Overheating climbing a mountain

[jumpjets]

Hello, I’m a longtime reader, first time poster.

My 1978 K25 resto project is running great, but it overheats when driving up the Sierra Nevada mountains.
Tech stuff:
-383 SBC (mercury marine block)
-9.5:1 compression
-Moderate cam (boat cam)
-Summit iron vortec heads. 64cc chambers
-Aluminum dual plane intake
-HEI distributor. 14* base timing, 32* at 2200 rpm
-Edelbrock 600 carb
-87 octane gas

-Summit brand 4 core alum radiator. 33” x 20” (stock size for K25)
-Dual 1300cfm electrical fans with shroud (on at 190*)
-Stock spec water pump
-180* t-stat

-TH350 TCI crate trans.
-1800rpm stall
-33” tires
-NP203 T-case with full time 4wd delete
-stock 14 bolt rear. 4.10 gears (I think)

I had assumed this setup would be great for Death Valley and the sierra mountains, but it can’t climb the mountains. It’ll run about ~200* down the highway at 65mph, even in 100* ambient heat.

Once I start climbing 6-10% grade at 30mph, the truck gets above 230* and temp keeps climbing.
I’ve thrown a ton of new parts at this thing, and the whole rig has 1k miles on it. I even tried putting the T-case in low gear and left the front hubs unlocked.

Any tips or recommendations?
-more timing?
-water only instead of 50/50 mix?
-remove T-stat?
I’m running out of ideas. I had assumed this thing would pull a trailer uphill with the AC on. It can’t even get me & my dog uphill with an empty bed.

 

[jumpjets]

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[PrairieDrifter]

I've heard of some of the more expensive brand radiators have problems cooling. Something like the cores are too close or the fins are too dense. Basically they can't move enough air.

Only thing I would recommend is verify you have a properly working thermostat, you should heat water up to the specified temp and actually check the thermostat functions properly. Also keep the antifreeze, maybe even bump up the antifreeze ratio. Other than that, your fans may not pull enough air, I always use a mechanical fan, with a proper fan shroud, then if necessary a secondary pusher fan on the front of the rad.

Are your electric fans operating properly? Are they coming on at the right temps? Are they getting enough amperage? What are they rated for?

 

[PrairieDrifter]

You have an obvious big issue if you can't pull 35 without overheating. Especially if the temp just keeps climbing.

 

[jumpjets]

I think I found the culprit. I pulled the temp gauge sensor & dropped it into a pot of boiling water. The needle shot up past 240*, which is physically impossible. Once water boils, it can’t get above 212*. I shot the sensor & water with an IR temp gun just to verify. My Equus brand temp gauge was reading about 30* high.

I also boiled & checked my thermostat. No issues. If anything, my fans come on a little earlier than they should. It’ll idle all day with no heat issues.

Looks like the truck is doing just fine and I’ve been chasing my tail over an inaccurate gauge.

 

[PrairieDrifter]

I think I found the culprit. I pulled the temp gauge sensor & dropped it into a pot of boiling water. The needle shot up past 240*, which is physically impossible. Once water boils, it can’t get above 212*. I shot the sensor & water with an IR temp gun just to verify. My Equus brand temp gauge was reading about 30* high.

I also boiled & checked my thermostat. No issues. If anything, my fans come on a little earlier than they should. It’ll idle all day with no heat issues.

Looks like the truck is doing just fine and I’ve been chasing my tail over an inaccurate gauge.

I was going to mention the accuracy of gauges but I assumed you had your gauges figured out.

It's usually one item with cooling issues.

 

[Matt69olds]

Hopefully you were trying to fix a problem that wasn’t really there.

Only thing I would add to the discussion is shrouding and baffles. Make sure the radiator seals are in place and fit tight against the core support. Make sure any air that enters the grill has to go thru the radiator.

 

[jumpjets]

Hopefully you were trying to fix a problem that wasn’t really there.

Only thing I would add to the discussion is shrouding and baffles. Make sure the radiator seals are in place and fit tight against the core support. Make sure any air that enters the grill has to go thru the radiator.

Ah. I have neither of those things. My fans are nice and tight to the radiator back end, but I have no aero help in front by the core support. I’ll rig something up this weekend.

 

[DoubleDingo]

Sounds like you're on the right track. Climbing Sherwin Grade will test the best of rigs