[kb8n]

I have recently rebuilt a pontiac 400 for a friends 67 gto. We got the engine fired up day before yesterday and after about ten minutes into the breakin the temp climbed rapidly. We let it cool for awhile added some more fluid then restarted and 5 minutes into that it pushed water out of the radiator.
We have checked the plate to vane spacing on the pump (8 bolt w/two plates in timing cover) and we have excellent flow in the radiator. The block was hot tanked so that has to be clean. Radiator condition is ok it ran with it before the rebuild. We are going to replace the fan clutch tomorrow night and try again.
The radiator has the fan guard and no fan shroud, No A/C the trans is manual so no cooler in radiator. I set the timing at 10 BTDC, Cam is a small comp cams nothing major. (same cam as was init before the rebuild).
He did say that sometimes with the old motor it seemed to be running hot (No Gauges in car) he was going by smell and feeling underhood temps, it would not push water out the cap but did push alittle out of the overflow tube a couple times.
Thermostat actually stuck open on the first run of the motor we replaced it tonight with another 180 (Idrilled two 1/8th inch holes in it as some said they did on here) filled the upper hose with water as much as possable before placing it back on the radiator, after all hoses were attached and radiator filled to within 1/2 inch of the cap throat (left a little room for expansion). I bled the heater hose and it sure seems like any air pockets should be worked out by now. Ran it tonight and again will keep getting hotter as long as it idles (2000 2500 rpm approximately) will heat up faster if I lower the rpms but I am still trying to fluctuate RPMs for cam breakin but this is hard to do with only being able to run it for ten-15 minutes.
Sorry for long post but any ideas would be appreciated, thanks in advance.

[stockcar32]

You might want to put a temp gauge in it, I know I would if it was my new motor. Try replacing the radiator cap, sometimes they go bad.You may not be overheating, just pushing out the water because of a bad cap.
I hope this helps,
Tony

[kb8n]

Oh, I should have mentioned I do have oil pressure and water temp gauges hooked up for the breakin. I just could not fire it up without them. The temp will climb to 230 + but I shut her down when it gets close to the 230 makes me nervous. But thanks for the reply.

[kb8n]

Well the new fan clutch helped it will run for 25-30 minutes before getting to 225-230. Then after we shut it down it will climb to the point where it pushes out the overflow tube. Which at this point could be normal as it might be overfull as many times as we added more fluids. The fan will actually pull a rag to the grill at idle, and you can hear it, the old clutch was definitely bad.
Still seems to want to run hotter then I like at this point I am starting to wonder if the radiator has something wrong with it, guess will have to get it to a shop and have it checked.

[sixtyeight]

You stated that it will pull a rag to the radiator. Will it pull the rag along the edges of the radiator also? Sometimes without the fan shroud the fan will only pull air through the area just in front of the fan. The shroud will force air to be pulled throughout the entire surface area of the radiator thus utilizing the complete radiator instead of maybe only two thirds of the surace area.

[kb8n]

Well from the grill by the parking light which is towards the side of the radiator is where I tried that and it pulled it there so I imagine that it is getting some through the sides. Quite a difference from the origional fan clutch though, just want to get it so he can drive it without worrying about overheating at a cruise or show. Plus like I say it just doesnt seem right unless the radiator is somewhat plugged.

[goat2789]

i went through the same thing you are. a new desert cooler radiator and fan shroud and my problems are gone

[mdkrusemark]

Could it be that your running the engine lean? I dont know how much this would affect the temps but it is something. Besides what others have said, make sure the rad. isn't plugged and make sure the bottom rad. hose is in good shape internally. Thats about all I got. Good luck on figuring it out.

[FHummel]

I will ask a stupid question here, but maybe not (?) When you said that you set the timing, I assume you meant with the vacuum advance disconnected and the line to the intake manifold plugged? IF you set the timing with the advance hooked up you will in fact have set the timing very much retarded and could account for your excessive heating. I had to ask because sometimes we do overlook what are ordinarily simple procedures. We've all done it.
I had a 455 engine that ran extremely cool (especially for a 455). With a 4 core radiator, fan shroud and an 18" diameter 6 blade fan with heavy duty clutch, the temperature consistently stayed at 160 degrees (which was the t-stat temp) even in 90 degree weather here in Georgia. That was while cruising. When idling in those conditions the temp would get up in the 190 degree range - still low for a 455. So the big cube engines can run cool with the proper perriferal equipment. This was also with an automatic trans and I did use an auxilliary cooling coil for the trans fluid to supplement the radiator cooling.
Frank Hummel, Jr.

[getmygoat]

My vote is also the radiator.. I had the same problem in October with my new build...

I fused and fused with two cars - impellor clearance, timing, mixture, thermostat, etc..

I'm sure sometimes those things make a difference.. In both my cases, the problem was traditionally obvious... radiators become less efficient over time and just don't provide the cooling capacity necessary for these beasties.

[gtohunter]

My kid has a 2002 Dodge Durango, and it was doing pretty much the same thing. After water pump, thermostat, clutch fan, flush, etc., still overheated. It would slowly creep up and nothing you could do would bring it back down. Changed the radiator, and problem went away. While there was good flow through the rad, once I busted the tank and looked at the tubes, I saw that they had a corrosive coating on them, and I assume no heat transfer for that reason. Even a flush wouldn't touch the corrosion.

[kb8n]

Thanks for all the tips and advice, I have suggested this (new radiator) to the cars owner and I think he is going to order one soon, I will keep you posted when it is installed.