck with raising either the front or rear while running (to get rid of the air pocket).
    Chris
    1968 Chevy Camaro SS
    LS3/T56 Ridetech suspension


  11. #11
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    I chased a hot running LS3 when I first got it in for a long time. Even sent the waterpump back to the manufacturer. Like you everyone suggested an air pocket. I did the usual tricks of jacking the front end up and filling from the upper radiator hose. None of that fully got the air out. I've since learned I can leave the car level and fill from the radiator like normal. The only thing I do is remove the steam vent hose (engine side) when filling the radiator. I leave it disconnected until water/coolant flows out and then hook it back up and top off the radiator.

    For me, it's easy to know when there is air in an LS system. If the motor runs hot at low RPM but cools down at higher RPM then it's most likely air. For example my motor ran hot cruising down the freeway at 70mph in 6th gear at ~1,700 rpm. As soon as I downshifted to 4th and brought the RPM's way up it instantly cooled off.

    good luck.

  12. #12
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    Thank you for your feedback on your experience. I have spoken with the builders of both the cooling system and the engine. If I put both of their remarks together it's exactly what you're saying. Autorad says to fill the system normally and let the system fill itself through the recovery tank (just keep it full while all this is happening), and the machine shop told me to remove the hose coming from the vents on the head and let water run through it until it's a solid stream.
    I'll be doing this today. Thanks again!

  13. #13
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    To those of you who responded to this original thread, I finally got to the bottom of my overheat issue. When someone builds you a custom radiator that's a dual cross-flow style, it's important that they remember to weld in the baffle that separates the top half from the bottom half. Mine was missing! My coolant had the ability to enter the top passenger side and just drop down and exit the bottom passenger side without going through the core. Not good!!
    Anyway, all fixed now and running like it should. My radiator supplier just kept telling me "it can't be the radiator". WRONG!!

  14. #14
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    Quote Originally Posted by cwmusser View Post
    To those of you who responded to this original thread, I finally got to the bottom of my overheat issue. When someone builds you a custom radiator that's a dual cross-flow style, it's important that they remember to weld in the baffle that separates the top half from the bottom half. Mine was missing! My coolant had the ability to enter the top passenger side and just drop down and exit the bottom passenger side without going through the core. Not good!!
    Anyway, all fixed now and running like it should. My radiator supplier just kept telling me "it can't be the radiator". WRONG!!
    That's annoying. I've also heard of this happening once before. Glad you got it figured out!

  15. #15
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    Damn, how did you figure that out?

    Don
    1969 Camaro - LSA 6L90E AME sub/IRS
    1957 Buick Caballero - huge project
    1959 El Camino - Ironworks frame
    1969 Mustang Sportsroof
    1956 Cameo - full C5 suspension/drivetrain

  16. #16
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    The side tank did not show signs of a welded seam where the baffle is typically welded in at the half way point so I was suspicious. I finally fished a wire down through the side tank and it just kept going all the way to the bottom. I have threaded in bungs so it was easy to get access. I was actually able to run a 1/4" hose in the top and down and out the bottom. Very disappointed that it wasn't built right.