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Old 05-22-2012, 11:20 AM
ianacole ianacole is offline
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Default Back for more help - SBC cooling issues

This issue just began a couple of months ago. Drove it all last summer with no issues, and in the winter I was worried that I wasn't getting enough heat into it. No changes other than the number of miles on it, but as of a month and half ago the heat started climbing. In a 30 minute drive home or to work it starts pushing 210 degrees. Radiator is hot top and bottom. No leaks. Truck is running just as it did last year - decent power, no backfires, no lugging, no more smoke than there has been previously, it's just overheating now. Need some advice on next steps.

Setup:
  • 73 FJ40
  • 75ish SBC, Carb'd
  • Stock sized radiator, 4-core, no shroud
  • 160 degree thermostat

What I've done:
  • Swapped the water pump (minor drip around impeller shaft)
  • When I swapped the water pump I checked the radiator for sediment buildup - looked clean
  • Put in a new thermostat (used same 160 degree)
  • Removed siezed fan clutch and put in new fan clutch
  • Replaced spark plugs - cylinder 1 looked ugly, a lot of gray ash buildup, the rest looked fine
  • Checked timing - looks okay
  • Turned up the fuel mix screw on the carb to run a little richer
  • Pulled the York compressor to minimize drag/parasitic loss
  • Checked hoses, don't seem to be collapsing
  • Replaced radiator cap
  • Replaced oil pump - doubled the oil pressure, but seems to have accelerated heat-up
  • Flushed and refilled with 50/50 antifreeze/water mixture
What's left to do, other than replace the motor? Could it be water channels plugging up? I could go to an aluminum radiator and/or a shroud, but this wasn't necessary last year. Am I missing something?

Anyone want to buy a truck?

Thanks all!

Ian
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Old 05-22-2012, 12:51 PM
SteveH SteveH is offline
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The standard Mud answer (and many other sources) is to fab a shroud for it. Over the years, the most vexing cases I have heard of were solved with a decent shroud.

You don't mention if it's overheating on the freeway, but if it's in town, I'd check the fan clutch performance under various heat conditions. If it does not overheat at 60 mph, then this points to a fan or shroud issues, as at 60 mph, the wind is doing the cooling. Just my .02 - others may see it differently.
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Old 05-22-2012, 01:07 PM
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rover67 rover67 is offline
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I agree that if you don't have a shroud for it you should make one. it really helps a lot. That is assuming your fan clutch is healthy.

Also, when you make the fan shroud, think about airflow through the radiator. Too many times I see people bolt a flat piece of metal to the back of the radiator, cut a hole in it for the fan, weld a ring on and call it good. The air needs to be able to flow through the radiator, out the back, then get channeled to the middle where the fan ins in some sort of nice gentle fashion.
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Old 05-22-2012, 01:32 PM
ianacole ianacole is offline
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Thanks Steve and Marco. I won't make the truck do 60, but the heat continues to rise
at 55mph. Original fan clutch was seized so I replaced it when I did the water pump about 3 weeks ago.

I've seen mention of using a Taurus shroud, or converting to electric fans. What perplexes me is that it didn't have issues last year.
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Old 05-22-2012, 04:22 PM
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If you have not changed anything do you have an air bubble in the system from sitting? I never ran a fan shroud on my 40. Never had any overheating issues until the engine caught fire But that's another story. 400hp stroked 383 by the way in SLC and Moab heat. Clutch fan, stock radiator, high volume water pump. Nothing fancy.

Don't get me wrong a should is a good thing. I just did not have the means at that time.
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Old 05-22-2012, 08:14 PM
ianacole ianacole is offline
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I drive it daily...It's gotten worse over the last month or so. What temps were you normally running, prior to the fire, on your 383? Is 210 on a SBC a reasonable temp?
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Old 05-22-2012, 08:56 PM
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have you done a pressure test on the cooling system to check head gasket integrity? not that this is a common issue with a SBC, but it might be worth a look.

Also, why a 160 t-stat? those are for race motors. you should be running at least a 185. I like the 'balanced' t-stats from robertshaw or milodon.
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Old 05-22-2012, 09:05 PM
ianacole ianacole is offline
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I have not, and that's a good idea. The 160 is what was in it, so I just replaced it with like components.
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Old 05-22-2012, 10:53 PM
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+1 on a higher temp thermostat. It is counter-intuitive, but really, a hotter tstat makes for a cooler motor.

Doubted, tested, then proven correct on a Honda XR650R hot blooded waterpumping beast. The theory behind it is, it allows more dissipation due to a higher temperature differential in the radiator. It really works. Eliminating the tstat actually made the motor run hotter... less dwell time and temperature differential.

So does Redline Water Wetter. Eliminates bubbles and increases surface contact for heat transfer.
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Old 05-22-2012, 11:03 PM
ianacole ianacole is offline
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Interesting. I up for changing out the thermostat. It looks like my options are 180 and 195 degree units. Which one would be better?
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