Thread: 496ci possible cooling issue

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Ok I have built a 496 bbc, aluminum heads, aluminum radiator, duel 10 electric fans pulling air through rad, 195 hi flow thermostat, electric water pump, timing set at 16 degrees, running 98 octane fuel, 11.5 comp.
Question I have that I can't seem to find an answer on is, it seems to run hot 220-225 on the gauge, but you grab the hoses and there cold then all of a suden they get hot and it cools down to 200. I have changed the autometer electric gauge to a mechanical with no change. I can't find anyone that can tell me if this is normal, one guy that builds engines says don't worry about it just run it as long as it doesn't get past 240 degrees which I will if I can get someone that has experianced something similar to say theres never had a problem. Any help would be great just don't want to kill it before it hits the trails.

electric water pump? which one and what set up? Do you have the bypass hose to circulate water within the engine until t stat opens?

10 inch fans? whats the amp rating?

Whats the engine in? a/c or oil cooler ? Tranny cooler in rad or in front??
Welcome aboard CHR

I don't have much faith in cobbled-up electric fan systems and even less faith in electric water pumps. They might be great for cycling a little water through the radiator on the trip from the top end back to the pits, but to run one on a full time basis is just silly to me. Do you have any idea what the pumping capacity of the pump is?

If I were building this motor, it would have an Milodon 16225 engine-driven water pump, conventional steel vee-belt driven 18" diameter, 7-blade fan with thermostatically-controlled fan clutch, full shroud and a Milodon 16401 180 degree thermostat. BULLETPROOF.

You guys who thing you're making hp with an electric water pump and electric fans are just fooling yourselves. It takes the same amount of horsepower to move a volume of water or a volume of air, no matter whether you do it mechanically or electrically.

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Welcome to CHR. Tech's got valid points on all fronts, but it sounds to me like you may have air in the system blocking your water flow, then after a bit it jumps some bubbles and you get a step change.

I don't know big blocks, but I suspect the thermostat.

Have you tried running it without? Or, better yet, if you have an old one, gut it and swap it, see what happens. Sometimes it is a good troubleshooting technique. It only costs a quart of coolant, gasket, and an old Tstat.

Originally Posted by firebird77clone

I don't know big blocks, but I suspect the thermostat.

Have you tried running it without? Or, better yet, if you have an old one, gut it and swap it, see what happens. Sometimes it is a good troubleshooting technique. It only costs a quart of coolant, gasket, and an old Tstat.

Just to cover the base, running without the t-stat is a great troubleshooting tool, but a terrible idea for normal operation. Slow to warm up to operating temperature (especially in frigid Maine), and in hot, humid areas will be prone to overheating because the residence time in the radiator is too low for heat transfer (coolant is traveling too fast to have time to cool). My opinion based on the experience of moving from MO to TX Gulf Coast 40+ years ago, and hammered into my head as the years passed. Like Tech pointed out, you've built in a bunch of potential headaches with your system. Don't make running without a t-stat another one.

My 2 cents says it's the thermostat.
If you got a cheap "poppet" style from a local supplier for like 5 or less. Rip it out and get a good "Sleeve" type. The sleeve type can flow more and have a smoother modulating transition, this keep the temperatures even. Vendors like Summit or Jegs show them as a "heavy duty or Hi Performance" piece. I usually see them for like 8 to 10 bucks.

And welcome to CHR too! Nice seeing you here.

OH! one more thing.. pictures are always most welcome.

I only like electric water pumps on drag cars where you go 1/4 mile and then you can circulate the water and electric fans pull air while adjusting valves / packing chute/refuel for next round.

An electric water pump and/or fans set up with thermostat and or temp sensors/relays is over the top for basics to go wrong.

Where is your temp sensors located and are your fans or H2O pump on temp controlled relays?

I agree with eveyone else pretty much but my guess is the reason the hose is going hot then cold is simply the opening and closing of the thermostat, next thing is where are you taking your sending unit temp off at? Tech helped me solve my issue on this, if its at the top of the manifold in a potential air bubble it could be measuring steam and not water. Next thing is whats to hot? I have read a zillion articles on this and all the older rodders tend to think 220 is way to hot when actually many of the newer daily driven vehicles are running that temp all the time to burn off carbon. On another web site the general answer was if it ain't pukin' water your not to hot, I don't know if I agree or not but with the newer lubricants that clearly can take hotter temps this might be better than running to cold, but you better make sure your cooling system can handle the pressure, the more the temp the more the pressure they are pretty much married together depending on altitude, your anti freeze also increases your boiling point as well but the higher the pressure the higher the boiling point also, if you operate high temps you have to make sure everything else can handle it as well.

All of the above, plus consider swapping the 2 10" fans for a single 16 or 18" unit.
Two 10" fans draw air thru 157sq/in of radiator, a single 16" draws through 200sq/in of surface area.

Originally Posted by tdkkart

All of the above, plus consider swapping the 2 10" fans for a single 16 or 18" unit.
Two 10" fans draw air thru 157sq/in of radiator, a single 16" draws through 200sq/in of surface area.

If the fan or fans are properly shrouded, using a piece of flat aluminum stock with the edges formed down to stand off of the radiator about an inch, they will draw through the whole radiator. The key is the flow rating of the fans, and the amp rating at shutoff head is a good indicator.

If it's an air bubble, then it could be effecting the tstat function. A trick for the fix is to drill a very small hole in the Tstat base, near center. This allows air to pass the tstat, preventing the bubble from delaying its operation.