[psw]

I finally solved my chronic overheating problem and wanted to share my case with the forum. The car is a '66 GTO hardtop coupe originally with the tri-power 389 (absent from the car when I bought it), but for the last 15 years or so, with a 1971 0.060-over 455 block and 6x heads running around 9.75:1 CR. The car has a TH-350 automatic and 3.55 gears, an Edelbrock P4B manifold, an 800 cfm Edelbrock AVS carb, a Comp Magnum 280 cam and headers. At the time of the engine install, a new OEM-style 4-core "desert cooler" radiator from Ames was installed along with a new fan and thermal clutch. This radiator was a stock replacement, except for the upgrade from 3- to 4-row on this non-A/C car.

Despite the new radiator, overheating was chronic after the 455 installation, typically occurring on hot summer days in traffic, but it would run cooler in the winter. Like many on the forum, I would nervously drive the car, habitually watching the temperature gauge and just plain avoided driving the car in traffic during the summer.

Over time, I tried virtually all the ideas discussed in this forum: added a shroud, a Flowkooler water pump, new properly clearanced divider plates, high-flow thermostat, water-wetter, a transmission cooler, made sure the air/fuel ratio and the vacuum advance was correct, blocked off the exhaust cross-overs (we are in Texas) etc, etc. None of this solved the overheating problem on the hottest days, where the water temperature would slowly increase up to 220-230 (or more) in traffic, and would run over 210 on the highway. In the winter, the car would stay at around 200 in traffic, but would still run around 210 on the highway (say around 3000 RPM).

The extremely hot weather this summer finally motivated me to try a Griffin aluminum radiator rated for use with up to 600 HP, which finally solved the overheating problem. It really has been hotter then ever here in Texas with weeks of 100+ days already. The car now runs consistently at 180 (w/ a 180 t-stat) in traffic, on the highway, and can idle indefinitely without getting hotter than 180. Needless to say, it is so wonderful to finally have the overheating problem done with.

My conclusion is that a somewhat worked 455 can not be sufficiently cooled in Texas heat with an OEM-type and capacity radiator originally designed for a 389, even when all the other aspects of the cooling system and engine tune are right.

[david400]

Glad you resolved your problem , Have you run it on the freeway for over 30 minutes yet ?

[Pontirag]

so what makes the griffin work...other than its aluminium. does it hold more volume of water than the factory radiator?

[bryansMtngto]

that was 1 of the first things I changed years ago when i put my first built motor in my GTO been running an Afco aluminum for atleast 15 years now. never have had an overheat issue, even when makeing over 600 hp and spraying.. Aluminum radaitors are well worth the investment IMO

[psw]

Originally Posted by Pontirag

so what makes the griffin work...other than its aluminium. does it hold more volume of water than the factory radiator?

Of the several aluminum radiators on the market, Griffin was the first one that I came across that offered OEM size and fit, and also rated their radiators for different horse power levels. This does make perfect sense. The amount of waste heat an engine produces is directly proportional to the amount of power that it makes and its overall efficiency, hence you are able to choose the radiator that physically fits your application and your HP level, and still looks pretty much stock, if it is painted.

My understanding is that as you go up in power-level, their radiators simply have increased cooling capacity. I am not sure if they achieve this via increased water volume, increased heat transfer area, more fins, more rows, etc. To me, the kicker was I could size the radiator relative to my power output. For my application they offered 400 and 600 HP radiators, for essentially the same $$.

[psw]

Originally Posted by david400

Glad you resolved your problem , Have you run it on the freeway for over 30 minutes yet ?

I have not tried it out on a long freeway drive yet, but I will report once I do.

[69Goat1]

I have a .035 over 455 with 87cc E-heads and a small solid roller making a touch over 600 HP (estimate: 3525 lb car ran 10.28 @ 130 with it) and I have a 3 core copper/brass radiator in it our of a mid 80's G-body and a PRW aluminum stock replacement waterpump and we have been having those weeks of 100+ days as well and I have yet to get over 190 degrees with it. I have 3.73 gears and have driven it 70 miles one way at 70-75 MPH...

[SD421]

My problem has always been air getting trapped in the system after I had refilled the water/anti-freeze. I would fill up the radiator until full then leave the radiator cap off and then start the engine. When the thermostat had openend, Id go and look into the radiator and sure enough all the water was "gone". Id just fill it up with more water until it was near the top of the lip then put the radiator cap back on. Be sure its the correct pressure for the cap. It would run at 180 degrees with a 180 thermostat.
-Don

[psw]

Originally Posted by 69Goat1

I have a .035 over 455 with 87cc E-heads and a small solid roller making a touch over 600 HP (estimate: 3525 lb car ran 10.28 @ 130 with it) and I have a 3 core copper/brass radiator in it our of a mid 80's G-body and a PRW aluminum stock replacement waterpump and we have been having those weeks of 100+ days as well and I have yet to get over 190 degrees with it. I have 3.73 gears and have driven it 70 miles one way at 70-75 MPH...

Sounds good, but I am still wondering if a stock 1966 GTO non-A/C radiator (or equivalent stock replacement), originally designed to cool a 360 HP 389 can properly cool a mildly-built iron-head 455, with likely an extra hundred or more HP than the original 389?

[psw]

Originally Posted by SD421

My problem has always been air getting trapped in the system after I had refilled the water/anti-freeze. I would fill up the radiator until full then leave the radiator cap off and then start the engine. When the thermostat had openend, Id go and look into the radiator and sure enough all the water was "gone". Id just fill it up with more water until it was near the top of the lip then put the radiator cap back on. Be sure its the correct pressure for the cap. It would run at 180 degrees with a 180 thermostat.
-Don

I have had this problem, too, but the chronic overheating problem I described in the original post was occurring with a full system, no trapped air and with a new 15 psi cap.

[Pontirag]

not trying to pick a fight but: an interview with an aluminium radiator manufacturer in hemings muscle care magazine stated that al things being equal between an aluminium and a copper/brass radiator theres no difference in heat transfer.


and there being little difference between the raiator used in say, for example, a 70 lemans 350 radiator, a gto 400 radiator and an optional 455 radiator. and there is very little difference in fluid volume/capacity between the smallest six cylinder radiator and the largest heavy duty radiator.

these two considerations would suggest that there was something else other than the aluminium materieals that make a difference.

but I think it might theoreticaly answer your question about weather a 389 system can handle a 455 engine

[psw]

Originally Posted by Pontirag

not trying to pick a fight but: an interview with an aluminium radiator manufacturer in hemings muscle care magazine stated that al things being equal between an aluminium and a copper/brass radiator theres no difference in heat transfer.


and there being little difference between the raiator used in say, for example, a 70 lemans 350 radiator, a gto 400 radiator and an optional 455 radiator. and there is very little difference in fluid volume/capacity between the smallest six cylinder radiator and the largest heavy duty radiator.

these two considerations would suggest that there was something else other than the aluminium materieals that make a difference.

but I think it might theoreticaly answer your question about weather a 389 system can handle a 455 engine

I understand, no fight here, and I am not trying to be an advocate for the use of aluminum as a radiator material. I have also followed the discussions about the thermal properties of the various metals used in radiators. I am just basically trying to understand why I did virtually everything discussed on this forum, except the use of an electric fan, and could not get my mildly-build 455-powered 66 GTO to run cool with a stock-replacement (non-A/C) radiator. The last thing I did was to trade out that stock replacement radiator for one that was designed and sold as being able to handle 600 HP and bingo, problem solved. It happened to be aluminum, but that is not really my point. I am wondering if there are other people who have cool-running mildly-built iron head 455s that are using stock non-A/C 1966-type radiators. If these radiators are commonly used to successfully cool such cars, then I suppose my conclusion should be that the particular stock replacement radiator that I happen to get was somehow defective.

[ERIC AULL]

I am glad to hear the Griffin sucsess story! I bought one for up to 800HP...Aluminum with (2) 1.5 inch rows.....I figure, why not, I never heard of a Pontiac running "too cool"!

[Pontirag]

pontiacs are notoriously cool


what are the dimensions of the griffin 600 hp radiator and what about its design is different than the factory one

and Eric AUll what about your 800hp radiator?


I got a 65 lemon with a hd ac radiator set up, will the Griffins fit in the factory location and do they appear oigional?

[psw]

Originally Posted by Pontirag

pontiacs are notoriously cool

what are the dimensions of the griffin 600 hp radiator and what about its design is different than the factory one

and Eric AUll what about your 800hp radiator?

I got a 65 lemon with a hd ac radiator set up, will the Griffins fit in the factory location and do they appear oigional?

OK, here is a comparison of radiator dimensions and construction from the various catalogs arranged in order of as-advertised increased cooling level. All of the following are for a 1966 A/T GTO without A/C. All of these are sold as direct fit, bolt-in replacements that will accept the stock shroud. All have stock-looking top and bottom tanks and are of the down-flow type. Since the dimensions are somewhat different, I also calculated the "effective volume" of each radiator. As discussed earlier in this post, I implemented virtually all the other suggestions in this forum trying to solve my chronic overheating problems, which was finally achieved by replacing #2 below with #4. Since the engine causing this overheating is significantly larger and more powerful than the original tri-power 389 (as discussed in earlier posts in this thread) I have hypothesized that the stock-replacement radiator is unable to handle this extra load. As shown below, there are significant differences in the various radiators:

-----Radiator Type-------------------------------Dimensions-(in.)---------Volume (c.i.)
1. original OEM style brass/copper, 3-row---: 15.625 x 24.75 x 2.000 = 773
2. brass/copper, 4-row "desert cooler"------: 15.625 x 23.75 x 2.625 = 974
3. Griffin alum 2-row, rated for up to 400HP: 15.000 x 25.50 x 2.250 = 861
4. Griffin alum 2-row, rated for up to 600HP: 15.000 x 25.50 x 2.750 = 1052
5. Griffin alum 2-row, rated for up to 800HP: 15.000 x 25.50 x 3.250 = 1243

Additional note from the catalogs: No.2 has larger tanks than No.1.

Additional observations from the two radiators in my possession.
No. 2 has 42 down tubes and 12-13 fins per inch between the tubes.
No. 4 has 64 down tubes and 15-16 fins per inch between the tubes.

The photos below show No.4 as installed, and it was indeed a direct fit bolt in replacement. I could not wait for the paint to arrive, so I installed it before painting it, but I do plan to paint it black. The last image shows how the down tubes in both the OEM-type and the Griffin-type are arranged. (I tried but could not get good photos...) The figure is not exactly to scale but there are more tubes per inch in the Griffin, as indicated. The OEM uses four rows of relatively smaller tubes, whereas the Griffin uses two rows of relatively longer tubes. All three HP levels associated with the Griffin are achieved with two rows, as in the figure below, but by using 1", 1.25" and 1.5" length tubes, corresponding to the increased radiator thicknesses shown in the table above.

I am still waiting to hear if there are any forum members who have mildly built 455s (not low-compression 455s) running cool with stock 389 radiators. If so, great, it might be that the stock replacement radiator that I bought (No. 2 above) was somehow defective.

[bryansMtngto]

Here's a interesting acticle on why aluminum radiators work better the Brass.I'm assuming most radiator companies use same tech and or design.
http://flex-a-lite-blog.com/2010/03/...inum-vs-brass/

[geeteeohguy]

I ran my '65 GTO from 1982 to 1987 with the stock 4 row Harrison tripower spec radiator in it with a .030" over 428 with a hot cam and headers. Never had overheating issues. Since '87, I've run a .030" 389 in this car with a hot cam and headers, and still no issues. Recently, I added a fan shroud and it dropped the temps about 15 degrees to the 180-190 mark. Previously, both engines ran 195-205 and did not overheat. I agree more horsepower and more compression (and more cubes) will produce more heat, though. From personal experience, all of the components in the cooling system need to be up to snuff: water pump, water pump clearance, divider plates, fan, fan clutch, thermostat, radiator, and radiator cap. A fan shroud always seems to help, too. I have friends who have run built 455's with the stock radiators successfully...this was long before all the trick aftermarket stuff was available.

[ERIC AULL]

WOW PSW, Thanks for the charts and pics and info!! Eric

[psw]

Originally Posted by geeteeohguy

I ran my '65 GTO from 1982 to 1987 with the stock 4 row Harrison tripower spec radiator in it with a .030" over 428 with a hot cam and headers. Never had overheating issues. Since '87, I've run a .030" 389 in this car with a hot cam and headers, and still no issues. Recently, I added a fan shroud and it dropped the temps about 15 degrees to the 180-190 mark. Previously, both engines ran 195-205 and did not overheat. I agree more horsepower and more compression (and more cubes) will produce more heat, though. From personal experience, all of the components in the cooling system need to be up to snuff: water pump, water pump clearance, divider plates, fan, fan clutch, thermostat, radiator, and radiator cap. A fan shroud always seems to help, too. I have friends who have run built 455's with the stock radiators successfully...this was long before all the trick aftermarket stuff was available.

When I first got the car in 1983, it had a very tired 400 ci 360 HP engine from a 68 GTO with a 3-row Harrison with no fan shroud, and it ran cooler than the fresh 455 that was later installed along with the new 4-row brass/copper "desert cooler" described earlier in this post.

[psw]

Originally Posted by ERIC AULL

WOW PSW, Thanks for the charts and pics and info!! Eric

I have been silently lurking through the posts for some time now, reaping all the great advice available herein. It was finally time I could add something constructive, so my pleasure!