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View Full Version : 400 SBC - Still Running Hot - About Ready to Give up!



TonyD
08-07-2006, 09:56 AM
Guys, I hope you all arent tired of 'overheating topics' but I've been almost everywhere with my 400 and it is still running hot. Without tearing into the engine - I don't have a clue what it could be!

Here's what I have:
400 w/Factory Iron Heads
Hi-Flow Mildon water pump
180 Hi-Flow Mildon Tstat
Modine 951 Radiator
Thermal Clutch 6 Blade Metal Fan
50 Antifreeze 50 Water & Redline water wetter

Here's how it runs:
Test last night - 90* high humidity
Warmed up quickly to 180*.
In stop and go, was a consistent 200-205*
50mph cruising - ran a steady 195*
Stop and go Hard Driving - 220* !!

Conclusion
Under normal light driving, the temps stay down. But under a load, stop and go, they creep up too hot.

What I need to do IMO
- Move the Clutch Fan closer to the radiator (right now its about 5" away.

Other than that, I dont have a clue why the cooling system cannot handle the heavy driving.

Any ideas or suggestions are VERY welcome.
TIA

hardline_42
08-07-2006, 11:28 AM
If your temp readings are off your water temp gauge, where is the sending unit located? If it's in the head, it tends to read higher than normal. Ideal location is usually the intake. Are you running a fan shroud? If this is a street driven vehicle you need to run a shroud with the fan blades at least an inch into the shroud. Lastly, what is the head casting number? Are you sure it's the stock head? If it came off of any other block besides a 400 or is an aftermarket head there's a posibility the steam holes weren't drilled, causing the engine to overheat.

TonyD
08-07-2006, 11:43 AM
has a factory shroud, temp sender is in the intake.

not sure about the heads, if they match the 400 or not? guess that is the next step, is to check on the steam holes...

hardline_42
08-07-2006, 11:52 AM
Just pop off a valve cover, get the head casting number and go to www.mortec.com to decode it. If it's not an original 400 head then you know the steam holes are suspect.

TonyD
08-07-2006, 11:53 AM
thanks hardline, will do that.

baskin
08-07-2006, 05:04 PM
If you take a look at the factory set ups with a fan shroud, you'll find invariably that only the front half of the fan is within the shroud, and that's done for good reason.

The mechanical fans require a high blade pitch in order to move a reasonable amount of air at low rpm, and the higher the blade pitch, the more the air moving through the fan rotates, it's a tangent function with respect to pitch. In other words, a fan with a 45 degree pitch will accelerate the air rotationally to the same degree that it will straight through the blade. The rotation, obviously, moves the air towards the outside of the blade and in order to take advantage of this, at least pat of the outside of the blade needs to be unblocked by the shroud. The difference in performance over having the fan fully shrouded is pretty substantial.

hardline_42
08-08-2006, 05:29 AM
If you take a look at the factory set ups with a fan shroud, you'll find invariably that only the front half of the fan is within the shroud, and that's done for good reason.

The mechanical fans require a high blade pitch in order to move a reasonable amount of air at low rpm, and the higher the blade pitch, the more the air moving through the fan rotates, it's a tangent function with respect to pitch. In other words, a fan with a 45 degree pitch will accelerate the air rotationally to the same degree that it will straight through the blade. The rotation, obviously, moves the air towards the outside of the blade and in order to take advantage of this, at least pat of the outside of the blade needs to be unblocked by the shroud. The difference in performance over having the fan fully shrouded is pretty substantial.
I always wondered why the the factory fans were set up that way. In any case, I'll be running my Mark VIII fan with a DC Controller as soon as it comes in (wink, wink, cough, cough) on my 406.

BADVELLE
08-08-2006, 06:30 AM
What type of radiator are you running? I have a 406 that was in my Chevelle, now in my dad's 71 Nova. I always had it running between 210-220 degrees, did not like that, however, one way that I was able to bring it down some was to run a mechanical fan that I had a buddy that ran circle track order for me, worked better. Now, I also ran a large 2-row aluminum radiator (AFCO), these are generally known in the circle track arena, but worked very well for me. When we put this in my dad's Nova, changed the radiator to an aluminum one, factory fan/shroud, aluminum factory style water pump, car runs continually around 190-200 degrees, maybe creaps up to 205, but on the average is 195. I just thought some of it is to do with the style of car, ie, airflow or hot air being able to escape from under the hood.

TonyD
08-08-2006, 09:20 AM
good point about the factory fan setup. i figure they have it that way for a reason. my fan is now, half in/half out, so i'll leave it.
my 400 turns my under hood into an oven.
im going to double check my timing, and A/F ratio. also am going to a 30/70 mixture.
from there ill test it with an aftermarket guage and if need be, get the numbers on the heads to check them.