k10 big block cooling problems

[dieselfuel007]

i have a k10 with a mild built 454 thats having some cooling problems at idle the gauge runs straight up going down the road but if i let it idle it starts to run over on the hot side of the guage i've used a temp gun on the thermostat housing its around 200f when the gauge shows it hot but when shoot around the sending units its 210-215f . this is what i've done so far 7 blade fan gm heavy duty fan clutch repop big block fan shroud new 16 ibs stant rad cap added recovery tank timing is good carb runs alittle rich also it has a wieand aluminum short water pump short and the fan is half in the shroud it has a 4 core radiator that was in the truck when i bought it i really don't want electric fans either

[jimijam00]

nothing wrong with those temps on a big block

[Steeveedee]

200 is about where mine runs, now, idling in hot traffic. I ended up putting in a high flow thermostat, and that licked the problem.

[dieselfuel007]

its just not a good feeling to look down a the temp guage is 3/4 to hot i'd try the high flow thermostat is that something special and what temp thermostat did you go with

[sauxs]

On chevelles.com website there are multiple articles about cooling a BBC. I was having cooling issues with a 454 in a 67 Camaro. I made some changes outlined in the articles and now I don't have any issues.
The article recommends to use Hayden 2747 fan clutch with a part #3947772 ("772") GM fan. The article claims a 160 degree thermostat from auto zone outflows most and is the one to go with.
The only thing I did different from the articles on chevelles.com is a different fan. The fan I went with was a reproduction part #3976064 ("064") 70 LS6 fan. This fan will pull more air at low speed than the "772" fan. Now I don't have any low speed overheating.

Hope this helps,
Steve

[jimijam00]

Originally Posted by sauxs

The fan I went with was a reproduction part #3976064 ("064") 70 LS6 fan. This fan will pull more air at low speed than the "772" fan.

Source? I didn't see that in any of SWheaton's posts.

[dieselfuel007]

i just ordered the fan you suggested it does seem to be an airflow issue and i'll try swap the thermostat its been a while since i've drove with out electric fans but i never seem to hear the fan locked in shouldn't it be louder when the engine heats up i even let it set at 1800 rpm for a few minute in the driveway and it made no difference

[Steeveedee]

I'm running a 180º thermostat. Nothing real special, I got mine at NAPA. Just drilling 3 #10 holes in the old thermostat was enough to bring the temp down, but it took longer to warm up.

[72c20customcamper]

Originally Posted by sauxs

On chevelles.com website there are multiple articles about cooling a BBC. I was having cooling issues with a 454 in a 67 Camaro. I made some changes outlined in the articles and now I don't have any issues.
The article recommends to use Hayden 2747 fan clutch with a part #3947772 ("772") GM fan. The article claims a 160 degree thermostat from auto zone outflows most and is the one to go with.
The only thing I did different from the articles on chevelles.com is a different fan. The fan I went with was a reproduction part #3976064 ("064") 70 LS6 fan. This fan will pull more air at low speed than the "772" fan. Now I don't have any low speed overheating.

Hope this helps,
Steve

I haven't been on the site for a while my screen name is Markss66

Originally Posted by jimijam00

Source? I didn't see that in any of SWheaton's posts.

I talked with him when I was redoing my Chevelle he lived a few miles from me . Wealth of cooling knowledge

[72c20customcamper]

Originally Posted by dieselfuel007

i have a k10 with a mild built 454 thats having some cooling problems at idle the gauge runs straight up going down the road but if i let it idle it starts to run over on the hot side of the guage i've used a temp gun on the thermostat housing its around 200f when the gauge shows it hot but when shoot around the sending units its 210-215f . this is what i've done so far 7 blade fan gm heavy duty fan clutch repop big block fan shroud new 16 ibs stant rad cap added recovery tank timing is good carb runs alittle rich also it has a wieand aluminum short water pump short and the fan is half in the shroud it has a 4 core radiator that was in the truck when i bought it i really don't want electric fans either

The electric senders are notorious for being inaccurate. If you look at the factory gauge it's got a huge "normal" range my 72 350 the gauge stays just above the first tic . But my mechanical will be at 185-190. If your running at 200° water temps at idle its withing range . My 496 use to run those temps all the time with mechanical clutch fan . I switched to a DeWitt 2 row aluminum and spal fans . The fans come on at 195° water temp in the rad . The mechanical temp in the head is 215° to 220° when the fans kick in head temp will always be higher than the water in the rad . Your right above the cylinder where the most heat will be in a rather small water chamber .

[sauxs]

I purchased a reproduction fan #3976064 from drclassic.com

[dieselfuel007]

thats where i ordered mine from to i'm gonna try that and a thermostat swap really don't want to change my fan clutch just yet its a gm heavy duty i bought nos and it was really expensive

[Stocker]

Originally Posted by dieselfuel007

really don't want to change my fan clutch just yet its a gm heavy duty i bought nos and it was really expensive

That fan clutch should be more than up to the task. You might also consider sealing the shroud to the radiator; there's a recent thread here somewhere....

If you really feel the need to upgrade to a severe duty fan clutch, Hayden lists a few comparisons. https://www.haydenauto.com/en/produc...-types/thermal

Heavy Duty
Turns the fan 70-90% of the shaft speed when engaged for increased cooling
Turns the fan 25-35% of the shaft speed when disengaged
Used with deeper pitch fans (2-1/2” of pitch)
Land and groove design with up to 27 sq. in. of working surface
Identified by finned aluminum faceplate and thermal spring on the front

Severe Duty
Turns the fan 80-90% of the shaft speed when engaged
Turns the fan 20-30% of the shaft speed when disengaged
Used with deeper pitch fans (2-1/2” of pitch)
Land and groove design with up to 72 sq. in. of working area
Larger working surface provides cooler running and longer life expectancy
Thicker body and deep finned faceplate dissipates more heat
Can be used in place of many heavy-duty clutches

[sauxs]

From chevelles.com website:

#12 · Jan 12, 2017
Robinls5 said:
Not sure about your year car. The 3947772 Fan blade was designed for the 70-72, 69 ? for the 3:31 Rear end. The 70 LS-6s also used the 772 fan blade with 3:31 Rear. NOW if you ordered the factory 4:10 rear gear, The 3947772 fan blade was replaced with a different number fan blade , I forget that number. Same size, BUT a different pitch on the blade.
Its all about moving XXXXX number of Cu. Ft. of air per. Min. through the Heat Exchanger or Rad.
Bob


3976064 LS6 with 4:10. Dates M69 and E70. >

[jimijam00]

The BBC off the dealer lot needs the same idle and low speed cooling as the next, regardless of diff gear, so the change likely has nothing to do with more cfms at low speeds. Maybe it had something to do with to do with HP savings on those cars with 4:10s because they reved higher and quicker.

[Steeveedee]

I agree with your cooling assessment, but shouldn't the clutch "free-wheeling" take care of the HP savings? My non-AC '64 Impala with SHP 30 HP 327 was equipped with a fan clutch (no A/C). Though in fairness I should point out that the original purchaser worked at the assembly plant where it was built, and followed it down the assembly line. He probably conned a clutch fan out of the assembly guys. Not an SS, but it got SS wheel covers. He bought it to street race, and did a lot of it.

[Caddylackn]

An improper idle mixture can cause overheating at idle. I would fatten up the idle mixture some and see if it improves.

Improper timing can also cause overheating. What is the base timing set at?

[dieselfuel007]

i went out and looked and it has a 772 fan on it now hope the new one helps its run 16 degrees of ignition timing at idle when the vacuum advance is unhooked one thing i'm gonna look at is to see if the vacuum advance is on ported vacuum and change the fan and thermostat and see if that helps also put a mechanical temp gauge on it we'll see what happens

[dieselfuel007]

just swapped the fan and checked i had the advance hooked into ported vacuum hooked it to manifold vacuum on the carb just above the intake manifold and it seems to run cooler down the road and idle but i just took a short trip i really think it was where i had the advance vacuum going to manifold vacuum that made the difference i'll get it out this weekend and see if its cured thanks to everyone for the help

[Caddylackn]

I recommend checking the advance curve on the distributor. Get yourself one of the new timing guns with digital readout that measures advance and rpms. They are pretty cheap now. Then run through some rpms and record what the total timing is. Do it with the vacuum advance and without it. You can change your spring weights to tailor your advance curve where you want it. Get one of those timing advance curve kits, that has the adjustable vacuum can and the max. vacuum advance adjustable lockout plate. they are about $35. Their instructions are pretty good on how to install these.

The stock vacuum advance can can give you way too much advance and should be limited to only 10 -16 degrees or so (5-8 degrees at the distributor). I would want all the mechanical advance in by 3,000 rpms or so and the total advance for a BBC with iron heads is somewhere around 32-34 degrees (no vacuum advance). So if you are running 16 degrees initial timing, your mechanical advance should only pull around 16-18 degrees more timing. That gives you the 32-34 total advance. Then the vacuum pulls in another 10 - 16 degrees at part throttle only. With the advance spring kit, you play with changing the spring weights until you get 32-24 total advance with vacuum plugged at around 3,000 rpms. Make sure you are getting no mechanical advance at idle. This can cause an erratic idle and other issues.

Then plug in the vacuum advance and play with the advance lock out plate until you only add a max. of 10- 16 degrees with vacuum as checked with the digital timing gun at part throttle. The can is also adjustable and adds a restriction via an orifice on the vacuum line, so it slows down adding in vacuum advance, which can prevent pinging at part throttle acceleration.

The stock advance curve set up sucks and was designed for emissions alone. A custom recurve will give you the best gas mileage and performance.

If you get an aftermarket performance distributor it usually has these parts installed and make it easy to limit total vacuum advance, and change the mechanical advance curve.