1968 Firebird 350 Pulleys
 

Are all 8 bolt water pump pulleys the same diameter? Wondering if the air conditioned cars had a smaller pulley to increase fan speed? Car stays at 180 regardless of ambient temperature as long as it’s rolling however temperature rises quickly when stopped. Currently have 7 blade fan, Hayden heavy duty clutch, stock shroud, upper baffles (not lower), largest Cool Case radiator that will fit, water pump plates clearanced, and initial timing at 12 degrees with full manifold vacuum advanced. This is for my 1968 Firebird 350, stock, 066 cam with factory exhaust manifolds and dual exhaust. I fret when in traffic on hot days…

Ac pulleys for the water pump and crank are a different size than non ac.

https://www.teufert.net/partbook/67-76/1-i.pdf


Info for 67-69 pulleys and belts.

Solid proof there’s a smaller water pump pulley then. Crank pulley is the same for both AC and Non-AC. Thanks!!

Does your pump have the superior factory cast iron impeller and have you checked and if need be set the baffle plate to impeller clearance?

There are also a sealing rubber grommets in steel tubes that goes between the baffle plate and the timing cover on each side and there has to be a good seal made there when the baffle is pushed up against it.

If not shims can be had to raise them up off of the timing cover to get the needed compression and seal to be made.

Also your fan blades no matter how many should be spaced such that they sit half way in and half way out of the shroud .

210 to 215 degrees is not too hot when sitting at a hot idle with the AC on as long as the temps start to drop once above idle rpm and at 30 mph.

Are you boiling coolant out into your catch can at these times?

Have you got all the air out of your cooling system by burping it once the T stat opens and coolant flows?

8-bolt water pumps don’t use the two tubes like the later 11-bolt pumps. 8-bolt has two metal plates instead of one like the later

Ah. Thanks .

It’s been a long time since I had a 68 apart.

The crank pulley for ac is bigger 8” vs 7 5/16”

I installed the ac pulleys on my 68 Firebird and it did help to cool it

Yes. All the above has been done to include fan half in-out of the factory shroud. Found the smaller water pump pulley and will have that on hopefully later this week. I have a 19 inch flex-a-lite fan waiting in the wings to try if the new pulley setup doesn’t satisfy me. This is a non-AC car so the extra heat isn’t generated by that anyway… 210-215 may not be overheating but I don’t like it. So far it hasn’t belched coolant into the recovery tank. I never give it a chance. What is it about Pontiacs that makes them run hotter than other makes?? My big and small block Chevelles & Nova, mid sixties Mustang,, and late sixties Ford pickup would idle at 180-190 and never get any hotter no matter ambient temperatures. This Firebird just likes to FIGHT!

I’m a big proponent of those stainless flex fans, they really move a lot of air at idle. Have a 19” on my 66 GTO, albeit with a large 8” water pulley and a small 6.5” crank pulley to slow the fan down in relation to engine rpm. Runs at thermostat temp in any traffic idle conditions in south Alabama summers.
But I would caution over-driving a flex fan using a small water pulley, which would make the fan spin faster than engine rpm. With my setup at 6000 rpm engine speed, my fan is spinning at less than 5000 rpm. If you use the small water pulley you will spin the flex fan approaching 7000 rpm at that same engine speed, so be aware of that aspect. When Pontiac used those flex fans they were under-driven with large water pulleys

You should be able to get your cooling issue straightened out using a factory clutch fan. Our Firebird 400 (automatic) with factory cooling system used to heat up a little with the A/C on in traffic/sitting at lights. We installed a couple small pusher fans on the radiator that switched on with the compressor, and that seemed to work well enough here in AZ for 10 years. But over the winter I completely redid the cooling system so that I could jettison the fans. I installed a remanufactured 8 bolt water pump with the tall vanes, a new Cold Case radiator, a Robertshaw high flow 180 degree thermostat, and a Hayden 2731 clutch (a Cadillac part with longer snout so the factory fan sits .6" or so further in the shroud). I'm not sure which part or combination of parts is responsible, but the car no longer heats up in traffic or while sitting, even with the AC on 100+ degree days.

Good info. I’m running a 2.56 rear and a stock 350. Not much of a high RPM blast takes place. It’s a Saturday afternoon cruiser. I’ve tried two different fan clutches, fan positions, ported and full vacuum advance. Initial timing at 12 BTDC. Nothing changed the inevitable rise in temperature at idle and in a slow traffic (less than 10 mph) situation. Sort of my all in effort to keep this car a driver during warm weather without going all electric fan assemblies.

Agree. The FACTORY fan clutch would probably work but these made today are not the same. Sure, Hayden lists the Heavy Duty and Severe Duty clutches but the temps that either needs to fully engage makes cooling any engine a challenge. The engine has built so much heat by the time the clutch engages it is almost impossible to recover from in an idle and low speed situation. Tried both style clutches with a factory seven blade fan. The same result. The old fan clutches would engage at lower temps with more than 90 percent fan speed (compared to engine speed) and blow the hat off your head. My opinion.