Ok guys, you are used to me doling out advice, now it's my turn to ask! Last summer I put a 1975 350 in my 79 Formula, it hasn't been rebuilt, in fact all that has been done is a new cam/lifters/timing set and all new gaskets and freeze plugs. It has a th400 trans and had 2.73 gears. I only drove it a few times before summer ended and noticed it ran hot (220-230F) even with a new water pump and 160 thermostat and the 3-core rad that came with the car. Fast forward to this summer, it now has 3.42 gears and the difference in performance is great. However the heat problem remains. The rad has been changed for a brand new 3-core rad, the t-stat tests fine and opens fully, there are no air locks (I filled the rad with the t-stat out until the engine was full) and I checked the gap between the water pump impeller and the divider plate (about .030"). When I start the car cold and let it idle it warms up so fast, the t-stat opens after only 3-4 minutes of idling and flow seem ok thru the rad. When driving lightly around town I get about 15 minutes before the temp climbs above 220 then the only way to keep it from getting hotter is to turn on the heater full blast and head for home. On the highway at 65mph (3000rpm) it gets to 230+ after only five minutes, yesterday it got so hot the fuel system vapor locked and I had to wait for 1/2 hour with the hood open for the temp to come down so the carb would get gas. The timing is OK, 10 degrees base and 32 total at 2700rpm, plus vacuum advance (stock HEI, 1975 350 2bbl), the plugs are light to medium tan/brown so it doesn't appear to be lean. I'm using 50/50 mixed water and antifreeze and I've tried a 7 blade flex fan from a pickup truck and the 5 blade clutch fan that came with the motor, no difference. The pulleys are a matched set off a 76 400 wagon. I've confirmed these temp readings with an infra-red temp gun. I'm not looking for advice such as "use special coolants" or "try an electric fan", the factory didn't need that stuff to make it run cool, so why should I need them now? There is something not right that I'm missing, just need to figure out why this motor makes so much heat so quickly and holds on to it. By the way, the temp has not been higher than 78F on any day I've driven the car, so you can see why it is baffling. If I can't figure it out, anyone want to buy a Formula?
Steve  

Do you have a hot air duct running from the exhuast manifold to the air cleaner if so check to see if it opens when it warms up if not the vacuuum switch is bad.  

Nope, no hot air duct. One of those things I haven't got around to yet.
Steve  

Have you checked to see if the block might be pluged up by pulling the 2 drain plugs on the side of the block.  

I have seen the water pump baffle plate almost gone on some of these motors. You might pull the pump off and look. I replaced mine with one of the stainless ones. Look at the lower hose before you do anything it could collapsing from the water pump sucsion and you have to use a wire reinforced one. I used one of the high flow aluminum replacement water pumps and it would suck a new molded hose flat as a pan cake. Also depending on your allittude and grade of gas you could be a little advanced and with the great gas we get now you could also be a step lean, but those things alone should not cause you to run that hot. GOOD LUCK let us know what you fix is.  

Also check the balancer to see if it has spun giving you a false timing reading that happend to me on my 301.Are you sure the clutch fan is working properly I always prefer a bolt on fan my self.Also if the engine is equipped with a early fuel evapporation system the butterfly on the exhuast could be stuck closed.  

Guys, thanks for the input. I've just had the water pump divider plate out to check the clearance between it and the impeller and it was fine, I've tried both the clutch fan and a 7-blade flex fan from a pickup truck and the shroud is fine as well. The rad hoses are brand new last summer and the lower hose has the support spring in it. I was running 87 octane because this thing is only 7.5:1 CR, but when the tank was almost on empty, I put about 5 gallons of 92 octane in it to try, that was the night it left me on the side of the road! There is no EFE flapper in the exhaust, I did away with it when I had the duals put on. At this point, I'm starting to lean towards the plugged block or slipped balancer. Although I had the frost plugs out when I re-gasketed the motor and it didn't look too bad, might be worthwhile to pull the rad hoses and flush out the block. I'll check that stuff tomorrow morning and let you know. Thanks again guys.
Steve  

I thought about this off and on today. Just one other thing you might check, the fan from a pick up. This may sound over obivous but it could be a GM reverse driven fan. Most GM serpintine set ups are reverse driven pumps ie. fans????????    

No, it's off a seventies chevy and it is the correct pitch for standard rotation. Saw a problem with a454 RV one time, somebodt put a revrse rotation water pump from a serpentine equipped motor on a v-belt motor, it would cool ok at low speed but not on the highway.
Steve  

Guys, a little update on my heat problem. Two nights ago I was messing around in the garage, wanted to cure the rough idle I was having (the cam is only 272 degrees and 450" lift) so I tried using Chevy rocker arm locknuts and 7/16" flat washers on top of the rocker balls to make a poorman's polylock. Found I didn't need the washers, the driver's side all ended up tightened down where the stock nuts would have been, but the passenger side all ended up about 2 1/2 turns up the studs from stock, and now it idles better. I have to assume the right head has been milled to correct warpage and the resulting excessive lifter preload was keeping the valves slightly open. Didn't test drive that night.
Next item, tonight I removed the rad and water pump to check for blockages, flushed the entire system with water, checked the water pump for the correct impeller (it is the same as the original and the new one I bought just in case) reinstalled everything and force filled the system by removing the heater hose at the back of the right head and pressurizing the engine with the garden hose until water came out the sensor fitting next to the t-stat housing, couldn't believe how much air came out! I reinstalled the hose and sensor and topped off the rad with straight water. Started the engine and ran it for almost 15 minutes with the rad cap off, it came up to 160 on the guage and the stat opened for a few seconds and the rad flowed fine, the stat closed and I added a bit more water. I Let it idle a little longer and the guage never went any higher! Unfortunately, my wife had to go out, so I couldn't road test it tonight, but this looks promising. Will update when I know more.  

Guys, an update on the heating issue. Despite knowing that my factory guage was inaccurate by 20 degrees, I installed a mechanical guage to make this easier. Now that I've flushed everything out the motor runs about 190 around town and 210 at 65mph, but if I push any faster it still creeps up to 220. I'm thinking that the old block and heads are too full of rust from sitting around for 20 years and aren't transfering the heat or there maybe a problem with the head gasket cooling passages. Either way this problem will have to wait until I build my 400. I hate to give up, but I'm not spending more money on this problem for a throw-away engine.
Steve