1970 BB Caprice

[brcol]

I'm struggling with the cooling system in this 1970 Caprice with a mild 402bbc.

My thoughts: This car should be able to cool naturally without the fans running while running 60mph down the highway, and the fans should cool it down to 180* and kick the fans off.

Car Specs: 402bbc, with 3872702 iron heads, low (8.5) compression ratio, Mallory Billet HEI replacement (14 initial and 32 including mechanical advance all in by 2800), Holley 750, Hyd Flat tappet version of the LS6 cam, Roller tip rockers, 700R4 with 2500 stall and lockup, Ron Davis radiator with 22x18 core, louvered shroud with 2 Spal VA15-AP70/LL-39A fans @ 1115cfm max ea, Edlebrock WP, March pulley set up with 7231 Cranksharft pulley to achieve 10% overdrive of WP (removed 7331 crank pulley that had WP 40% overdriven), 160* thermostat.

If you take off with the car cold, it will heat to 180* and stay there, once you have to stop at a couple of stop lights, or you start to accelerate hard, it'll climb to 200 and kick the fans on. Then it will slowly come back down to 190, but will rarely return to 180* and kick the fans off. While running in traffic or around town, it'll stay below 200. It will keep climbing past 200 if you continue to run it hard.

The car does have a massive A/C condenser out front. I mean this thing is like 2" thick and covers the entire radiator plus some more, and there is about 1" between the radiator and A/C condenser.



Thanks for any thoughts and guidance.

[JustJohn]

That actually sounds about right. I have a 69 Impala with a 454 and Griffin radiator/fan assembly. If you have a 180 degree thermostat, it's going to float around that number because the purpose of it is to heat the car up to that minimum temperature (and cool it down to that temperature).
You could raise your fan sensor point to come on at 190.

[brcol]

As stated above the car has a 160* thermostat in it. I ran a 180 for a short time, but it'd never kick the fans off then.

[WallaceMFG]

That fan shroud with louvers in it isn't doing you any favors. Air will always follow the path of least resistance, so the fans will pull air in those openings and back out the fans, doing nothing to cool your engine since it is harder to pull through the core. While driving, they can help with letting air bypass the fans, but you need to be going 45+ mph for this to be true.

The better solution is to use flapper valves. They can be pushed open by air coming through the radiator, but the fans will suck them shut when at low speeds and draw air through the core.

I would replace that shroud or modify it to have flapper valves then see how you do. I think you'll find a large improvement in cooling by doing that.

[JustJohn]

Missed information aside, your temperatures seem typical for the application unless you're climbing way above 200...

[btmatt]

32' total timing? I ran closer to 38-40 in my big block and it would run hot with less.

Man, I don't miss that "hot mess"

[brcol]

Thanks for the feedback gentlemen. I’m out of adjustment with timing in this distributor. Advancing any further is resulting in hard starting. May need to plop down the money for an MSD.

[thinkfastroth]

Had a problem similar to this on a 68 396 with l88 heads. Car would be cool at idle and low rpm but would climb as soon as it would go under load 200-240 but would cool down after brought the car back down to idle. We pulled the heads and found out that the motor had been built with marine head gaskets and a reverse flow water pump. Once we swapped gaskets and pump problem was solved and very rarely went over 200.

Car was 68 Camaro 396 w/l88 heads crane solid ls6 replacement cam , m22 trans and 4.11 rear, be cool rad with duel fans 19 lb. cap and 190 thermostat.

[brcol]

I talked to the manufacturer of the shroud this morning in depth and they are going to work with me to covert the shroud from the louvres to Spal 30130012 rubber flaps. They are interested in the outcome to improve their designs. Will keep this post updated with results.

I tried pulling the fans and the shroud completely off and taking off on the highway. Temp stayed under 170 at cruising speeds. The shroud is definitely a restriction.

[JustJohn]

I reread your OP again and you are correct, my car runs a steady 180 on the highway, AC on, no fans in SC summer weather. The main visual difference seems to be that I have flaps on my fan shroud.

[brcol]

On the plus side I went to a car cruise tonight that is mostly through city streets at 15-30 mph and it never got over 205*

[brcol]

Cut out the louvres today and replaced most of them with flaps, covered the remaining louvres with duct tape. Improved but not fixed, took longer to hit 200 and cooled to just over 180, but didn’t cool enough to kick the fans off. A few more flaps may get it really close.

More to come.