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Happy to see everyone is in agreement on slowing down coolant is a bad idea. Living only an hour from Palm Springs we get hot and is a great test bed for finding out what works and what doesn't. We have tested and proven to our satisfaction that a properly working thermostat and no thermostat both cool equally as well. What this means is that there is enough restriction in the complete cooling system that the thermostat is not the bottleneck in the system and no thermostat doesn't allow any additional flow over a fully open thermostat. So it's always a good idea to simply pull the thermostat out when testing to find cooling problems. Using the pan on the stove with dunking new thermostats and checking with a thermometer has shown that three out of four new thermostats open very late - and the expensive ones have as many problems as standard thermostats. It's not that great of idea to leave it out during cool weather, and always a good idea to put a good one back in after the testing is over. Maybe the simplest explanation of flow can simply be stated that even if the coolant is flowing twice as fast (it's not), it would return to the radiator twice as fast, and in the process the better flow gets into the nooks and crannies of the block and heads and helps eliminate hot spots.

Another often overlooked problem is the size of the bypass hole from intake crossover to the water pump. If you are running a thermostat the bypass should remain functional, but what originally started out as a hole somewhat smaller than 3/8" of an inch erodes to 1/2 to 5/8" in size. The hot coolant in the crossover needs to travel through the thermostat housing and through the radiator. The bypass hole allows coolant to short cut back into the low pressure area of the pump and return to the block to go through another heat cycle with no cooling. Figure that an enlarged hole can recirculate a third of the coolant without going through the radiator. I always round out the hole and thread it with a 3/8" pipe plug with only a 1/4" hole drilled through it. This allows necessary circulation after a cold weather start so the thermostat "reads" coolant temperature without having to wait for the block to heat the stagnant section of coolant under the thermostat. The drilled holes in the thermostat do about the same thing to allow the thermostat to read temperature, but I've found out that a couple 1/8" holes drilled in the thermostat on a really cold run can pass enough coolant to keep engine temps too cool.

Fan clutches not only wear out, some are basically defective at time of sale. The manufacturers are setting fan clutches up to start to engage when water temperature is 210° and not fully engage until 220°. It's not for everyone, but a lot of us in our area use the Severe Duty Hayden 2797 clutch fan and tweak the thermostatic coil so the clutch comes on at about 185°. Go too far and the fan stays engaged even on cool days, but get it right and it is another tool in keeping things cool. We've had a couple club members pull the severe duty clutches back off because of fan noise, but I prefer to run cool enough to keep the A/C running on the hottest days.

A/C equipped cars came equipped with a 19.5" seven blade fan - that still in place?

Did you check timing? As others have said, retarded timing generates a lot of heat. Figure your 335 HP engine had a true 10.25:1 compression ratio when new (advertised 10.75:1), and the valve job probably included a slight mill on the 670 heads bringing the compression up a little further. Kind of a loosing proposition in that timing has to be retarded to subdue detonation with that high of compression ratio and the retarded timing itself will increase heat and require retarding timing even further. I had a 455 that could only tolerate 28° total timing and it was a challenge to keep it from over heating. Mix in a little race gas so timing could be upped and it ran cool. Was a relief when we rebuilt it and lowered compression so there was no further need for expensive fuel.
 

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As a side note to this thread what do you folks consider normal operating temp for a Pontiac V8? 200-210? What temp should we be concerned at 225-230?

Thanks
 

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Yes I would like to know that too and I understand every engine build and tune can bring different temperatures, also another controversy I keep reading about is 160 or 180 degree stat, Butler told me they always use 160 in their motors so that's what used for a couple of years on one of their 461 motors, now I just switched to a 180 because I have no choke so I'm thinking it would warm up quicker and I was having overheating issues when I wasn't moving. Guess I went down the rabbit hole of leave it in the radiator longer but now after reading this thread I hope I didn't make a mistake.
 

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As a side note to this thread what do you folks consider normal operating temp for a Pontiac V8? 200-210? What temp should we be concerned at 225-230?

Thanks
Yesterday, Jersey was in the mid 80's with stuffy humidity, and leaving my car idle in the sun for an hour, it didn't break the 190 mark. I hope I keep it there!
 

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Thanks for the quick response. You're right about the OEM temp - way too high. But, the EFI readout looks realistic. May I ask what kinds of temps you are seeing now and the outside temp? Thank you!
Running around 185F, in California so usually sub 80F outside temp. If in traffic, temp will run towards 195-205F but quickly comes down when driving again.
 

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I've only had mine out twice and it was good but it's only been in the low 60's so we'll see when it's July and 85-90. I did get caught behind some huge farm equipment for a couple of miles going 20mph in 3rd gear and my temp got up to 200 with only my electric puller fan on.
 

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I also prefer the 160° thermostat. Basically the 160° or 180° should be fully open before the engine reaches 190°, but in the real world a lot of the lower thermostats wait until 175° to fully open and the 180's fully open at 200°. So choosing the lower number just gives a head start on cooling ability. I'd much rather hit the base of a hill with the engine a little cooler because the load climbing up the grade is going to raise temps. Say the grade adds 20 degrees and I'd rather go from 160 to 180 than 180 to 200. Here's a write up I did on PY Forums years ago. I thought I had reinvented the wheel but since then have found the same procedure listed years before I thought of it. This is on the 2797 clutch but should work on others. Some clutches might have a different coil mounting tab and you might just be able to move the coil over without re-bending it.

My disclaimer is “results may vary, and try this at your own risk”. I took a new severe duty Hayden clutch fan and re-indexed the valve on the front of the clutch. This fan has the coil thermal spring permanently mounted to the center pin and the outside spring tip dropped into a cast slot where the spring can be lifted out.

The pin controls the fluid coupling. As the pin is rotated counter-clockwise, the fan engages more. Best way to verify this is to take a hair dryer and apply heat to the coil while the clutch is sitting on the workbench and observe the motion of the center pin as the heat is applied. The object is to have the clutch believe the spring is seeing more heat than it actually is, and the spring needs to be bent to slightly move the center pin in a counter-clockwise direction. Very little adjustment needs to be done and it is easy to over-do the bend. The danger is that the spring could snap off and the fan clutch would be scrap. The actual change needed is to bend the end tang about 5°. Another way to look at it is to make the bend thinking of the minute hand on a clock and move the tip of the tang from 12:00 to about 12:05. It doesn't take much bending, and it's best to start out with very small changes.

Moving the tip of the tang clockwise results in the main spring body moving counter-clockwise which is where it needs to be to engage earlier. While Hayden advertises that the fan engages at 185 air temperature, every fan I've seen waits until about 210° water temp to ramp up. When I got my A/C working the temps wanted to stay right at where the fan clicked in, so I cheated and made the fan come in sooner. My initial attempts were always too much, so try to just barely bend the tang.

I've modified four fan clutches now, and have been happy with the results. Also, I am still running the 8-bolt water pump on all my engines and have found no difference in cooling between the early 8-bolt pump and later 11-bolt.

Fan Clutch Alteration.jpg
 

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Hello! I know this topic has been discussed ad nausem but one more question, please. Car is 1967 400/335. Engine just fully rebuilt. Car ran hot before rebuild. Runs hot after rebuild. New 4 aluminum radiator. New EFI. New high volume water pump. Timing seems to be set optimally. Water wetter. Now that temps are getting warmer, runs hotter. At 55, temp around 210...but stopped at light or stop and go traffic, temp shoots up immediately to 230 or so....perhaps more but I haven't put myself in a position where it could. Electric fans didn't help. Tried various thermostats, didn't help. So, desperation. Has anyone tried waterless coolant like Evans? Any meaningful results? As always, thank you.
Ive been running Evans in my 66 389 tri power for 2 years now, and I have had tremendous results. I rebuilt the motor 2 years ago and since it is very important to remove all the water from the cooling system I thought it would be a good time to switch. It was idling in my driveway on a hot and humid day at195 degrees. I’m very happy with it.
 

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Yes, I run the 160 degree thermostats and drill 3 holes like Army does,.....

mine runs real cool,....4 core US Radiator with oversized Down tubes, 7 blade fan, heavy duty temp fan clutch, proper shrouding, flow cooler water pump 11 bolt, plates tight, timing set for best advance, wheel well covers in place, (absence of these will make your rig run hot as it changes the airflow from engineers design), ......right AFR not too lean, good dual exhaust flow.....no heat riser valve that can stick and heat up manifold,

coated headers, clean radiator fins, no under hood blanket, ( traps in heat).....everything helps...
 

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So do I need holes drilled if I'm running a Mr. Gasket high flow stat or maybe open them up more? I'm running a large tube two core aluminum radiator, flow cooler pump installed by Butler who I assume did the spacing correctly, a 16" 2600 cfm puller fan, a minimal half shroud...was having over heating issues when idling or moving slow so this winter I installed two 13" pusher fans for when I can't be moving also running about 80% water 20% antifreeze with two bottles of water wetter. Motor has 9.5 compression, iron heads and exhaust manifolds timing at 16° one step cooler plugs. Hopefully I'm good this summer but I'll take any suggestions that anyone thinks will help keep me cool.
 

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Lol. If I was having cooling issues, I would use them. Like Lemans Guy said, it's not One thing, it's all of the things.
 

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I would run 50/50 anti-freeze, but I don’t use water wetter...16 base timing is ok, but you can add 10 degrees from a vac can hooked to full manifold vac for even cooler idling. Unless that is 6 base and 10 from vac. 26 at idle will be fine, as long as you have no starter kick back or hard starting. But timing is another discussion.
 

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Rubber dams around shroud are required as well. Sometimes when we change to electric fans the original rubber shrouding that goes around the plastic shroud and under it are removed. Ames sells these kits so do other suppliers of rubber seals for doors and windows.

these rubber pieces make sure all air only goes then the radiator. They make a huge difference and of course fan blades half in and half out of shroud
 

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No vacuum advance on my MSD ready to run dist Butler doesn't like them they said, so is that a yes change to the 160 stat "and" drill the holes bigger ? Here's my shroud..I know I know...worthless but if I can get away with it I will.
142387
 

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I would change the thermostat, get a dizzy with vac advance!!! OMG, it'll add at least 10 degrees at idle! Usually. I don't have a shroud at all, so don't rely on that alone.
 

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Love Butler, they cut my short block. I live near them and they are great. But they really are building race engines. Racers do not need vacumn advance since they are operating with the pedal way down most of the time.

Street driving is very different and vacumn advance is most misunderstood. It allows you to add timing advance to burn the leaner mixtures at idle and light throttle cruise most efficiently and with better cooling and more power at lighter throttles.

Heavy and WOT are not effected because vacumn drops out. What whiz bang billet distributors with no vac advance give you is a racers set up. But you give up the advantages of 10 degrees more timing that you cannot get any other wat sans a computer.

Vac advance works from the load on your pedal and will transform your drivability and light throttle power and cooling without hurting any top end if set up correctly.

yes, calling that thing a shroud is generous. That is more like a goofy visor guys wear playing golf. That thing will do nothing.

yes I would drill the 3 small holes in thermostat, easy to do gives a little benefit. I would ditch the visor and get a real shroud with the proper or improvised rubber surround.

and I would put that whiz bang billet on eBay and get on of the MSD (if you like them) ready to run, or any Pontiac distributor that has vacumn advance and set it up right for 10 degrees of advance hooked to full manifold vac.
 

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I too, bought the MSD with no vac advance, and I returned it before installing it. Summit has a Pontiac Billet (made by MSD) with an adjustable vac can, adjustable mechanical advance, and an adjustable curve. I run a Mallory Highfire, so mine has no module in it, but if you dont run a 6AL or similar, then they have one with the module.

My base is 18 right now and with the can I'm getting 30. With 80 degrees and heavy humidity, the car idles in the direct sun at 190 degrees... However, Im still tweaking and tuning.
 
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