I first want to disclaim I am only 17 years old and am still learning a lot about cars. However, to the subject at hand, my dad has told me countless times one day I will inherit his 1969 400 Firebird. The car has had many issues regarding overheating and he has about given up, but I refuse to let it sit in the garage without at least trying. I have been with him or have been told about all the things he has tried including everything thermostat related(it has a 180 right now). The engine at idle jumps to around 225 after sitting 10min and while driving it gets to 250 but doesn't boil over even with the heater on(you can hear the engine tick). He even put an aluminium radiator from giffenrad.com and paid a little much for it. It has a new MSD distributor and the car shuts down at times for what is highly likely that the coil gets cooked because it's not heat protcted. I was even told at times the rubber pieces behind the water pump not being installed may be a cause but they are. My dad seems to think it may be over bored but I doubt it can cause the car to heat up as fast as it is. If you need any pictures I can take a galley when I get home but of I get a list together of suggestions it can really help. Thanks!

Just a couple of thoughts on your problem, you may have one or many problems, So I will name a few to help the best I can, If you have changed the Radiator, water pump, and the plates and seals inside with upgraded ones, you may want to start next by Jetting up your Carburetor, todays fuel is not made for Carbureted Cars, everything is Fuel Injected now, a Lean condition will cause your car to run hot, if that's not the case, then you may want to switch out your Distributor to a Mechanical Advance MSD drop in unit, set your total timing to 36deg at about 2500 RPM, again timing can cause your engine to run hot, something else to look at, you may have a crack someplace in the heads or block, maybe even a blown head gasket causing a problem, allowing compression gas to enter into the water jackets causing it to heat up quickly, that one I had first hand on a 350, would heat up in 15min, coolant smelled bad and had some black stuff floating in it and with the engine running, cap off the radiator bubbles were seen coming out easy way to tell, was not letting water into the oil, or using water, but just allowing compression gas into the water jackets, if that is the problem, make sure to flush the block out along with the radiator, sediment in your water jackets could be a problem also not allowing the coolant to flow around the cylinders enough to remove the heat, check your Fan make sure it is on right, and if you have a clutch fan make sure that it is working right, make sure you have your fan shroud on, a must for sure, Pontiacs tend to run warm as it is, a shroud makes all the difference. If I can think of anything else I will post more.

There are 3 critical things to check/verify.

- Water pump; this is the most critical, many of the replacement pumps do not maintain the close tolerances of the OEM pump. The intermediate plate to impeller gap should be minimized to improve flow. also the donut seals must compress and make contact with the plate - this area often corrodes.

- Timing; with today's lower octane fuel, timing is often set lower to avoid pinging. If timing is retarded too much, the engine will run hot. The options are running higher octane fuel [additive] or reducing the compression by changing the cylinder heads.
re fuel; there is no special blend for NA engines vs. FI engines. Back in the 60's fuel contained lead for lubrication and had a higher octane rating.
Auto manufactures designed engines to run with 95-98 fuel which is sadly not available anymore.

- Coolant; As with most cars, a 50/50 blend works best.

Good luck..

in a non AC car 30-70 % mix is best....(30 coolant, 70 water) 50/50 best for ac units...

Nick,

Go through my list:
https://firstgenfirebird.org/forums/ubbth...true#Post300965

I would work through the list and eliminate what you can one at a time.

I had a very similar situation with my 67. The car was fine when it was moving, but if I sat still all hell broke loose. I tried a ton of things. 4 core radiator, different thermostats, messing with the timing, assorted deities, and for me it turned out to be mostly the water pump diverter plates.

basically Pontiac made water pumps with large impellors that would spin really close to the diverter plates and create a good bit of suction to move the coolant around even at low RPM. Unfortunately, a lot of aftermarket water pumps have much smaller impellors and the gap between the diverter plate and impellors is too great to move adequate coolant when RPMs are low. For me I just bought new diverter plates ( I think there are 2 plates on 67's, your may be different like the one pictured in the link below) and then popped a new water pump on. I checked the clearance and hooked everything back up. It made a horrible screaming noise since I had it too close, so I took it apart again and adjusted a bit, and then it fit fine. Now she runs much better. If your using an aftermarket water pump, I would wager this is like 80-90% of the problem. Follow this link for a better idea of what I'm talking about.

http://www.wallaceracing.com/water-pump-mods.php

Be sure to rub it in your old mans face when you are cruising at a nice cool 180oF.

I'll have to look that up - I've never heard of that...

just chemistry for best cooling....but AC needs more "coolant"..

I have never seen an overheating problem fixed because of correct mixture of coolant and water.

If you have more water than coolant the effective boiling point is at a lower temperature. I once attempted to run 2/3 water to 1/3 coolant and the system started to boil after moderate driving. At the extreme, if you ran 100% water, the system would boil over relatively quickly.

That sounds reasonable but a few random thoughts come to mind.

heat transfer function through the radiator wall from liquid to air is similar regardless (almost) of what fluid is inside the radiator

pressure keeps water from boiling. I have ran vehicles many times on strait water and never had boiling over issues. I don't know much about pressure ranges for radiator caps.

Just did some internet digging and running strait water is more efficient then running strait coolant. Coolant is just for anti corrosion and of course keep the water from freezing.

Just my $0.02. Adding coolent adds viscosity which promptes laminar flow through the cooling sys. versus turbid flow with straight H2O which has limited heat transfer/exchange due to residence time, but too much coolent limits the heat transfer. I mix 60:40 just in case but the car is stored in an environment that will see below 30 degrees but never had a problem with over heating since a radiator recore when purchased in 2012.

Kevin-