Originally Posted by 71 chevy

I read on stevesnovasite that single pass is far better at cooling than double pass.

Originally Posted by BRAAP

Tad,

Doc’s post should be your starting point in figuring out what is going on.



Air flow is EXACTLY where I’d start as well. Been there done that trying to improve coolant flow, capacity, time in the radiator, LOTS of different thermostats, temp ranges and styles and none of that helped at all. Air flow mods is what helped the V-8 Z car stay cool.

Also, regarding the Thermostat, it seems to get a lot of attention whenever overheating comes up and most of the advice given will be centered around the thermostat. Granted, the thermostat is a common fault in some overheating situations, but when a few different thermostats have been tried and there is no change in "how" the overheating react, chances are the "cause" for the overheating is related to something else.

Due to how A/C functions, when it is operating, it is pulling the heat out of the cab of the car and expelling that heat to the atmosphere just ahead of the radiator in the condenser. As such, when the A/C is running, any air that goes through the condenser first is getting preheated so by the time it gets to your radiator, what air flow you do have through the radiator doesn’t have as much "room" left for more heat, (delta "T") i.e. the air through the radiator is already hot, so it can only accept very little more heat so the radiator remains hot! That is why your over heating issue is worse with the A/C running vs not. As mentioned earlier, when the A/C compressor is running, it is loading the engine a little bit more, causing the engine to work just a little bit more, absorbing a few HP at most, but that is nothing that would make the difference between overheating or not.
Remember, your cooling system and even the A/C system, in their simplest forms, are merely “heat exchange systems”. Cooling system is exchanging heat produced by the engine out to the atmosphere through the radiator. This system works pretty well in most cars, adequate for L-6 Z cars, barely adequate to not adequate for most V-8 Z cars. This inadequacy is mostly due to inadequate air flow thorough the radiator so the radiator can do its job in exchanging heat that it pulled from the engine out to the atmosphere. ;-)

Chances are your radiator is up to snuff. Your water pump and its driven speed as well as the thermostat are up to snuff. When the car starts to get warm, I'd be willing to bet that that temperature of the fins near the out of the radiator into the water pump is not much cooler than the fins near inlet of the radiator, where the coolant come in from the T-stat. Blow more air across the radiator and that temp difference from inlet to outlet of the radiator should become much greater, and the engine temp will also come down, i.e. cooling system is up to snuff, inadequate air flow "across" the fins of the radiator!

My first V-8 I struggled with wanting to run warm as well. Using that formula that Doc supplied, I spent several months making changes. Every change I made to improve coolant flow and soak in the radiator made NO difference! Every mod I did that improved air flow to and through the radiator, DID make a difference. Then after the wind tunnel testing results came out, that solidified my finds that the Z car is weak in the are of air flow “across” the fins of the radiator, and a super wonder fan, in itself is not the wonder cure.
Here is a brief run down on what I did.

Car;
’75 280-Z, non vented hood, mild SBC 350, T-5 trans. No front bumper, no air dam. Car ran consistent 12.3 @ 113 MPH, was a daily driver!

JTR GM radiator, Cheapo 14” slim fan.
As much under drive for the water pump as I could get with stock pulleys.

I first approached coolant flow mods. Like everyone else, I thought it was flow related.
1) Tried colder Thermostats, high flow thermostats, no thermostat! No change, car wanted to run warm, different thermostats only changed how fast and when it happened.

2) Found a crank and water pump pulley that went from under drive to over drive! No change! Still wanted to run warm, warmed up at the same rate etc. .

3) Disassembled the water pump, added a backing plate to the impellor and pressed the impellor closer to the housing, i.e. less clearance between the impellor and the housing and made the impeller MUCH more efficient at moving water through the engine! NO change! Still ran warm and heated up just as quickly! Though with the rad cap off and when the thermostat was open, (car running warm), there was noticeably more/faster running coolant through the radiator.

4) Removed the water pump and tapped the coolant bypass hole in the passenger side of block just under the water pump for a pipe plug, plugged it and drilled a small hole in that plug to restrict the amount of coolant bypass (thinking it may be short cycling too much hot water). NO change, car still ran warm, warmed just as fast!

5) Removed the engine from the car, (forgot exactly whey, I think it was oil leak related and ended up replacing all the gasket on the engine). Any how, when I removed heads I used different head gaskets with slightly different cooling passage ports! No change, car still ran warm!



Then I looked at the amount of coolant thinking it didn't have enough coolant and was just passing what little coolant it had through the radiator too quickly so it didn't get a chance to exchange the heat to the atmosphere! Bought larger NASCAR Style radiator, (3 gallons of coolant vs 1 gallon). Theory was to more volume of coolant in the radiator has more time to exchange its heat to the atmosphere.
Car still ran just as warm, just took longer to get there, but also took longer to cool back down as well! :shock: The added volume of coolant acted as a heat ballast/heat sink! In other words, no change, car still ran just as warm, just took longer to get warm AND longer to cool back down!


Played with the car sitting still at home, allowed it to warm up and get up to approx 210 degrees, then lightly misted the radiator with garden hose, temp came right down! Let it warm up again, blowing air across the radiator from a distance with an air nozzle, (don't get too close or the air blast from the nozzle will deform the rad fins). Temp came right down. Ahh haa...
With that I started to make changes in air flow through the radiator. Not having any of the info from the wind tunnel, I was going at it blind, so only made few changes and they ALL helped, making noticeable difference.

Sealed the radiator to the core support air tight so no air could go around the sides of the rad, but only through it! Plugged all the other holes in the core support except the big one in front of the radiator! ;-) Sealed the hood to the upper rad core support so no air could flow between the hood and the core support! All this made the biggest difference of everything tried, improved the running warm situation noticeably, almost curing completely! My license plate was in the middle of the grill, removed it, that made just a little more improvement. That is as far as I got with it. With what I know now, I would’ve ran the smallest lightest radiator, (JTR radiator), done an air dam and a flat plate from the air dam back to at least the rad core support and sealed all that air tight. Built formed sheet metal air entrance that starts at the same shape as the grill opening and transitions to the hole in the rad core support.

Hope that helps,
Paul

Originally Posted by terryr

It takes slightly more pressure to push it through.

I like the WTF factor. Dood, your hoses are on the same side!!! That won't work!!!!

Originally Posted by poconojoe

hench the name dual pass