Help Cooling experts!

I have a 1969 GS with a very mild 455 (1500 miles). Small cam, stage 1 valves w/ some head work, cast iron intake and exhaust manifold, 850 QJ jetted for 455, pretronix ignition.

Problem: It will run hot at idle on hot days. The gauge moves slowly but it will creep up on 210 and still climb if I let it. If I put it in neutral it will remane were it is at, and if I increase the RPM's in neautral it will decrease slowly.

-Timing is at 12 - 32(vac. advance is on ported side)
-180 deg thermo.
-Factory shroud and new 18" 6 blade thermo clutch fan, 1/4 out of shroud.
-New 4 core radiator.
-New water pump.
-bottom hose has spring

At anything other than stopped it is just fine. It seems to be a air flow issue.


also, how do you test a thermo clutch fan. The one I just replaced had some resistance, hot or cold, it was the same. (I could easily turn it with my pinky finger) The one I put one turns even easier

Any ideas? Thanks, james

 

This seems like a fan clutch issue to me. You may have answered your own question: simply not enough airflow at idle- essentially your fan isn't doing enough on it's own, it needs help from the car's motion. I'd recommend a non-thermostatic fan clutch on general principles, it's considered to be a 'higher performance' part, plus you can tell when it's failing by the wet discolored area on the clutch.

What temperature do you see around town? Is it a steady temp?
Are you losing coolant, but you can't see any leaks (I hope not)
Have you actually ever overheated? At what temperature, and in what driving condition? In traffic, I would guess.
Is the temp gauge electrical or mechanical?
Is the shroud factory correct for the 455 or your original 400? What's the difference in the two, if any? i don't really think there's a huge difference.

Do you use an overflow tank? It's for more than to just hold 'extra' fluid, the radiator will purge to and draw from the overflow under regular use.

The thermostatic fan clutch gets harder to turn the hotter the bi-metal spring gets.
The non-thermal fan is a viscous type which allows the fan to spin slower at higher speeds, but will 'clutch' more as the rpm is lowered- less parasitic power loss at higher rpms.

 

A non-thermal clutch would definitely solve your problem. They cut out at about 3500 rpm. Your other options would be a 165 degree thermostat or an electric fan in front to push air through.

 

Was the fan that far out of the shroud with the other fan ??

Also.....is it a rebuilt water pump or an NOS one ??

I've got a friend who rebuilds waterpumps and has shown me some interesting things you can get from other rebuild shops. He does a couple hundred THOUSAND waterpumps a year too.....

 

One more suggestion, check your idle adjustment... you may be too lean.
Don't overlook the 'free' stuff!ou:

 

What water pump pulleys are you using?
There were two types of pullies and water pumps. The non-A/C pulleys were almost the same size in diameter and the water pump had 6 blades. The A/C pulleys had a much larger crank and smaller water pump pulley. The water pump had 5 blades.
Most of the water pumps available today are the 5 blade A/C ones. Using the non-A/C pulley setup on an A/C pump will reduce flow at idle, yet may be ok at speed.
It might be worth checking to see if you have a mismatch.
Regards,
Mark

 

Do the A/C vs non-A/C pumps have different snout lenghts?

 

So if you use the 6-blade non-A/C pump, you'll get more coolant flow? Is this the cast impeller type or the alternator-fan type?

 

I have heard the answer is "yes". I use a/c pumps, because that's what the car that originally had my engine had...and I'm using the shroud from that car as well, so I figured, better keep it the same.





Also, I think only the aftermarket steel fans have 6 blades...pretty sure my Heavy Duty cooling fan has 7 blades, and it's original off my old Riv, or at least, it was there when I bought the car...I'm gonna go count (what a dummy but it will bug me). I'm fairly certain that the 7 blade fan also doesn't have the blades perfectly spaced.


The more blades will not increase the volume of water pushed by the pump...it's not the airflow that moves the pump, it's the belt, don't forget. The extra blades should increase airflow, though.

 

Hmmm. You mean that a cooling fan won't pump water? Damn, now you tell me! JK. In all seriousness, the original post referred to the number of blades on the PUMP, not the fan.

 

I must have misunderstood you, then

 

Try the $116 NAPA clutch for '85 Chev 454 truck. Solved my problem. 160 T-stat runs 160 until temps get 80-100 then runs 185 all day, city/highway.

 

Thanks, guys! Great information!

I think I will pick up the heavy duty 3/4 ton chev P/U thermo clutch fan and I will get a 160 thermostat.

What was the brand name of the better thermostat that is out there?

Does anyone know the diameters of the A/C verses the none A/C pulleys?

Thanks,
James

 

Why not try the following equivalents?

Airtex 2797TA ($62 from carparts.com)
Delco 15-4320
Everco A5570
4Seasons 36704 ($87, carparts.com)
Flex-a-lite 5649
Imperial 215045
Murray 271301
TRW FC 135
Hayden 2797 ($88, carparts.com)

 

Thermostats- Try RobertShaw HEAVY DUTY version....or Moroso makes them also(bought Moroso from Summit or JEGS). RobertShaw available at regular auto parts store...just make sure you pay a little more and get the HD unit...sometimes spending a few bucks more makes the difference.

Also....Chris, etc....thanks for the excellent advice on cooling and part numbers.....this site is EXCELLENT!!! Patton

 

If you go to Auto zone the Robert Shaw GenerationII thermostat. this heavy duty thermostat has a life time warranty. Thought this maybe a useful note.

Later

 

OK.....this is a pain in the ass (not really compared to a blown head gasket....) BUT I ALWAYS DO THIS with a new thermostat

Before installing.....put it in a pot of water and put a cooking thermometer in the pot NOT resting on the bottom. Watch the temp of the water come up and watch when the thermostat opens

I've seen brand new ones not work as advertised

just one more of those little things to do to avoid a headache later on and also to eliminate it as a later possible unknown variable

 

Runnin' cool

I run a 160 thermostat, half a bottle of water wetter, a non-thermal clutch fan(under $50 at Car Quest), a 7 blade metal fan from a '74 Monte Carlo, and an electric fan. Temp is 170-180 cruising in moderate to heavy traffic. Todd Borland can back me up on this... he runs the same setup.

P.D.

 

OK, I put in the NAPA ($$$$) heavy duty thermo clutch fan and a 160 heavy duty thermostat. It still runs hot at idle.

-80 day drove for 10 min it ran about 180. Let it run in gear in the driveway for 5 min it creeped up to 205-210. Put it in park and let it idle, and it started cooling down.

What is my next step? The water pump that is on it was new 1500 miles ago. Is there a better water pump out there?

Does anyone have some smaller pulleys to turn the pump faster?

I know that I can go to an electric fan to keep it cool at idle, but that isnt really fixing the problem?

HELP! (see first post for engine set up)

James