[67Fbird]

Ok I am willing to do this on my 455 build as I ALWAYS had cooling issues on my last 400 build....25 yrs worth. The 400 was iron headed .030 over TRW slugs, RAIV cam and headers at 10.2:1 compression. The only way I kept cooling "reasonable" was running the CARB a little fat. 4 row MODINE radiator every fan know to man kind, shrouds, waterpumps, pulley sizes...you name it NOPE. When I say reasonably cool I mean on a 90* day it ran at 210 idle in gear in traffic. Yes It would go do to 195* driving (160 thermostat) but I was at the mercy of the temp gauge (yes 10000% calibrated). When I went EFI in '08 even the ECU (its own sender) confirmed the dash gauge setting.

So can I get some clarification on this mod.?

https://forums.maxperformanceinc.com...d.php?t=583733

here it shows what gets plugged and the 1 new hole in the block. (post 5) pic shows plugging the water holes in EXHAUST SIDE of block around forward most cylinder (1 or 2) then plugging the INTAKE side water hole toward FRONT between 3 and 5 (4 and 6) of cylinder.

So basically we are MAKING the water go from the FRONT of block toward REAR and the first time it is allowed to enter the head is thru the NEW hole between 3-5 (4-6) and of course all holes reward of that. This allows it to NOT "short circulate" around the front cylinder only?

Am I understanding this correctly? I would LOVE to be in control of water temp and not at the mercy of my ingenuity.

[Mike Davis]

I always add the hole in the block deck between 3/5 and 4/6. Called the 421 mod. I have plugged the deck and drilled a smaller hole 1/4 in the plugs but did not notice a big difference with the plugs. I did notice a difference with the block being drilled.

[AIR RAM]

Its possible that your system is just not able to keep the temps down to 160... so when the temps reach 160, the T-stat just stays open... when that happens coolant does not stay in the radiator long enough to drop down to that 160 T-stat .... so you basically have a run away cooling system.

I would try a 180T-stat and see if that doesn't keep the temps down.

In the end, you need to stop the flow of coolant long enough for the radiator to do its job. That 160Tstat is like having no t-stat at all.

Another great mod you may want to try is turing your aluminum single pass radiator into a tri-pass radiator... those are known to drop temps 15-20 degrees...

SPEED SAFE, NICK

[lust4speed]

If Pontiac engineers decided that the 421 cooling holes shouldn't be drilled, it's probably a safe bet that they made that decision through rigorous testing. Figure that a machine drilled all the holes at one time in the deck and it didn't matter to Pontiac whether that additional hole was drilled or not, but for some reason they stopped drilling those holes.

Aggressive coolant flow decreases hot spots in the block and heads which is a good thing. If the coolant is flowing twice as quick it would pass through the radiator twice in the same amount of time. Coolant staying in the engine twice as long is going to get twice as hot so no gain in letting it stay longer in the radiator.

I live about 60 miles from Palm Springs and several of our members live in the Palm Springs area. We have found through testing that no thermostat and a properly working thermostat both will produce maximum cooling. Basically the internal restriction of the engine is the limiting factor on coolant flow and even if the Chevy myth of needing a restriction in the system is true for some Chevy's, we have found that it is definitely not true for Pontiacs.

[steve25]

Pontiac stopped drilling those added center block deck cooling holes because the newly designed timing cover with its two Round seals and baffle was far more efficient then the one used into 1966.

These so called cooling holes where not to help the whole motor to run cooler, be just the high heat center Exh port area and as such reduce the head gasket burn out issue they would have.


If you motors water pump and cooling system can hold a good temp in terms of hanging near your choose T stat temp when at speeds above 30 mph, but can't do so at idle conditions then you have one of two, or a combination of two problems.

Either your not moving enough coolant at idle, and or your not moving enough air at idle!

[chuckies76ta]

Originally Posted by AIR RAM

Its possible that your system is just not able to keep the temps down to 160... so when the temps reach 160, the T-stat just stays open... when that happens coolant does not stay in the radiator long enough to drop down to that 160 T-stat .... so you basically have a run away cooling system.

I would try a 180T-stat and see if that doesn't keep the temps down.

In the end, you need to stop the flow of coolant long enough for the radiator to do its job. That 160Tstat is like having no t-stat at all.

Another great mod you may want to try is turing your aluminum single pass radiator into a tri-pass radiator... those are known to drop temps 15-20 degrees...

SPEED SAFE, NICK

All I've ever run is 160 degree thermostats in every built Pontiac engine. Have never had to date an issue with over heating. We just removed a 468 and replaced with an 505 IA2, same radiator and still no issues with a 160 thermostat. Just changed to an electric water pump so no data yet on that.



How does going from a 160 deg stat to a 180deg stat change anything except raising the coolant temperature.? Once the stat opens it still gonna flow the same amount of coolant. It's not gonna slow the coolant flow down in my opinion.



I do understand what your saying about the coolant staying in the rad long enough to remove heat. But the coolant has to travel from the top of the rad to the bottom before entering the engine again. I guess one could experiment with water pump pulley size and see what happens. I've always run the smaller water pump pulley with great success. Just saying.

[67Fbird]

Just looking for something I have not tried. Basically I have used a stock thermal fan, straight fan BIG FAT flex fan all with a shroud fan 1/2 way in...all the way in, all the way out. Electric fan + FORD MARK VIII 2 speed (closest thing to actually controlling it) a couple other e-fan combo's...moot. Stock pump (cast impeller) a flow-cooler pump both with separator plate re-formed (not just hammered....I am a tool & Die maker ) to .030-.040 clearance with gasket. Then we get to the pulleys. I MADE my serpentine belt drive by adapting 6 groove pulleys from the junk yard. I have 4 water pump pulleys I have made. 1-1 (relative to crank pulley size) 100% 10% UNDERDRIVE, 10% OVERDRIVE, 30% OVERDRIVE. Considering I was NOT sure what my original pulleys were as I had MANY laying around when I built the original v-belt set. I am not sure WHAT sizes PONTIAC put on a 1968 400 with AC. Also have used Wetter-water (good stuff...just not for winter) Alcohol and dishsoap. Radiator was a 2-row OEM then went 4 row MODINE. It flows like the garden hose wide open, been cleaned, checked...etc (NOT ALUMINUM ).

I would like SOME clue as to what ELSE I might be able to do as the LAST thing I need is having to fight cooling with this motor.

NOW...this is a 81 TA with a 77 nose so frontal area is ....NOT MUCH.

Could it be????
AFR? I shoot for a 12.3 Idle and 11.2-11.5 WOT (injected ..of course) when it was a carb...read the plugs/twist the screws 1/2 PAST best vacuum (rich)
Timing/ignition: MSD 6a box via hei dizzy with MSD PRO POWER coil...initial about 14-16 with total about 32. all in by 2800. Never got to doing the timing curve per the ECU (was still trying to program the fuel maps (pre-self learning stuff here)

[PAUL K]

Originally Posted by lust4speed

If Pontiac engineers decided that the 421 cooling holes shouldn't be drilled, it's probably a safe bet that they made that decision through rigorous testing. Figure that a machine drilled all the holes at one time in the deck and it didn't matter to Pontiac whether that additional hole was drilled or not, but for some reason they stopped drilling those holes.

Aggressive coolant flow decreases hot spots in the block and heads which is a good thing. If the coolant is flowing twice as quick it would pass through the radiator twice in the same amount of time. Coolant staying in the engine twice as long is going to get twice as hot so no gain in letting it stay longer in the radiator.

I live about 60 miles from Palm Springs and several of our members live in the Palm Springs area. We have found through testing that no thermostat and a properly working thermostat both will produce maximum cooling. Basically the internal restriction of the engine is the limiting factor on coolant flow and even if the Chevy myth of needing a restriction in the system is true for some Chevy's, we have found that it is definitely not true for Pontiacs.

Good post,thanks!

Do you have any tips that will help our Pontiacs stay cool?

[Sirrotica]

I've been down this road before, I had a very good radiator repair man in my hometown that I discussed this problem with.

The heat rejection from the radiator into the air, and the heat rejection from the block into the cooling system happens at the speed of electricity, as from my understanding is done by electrons. The speed of the water being pumped through the system doesn't even come close to the speed of electricity, so if you take that as a given in physics, you can quit worrying about how fast water cycles through the system.

My problem was running a 400, and a 428 inch ( the 67 GTO, and the 69 GP in my signature pics) engine on a dirt track, and during a race the temp would creep up and by the end of the race it would either overheat, or be near overheating. I've also had friends that have run Pontiac dirt cars with the exact same problems.

The restrictor with or without, made little difference, however not running a restrictor/thermostat drops pressure in the block. Pressure internally does stop hot spots from happening and turning the coolant to steam. Once it turns to steam, the cooling slowly deteriorates. Keeping pressure in the block by use of a restrictor/thermostat should help the problem, but in my case it didn't help enough.

The radiator man tried to help me with all the tricks he knew that worked, but none of the suggestions that I tried stopped the problem. The last suggestion that did work was to add more coolant capacity to the system. I was running the GP at the time with the 428.

Because the GP front end has tons of room I added another radiator, I had 2 3 core radiators back to back, that solved the problem. The car never overheated again. A friend had a 455 Firebird dirt car that had the same problem, he added another 3 core to his car and stopped the problem too.

The radiator man suggested a 1 gallon can with nipples soldered in each end to increase the capacity. The can would be mounted so that it was inline in either radiator hose. I however had the room in a race car to add another radiator, as did my friend with the Firebird. I figured an extra radiator would help 2 fold by rejecting more heat, along with increasing the cooling system capacity. It worked flawlessly. You couldn't make either of those cars overheat after adding the second radiator.

I have never made up a gallon can as he suggested, and plumbed it in, but from my experience if I had a street car I would definitely try it. I have had numerous Pontiac street cars that were near overheat on really hot days, so this problem is quite frequent among Pontiac cars.

I'm old enough to have worked on these cars when they were fairly new. I actually did my Vocational auto mechanics Co Op time in a Pontiac dealership in 1970. My father was also a mechanic. He drove mostly Pontiacs all of his life, along with working at the local Pontiac dealership. The overheat problems were not just in the Stratostreak V8s, from what my father told me. He also said the flathead 6 and 8 cylinder cars were always tough to keep cool too. Maybe an inherent engineering flaw....

I do believe that Pontiacs have a lower percentage of safety margin engineered into their cooling systems. If everything isn't 100% right you run into problems. You also have a slow deterioration of components over time that can eat into that safety margin. I also believe certain blocks aren't the same internally as ones that seem to have no overheating problems, just abnormalities in casting process. Being around them most of my adult life, and racing them, as well as using them in high performance applications leads me to this belief.

One other suggestion I have seen make a slow overheat problem in an automatic equipped reach boom forklift with a Detroit Diesel. If you have an automatic transmission, and the cooling lines are plumbed through the radiator tank, The extra load on the cooling system placed on it by the transmission fluid will run the coolant temp up slowly, especially at idle in gear.

I worked on this forklift with the factory engineers for nearly 2 years on a overheat problem. They tried larger radiators, reversing the fan so it pushed outside air over the radiator. I told the engineers that I was convinced that the transmission fluid was causing the coolant for the engine to overheat early on. They of course ignored my suggestion, because I didn't own a piece of sheepskin on my wall. Turns out that separating the transmission fluid into its own separate cooler with electric fans stopped the overheating completely. Maybe I'm not as dumb as they thought I was........

One engineer did tell me that according to his calculations, there was a 12% safety margin engineered into the cooling system.... To me, 12% could be taken away by dirt, and debris in the cooling fins. This machine was being used in a sawmill, so there was constantly sawdust around this machine. If Pontiac engineers used that 12% figure when engineering their cooling systems, it could easily be overcome with some flaw in one part of the system, just my thoughts. I believe once you stretch that margin out, you'll make up for the flaw you could have.

My , take it for what it is worth......I hope some of my ramblings can help you out.

[Formulajones]

If everything is right, there shouldn't be cooling issues, providing you have a radiator capable of keeping up. All a thermostat rating does is force the engine to run at that temp, if the cooling system can't keep up, it runs warmer, but it won't run colder than the rated thermostat temp.

I haven't done anything fancy with dad's GTO as he's upgraded engines over the years. He ran a 4 core brass radiator in it for decades with 400's-455's, and even with the current 571. Using the stock shroud, a HD 7 blade clutch fan, the brass radiator still kept the 571 cool. It's always had a 160 stat in it.

More than a year ago he decided to upgrade to an aluminum radiator from Cold Case. That made a noticeable difference in how well it controls and maintains the temp with much smaller swings. Everything else has stayed the same. Basically, idling you just can't get it hot, that's when it runs it's coldest. Anything putting around town at 2000 rpm down to idling it just doesn't run above 165 degrees in the Arizona summer heat. On the highway buzzing along at 3,000 rpm it creeps up to about 185 or so, if you slow down a pinch, the temp comes down a pinch. As soon as you roll off an exit ramp and idle, the temps come back to the 165 range within a couple minutes.

Can't complain about that with an engine making over 700hp on pump gas, and it's just a basic stock cooling system with a nice radiator. I don't check water pump clearances or any of that stuff, no fancy tricks.

Most of the time when an engine has a heating issue I find it's more timing related. That seems to have the most affect on it rather than all the other little tricks people do. Vacuum advance is a biggy and really should be operational with a proper curve that compliments the engine.