# Overheating fix?



## TommyG67 (Dec 17, 2009)

I recall reading somewhere about a "fix" for the well-known 400 overheating problem and I would like to know if someone has done this or can point me to some info.... 
The "fix" was to put a heater hose fitting in the driver's side head (just like the one on the passenger side); then run a hose around behind the distributor and "T" into "a heater hose" to improve coolant circulation in that head. I assume that the "T" would be into the heater hose running to the water pump, not the hose going from the passenger side head to the heater. 

Had I known prior to assembling/installing the engine, I would have drilled extra cooling passage holes in the head and block as I have since heard as a solution, but I'd like to avoid taking the heads off if possible. The operating theory seems to be that these Ponchos suffer from poor coolant circulation near the back of the head and this extra hose helps cure that. 

If anyone has experience with this or can point me to more info, I'd sure appreciate it! Oh, yeah.... all the water pump, thermostat, fan clutch, ignition timing, water-wetter, new radiator sorts of things have been tried, believe me! Fan/shroud placement is a possible contributor since I went to the 11 bolt water pump and the fan sits further forward, but I'd like to not get side-tracked on that just now - just gathering info on the extra coolant hose idea. :banghead:


----------



## nineteen 65 (Jul 8, 2013)

*Overheating*

Not sure if this would be of any help to you. I just broke in my newly rebuilt 389 engine in my 65 restoration. Originally engine ran at 220+, monitored on auto-meter temp gauge. The thought was that the engine was tight and with more miles the temps would start to head back down. Temps still remained high. The only modification that I made to the engine was lowering compression to 9.25:1 all else was stock along with re cored 4 core Harrison rad. It was only after I installed a shroud and with a few more miles the temperature settled down to 185-195 (Phoenix driving conditions). Not sure if you clearanced the divider plates. If they are new the clearance is too large and the water pump will cavitate and circulation will be poor.


----------



## geeteeohguy (Feb 2, 2008)

If all the engine components are operating as designed, there is no need for re-engineering the cooling system. These cars will run fine for decades and not run hot if: the tune is correct (timing and jetting), the water pump is the right one (cast impeller), the water pump divider plates are clearanced at 1/8" or thereabouts, the fan clutch is operational, the fan is the right one, the shroud is fitted properly, and the radiator is in good condition. I have driven hundreds of thousands of miles in these cars with stock cooling systems in the hottest environments without problems. With no modifications to the heads, etc.


----------



## the65gto (Oct 9, 2008)

nineteen 65 said:


> Not sure if this would be of any help to you. I just broke in my newly rebuilt 389 engine in my 65 restoration. Originally engine ran at 220+, monitored on auto-meter temp gauge. The thought was that the engine was tight and with more miles the temps would start to head back down. Temps still remained high. The only modification that I made to the engine was lowering compression to 9.25:1 all else was stock along with re cored 4 core Harrison rad. It was only after I installed a shroud and with a few more miles the temperature settled down to 185-195 (Phoenix driving conditions). Not sure if you clearanced the divider plates. If they are new the clearance is too large and the water pump will cavitate and circulation will be poor.


just curious?? What heads, originals? What brand of pistons/rods. Is you engine standard bore or?? how did you get the compression down. Tx


----------



## TommyG67 (Dec 17, 2009)

Heads are original "67" heads with mild port cleanup. I had a local )loco?) builder put the engine together (big mistake, I think - I usually do my own and will do so in the future). As a result all I know (or think I know...) is 0.030" overbore, dished pistons, Comp Cams XE256H cam. Resized original rods and pistons are unknown to me. I'm thinking of a pull-out & teardown to get things done the way I'd like :-(


----------



## TommyG67 (Dec 17, 2009)

Terrific! Happy for your success, but with literally 100's of "hits" when one types "GTO (or Pontiac) overheating" into a search, it's apparent that there is some sort of problem. A large percentage of those guys I know personally have cooling issues with these cars, as well. If the theory is true that rear cylinder head coolant flow is inadequate or marginal, then maybe the extra coolant flow holes drilled in prior to assembly or this external, after-the-fact idea might help? Trying to get some info on people with actual experience with that "fix".


----------



## geeteeohguy (Feb 2, 2008)

Not related to your overheating, but have you run a compression test? The Comp Cams XE series cams are meant to be used with low compression (<9CR) and used in conjuncton with 670 heads, would tend to build a ton of cylinder pressure early on which could lead to sever detonation issues. If you are using custom dished pistons, disregard. If you are using flat tops, be careful. My bet is that your cranking compression would be about 200-210 psi with your combo with flat top pistons. 175 is about the max for pump gas.


----------



## BearGFR (Aug 25, 2008)

Before you go spending money, pull the water pump and make sure the clearance between the impeller and the divider plate is right. That one item can have a dramatic effect on cooling. There are several threads here talking about it.

Bear


----------



## TommyG67 (Dec 17, 2009)

Thanks for replies -
The engine build was done with dished pistons - the idea of cam & pistons was a pump-gas friendly engine with good torque. I was trying (very hard) to get this car ready for the Nationals in Colorado (2012) and had the engine redone by a (supposedly) experienced Pontiac engine builder. I usually have built my own engines and plan to do so in the future, as I am not thrilled with the performance, either - even if it did not run too hot. The overheating may or may not be a build issue, so I don't want to dump on the engine shop, as I truly do not know what's wrong.

We went through the water pump clearance thing to no avail - ended up trying a FlowKooler which helped some. I have written up a fairly detailed history of what has been done to the car and what the results were, but did not think anyone would want to wade through all that on the forum. If you care to take the time, please see attached.


----------



## chuckha62 (Apr 5, 2010)

Quick question... 

Your fan clutch. Is it a good quality Hayden, or other OEM equivalent? ...or is it a cheap Autozone/PepBoys/O'Reilley's brand?

They are not all created equal. I was discussing this issue with a local radiator shop owner (not many around anymore) and he said "Oh, it's your fan clutch." and he was right. He went on to say that in his experience, the new off shore built clutches were not the same as a good American made product and that he sees it all the time. His contention is that the viscous material used in some clutches is not the same and it doesn't exhibit the same consistent lock/unlock characteristics as the better American made clutches.

Just a thought...

Chuck


----------



## Jared (Apr 19, 2013)

What do you consider as overheating? Are you basing this on a temp gauge reading or is the car actually boiling over. On a hot day (90F or up) mine runs at about 220 or so. On a cooler day that is 80F or lower, it runs at about 195. I thought it was a bit hot until I looked into it. From what others have said in previous posts, this may not be unusual or too hot.

That being said, if you are boiling over, you definitely have a problem.


----------



## geeteeohguy (Feb 2, 2008)

Your fan is too far into the shroud. This can actually cause turbulence issues and hotter running. Probably not the issue, but something to look at. What's the temp reading when it's spitting out coolant?


----------



## TommyG67 (Dec 17, 2009)

*Really overheating - Oh Yeah!*

Fan clutch is extra heavy duty Hayden 4797 - very "stiff" and seems to pull a LOT of air.

As regards question of "what do I think is overheating" - it boils over, no doubt. Mechanical temp gauge was stove-top checked up to ~210 degF and was spot-on. Temp readings on engine confirmed with temp gun at t-stat housing near temp gauge location. Engine is bubbling over at 230-235 indicated, at which time I shut down. Outside temp is not a huge factor - it gets up there quicker on a 100 degree day than a 70 degree day, but it still gets there. Increased power demand nudges temp up quicker with slow to no recovery as I drive. Even when it's 60 degrees out, if I drive it 1/2 hour or so, it will be up to 220-230 and climbing.

I wonder if anyone out there has done the 11 bolt water pump conversion and noticed that the ~3/4" longer assembly (which pushes the fan further into shroud) has caused an issue? Maybe I should convert back to 8 bolt setup to back the fan out?

I also wonder if anyone out there has gone to a 200R4 trans and noticed a change in engine goemetry - I do not recall the fan being tilted as it is now prior to the trans change. Also I wonder if the 200R4 generates more heat?


----------



## geeteeohguy (Feb 2, 2008)

Your engine is generating so much heat that it won't cool down when driving at speed or with the fan pulling air. It can not give up the heat it produces. Water pump or radiator, or both. You may need to go to a much bigger radiator. Something is wrong here...usually, a car will run hot in town or on the highway, not both. SInce yours just keeps building more heat no matter what, it is unable to shed the heat with its current cooling system. Good luck, and keep us posted.


----------

