I have a overheating problem that in my 67 that has completly got me a whits end. Bought the car three years ago with a matching numbers 396, original harrison radiator without a shroud and a four blade fan. Overheated badly at idle. Found that all the bearings were gone and during the last rebuild the pistons were sized in the bores correctly (to tight). So, had the motor rebuilt, dynoed (423 hp) etc. Still overheats. Now have the following:

Alumitech Radiator
Steward waterpump
Steward 160 thermostat
5 blade fan with clutch
fan shroud

Running 10 degrees advance right now (going to drop it back a tad). Have tried both Rochester (gone through completely) and a holley carb - no change. Pulley's are all 67 numbers correct. Ignition is not electronic (points).
Car runs up to 220 degrees at idle (with 60 degree outside temps) and will keep climbing. This is varified with both gauge and a heat gun. Don't have a overflow tank. Temp will drop back to about 195 once going down the road.

Any ideas?

Is your fan clutch new? Typically slow speed cooling problems means the fan clutch is toast (Assuming a well functioning system).

Since it cools when you are driving it's an airflow problem. Maybe you could get a HD fan clutch, the one with the little springy thing in the front.

David

Hi,
Fan clutch is brand new. Used to run a Four blade (now a Five) without a clutch. I will recheck it.

Thanks

This sounds like a issue another member had a few months back
here is the link to that post read the solution in the last page posts ... there were 75 post of team members trying to help this guy ... it turned out to be a timming issue .
read carfully
http://www.chevelles.com/forums/showthread.php?t=99322&highlight=alumitech+radiator

DON

Thanks for the reply. I pretty sure it is one of two area's, but not in the cooling system itself. With the alumitech radiator, steward pump, shroud, multiple thermostat's etc.. (and new heater core - old one was leaking), I think the cooling system would be good for a lot hotter engine than I have. I don't think it's in the fuel system either. Not running lean at idle as have checked the plugs (not too hot a plug either) and run two different carbs with the holley setup rich at idle. I think it is in:
1) the ignition - my next area to tackle (timing etc) or
2) the block itself (although with the cap off and thermo open - it looks like I'm getting good flow). Everytime I change the fluid I'm getting a lot of "crud" coming out. Block was flushed and hot tanked, but who knows?

I also have a hopped up 454, and that runs consistetly at 180 - maybe an ignition swap for in order (electronic ignition) just to rule things out.

Thanks for the reply's

I have found that an incorrect shroud/fan/clutch will overheat at idle. Once you get going, the air passing through the rad will take car of the cooling by itself.

I dont have the correct shroud on my car, and it slowly creeps-up at stops and quickly drops once I get going.

How exactly would a incorrect shroud and fan combo effct it at idle? Like to small a combo?

Scott72,if your running an aftermarket perf cam of any kind they like to run at apporx 16-18 (+- a couple deg)deg btdc intial advance with vac plugged and idle low as to eliminate mech advance from comming in while adj timing.

Your 10 deg intial is way too retarded for a perf cam which can cause the motor to run hot esp at idle and if you dial it back more as you stated you were going to do it will run even hotter,loose more power,waste fuel,and run like a dog.

You should be running a 180 deg high flow stat because 160 is too cold for optimal power & perf and a 180 deg stat should be fine for any properly installed/working cooling system.

Are you running an elec or mech temp gauge?

The elecs can be inaccurate at times but with that said if your running the temp sender in the head by the ex manifold that in it's self will FALSELY drive up your temps esp when sitting in traffic. The exhaust manifold/headers can heat up the meatal cable for a mech gauge which happened on my 396. I used some of the old tar impregnated wire harness cloth used on the 60's cars to cover the metal mech temp sender cable that would soak up the heat (esp at idle/in traffic)which reduce the sitting in traffic idle temp on my car by 6-8 deg. I insulated the temp sender cable from the head all the way to where it entered the firewall to eliminate all possible areas for the cable to get heat soaked. I cut a slit down the insulation to slip it over the temp sender line then i used small blk tie wraps to close it back up which looks neat and not sloppy when done,it's hardly noticeable.

Also,i got 2 temp gauges that are used for AC work and i stuck them in the rad opening with the motor heated up on a warm day idling in the driveway.
When the new autometer mech temp gauge read 220 in the car idling the coolent temp in the rad was 190-195 ish on both thermometers. I had also tested the new autometer mech temp gauge by placing it in water on a stove and boiling it and it was right on the money to esure it was calibraqted correctly.

Story here was the mech gauge temp sender reads approx 20 deg higher when installed in the head by the ex port which can over drive the heat temp which makes sence. Thats not to say the there are not any hotter spots in the motor while running which there are but overall a temp sender in a head by the exhaust reads higher than actual avg overall coolent temp in the motor/coolingsystem . But i am sure that the coolent that is in the heads by the exhaust is running somewhat hotter than the rest of the motor which does over drive temp sensors causing people to chase thier tails at times trying to fix a heating problem they dont really have. Temp senders placed in after market intakes always read much less than temp senders in a head by the exhaust.

You never mentioned if your car ever spits up coolent when in traffic showing your actually overheating so if it doesn't do that if your running a good 15lb cap (new/known good 15lb cap is important) that's a good sign because if it were overheating it would spit up at times in traffic. But make sure the coolent level when the motor is cold is approx 2-3 inches below top of rad . This is to allow for expansion of the coolent,if the coolent lvl is too high it will spit up when hot looking like it's overheating when it's just spitting out the expanded coolent because it has no place to go so check your coolent lvl when cold to ensure it's 2-3inches below the filler neck.

The bottom line here is bump up our initial timing to 16-18 deg btdc & insualte your temp sender line if its a mech gauge which should reduce your idling temp some.If may reduce it by approx 5-10 deg total due to advancing the initial timing & insulating your mech temp sender line.Then get an AC thermometer that goes to approx 200 deg so you can test the delta between what your mech gauge says at idle vs what the actual coolent temp is in the rad while idling hot which will at the least show the gauge is reaing a min of 10-15 hotter that what the coolent in the rad is running and i bet you will be good to go after that.

Latsly,if you do all this and things improve but are not great then try using a H/D fan clutch as most std ones have a higher cut in temp and the H/D one's will have a lower temp cut in temp. But the h/d unit will cool better at the cost/trade off of pulling more dust/dirt into engine compart,more fan noise,use more fule in traffic/slow speeds.

Are your fan blades apporx 1/2-3/4 of the way into the fan shroud,if not adj usung longer bolts/studs/ with washers to attain that.

Watch/listen for detonation if you decide to crank up the initial timng where it belongs. If it detonated bak the intial timing off a deg or 2 but dont go lower than approx 15 deg btdc intial but avoid going this low if at all possible.

Let us know how you make out.

Scott

Brovo ... Brovo
This Is The Kind Of Input We Love To See !!!!!!!!!

Yep, Excellent information and advice.

My$0.02

i would def. replace the 160 ther. with 180(of course, this could make it worse, holding the water in the block longer)-the way its running now, the 160 is just wide open all the time-i would think you need more fan blades than 5 for idle temps to come down-try and experiment with diff blades
im surprised the temp doesnt come down more driving along, sometimes the water runs thru the rad. to fast and doesnt have a chance to cool, i have tried restrictors with some suc.-theres always the chance there was some core shift when the motor was built, or crap got in there over the years, blocking flow-i remember back in the 60's, i bought a new 396 nova, it would overheat all the time, and it was all factory-we tried everthing, could never cure it-you have to try stuff, hopefully you will hit on something, i would shoot for lowering idle temps first-try sticking a window fan in front of the car, see if it helps, might give you an idea of air movement

There are some fantastic posts here with alot of good information. As previously stated...the timing issue is huge and not only should you have at least 14ish BTDC timing set in for a static setting, vacuum advance will help optimise your situation and help with some of the "overheating" issues also. Run full manifold vacuum if so equipped! It's a good thing.

While we will take for granted your readings are accurate, where is your sensor? Heads or intake. The intake position is the most accurate and head locations can become tainted with exhaust manifold/header radiation! So, keep that in mind. And it appears that you are keeping your coolant in which is good!

Notwithstanding all that.... most applications that will cool when cruising down the road and not at idle are in fact airflow issues at idle. The use of aftermarket "clutched" fans are generally okay, but these fans are not what they used to be and my major issue with these is that they are a "universal" design which in turn are designed to replace literally dozens of specially designed and functioned fans of yesteryear. Also, you NEVER KNOW if your clutched fan system is working at 100% of it's capacity??? A clutched fan only turning at 85% of it's full potential can have dramatic effects on airflow production...and you just can't tell that's going on. And...the shroud system IS important too. The fan should have no more than 1" of spacing at the far reaches of the blades to the shroud and should be placed at 1/2 to 3/4 into the shroud opening. This usually is the optimum situation.

I have converted several Chevelles and Camaros from clutched systems to heavy duty flex series fans from Derale with great results! I run one on my 400+ hp Camaro with air and sitting in 100 degree traffic and stays right on the thermostat cycling point. The Derale 17XXX series are excellent airmovers and relatively quiet as well. If you get one from Summit at approx $65... you can see if the airflow was at least the issue. Running it is up to you. You WILL need spacers to position the fan correctly.

Good luck and tell us what happens.

ps...the 160 thermostat is indeed too cold for your application and will have NO effect on your cooling ability.

OPPS,i forgot to mention in my above post i am running a 396 with stock gm 7 blade clutch fan,std clutch unit not the H/D one,milodon high flow pump,180 deg high flow stat,stock shroud,25 yr old harrison 4 core radiator.
My motor is basically stock with the exception of a mild hyd perf cam and it's running apporx 9:8-10:0 comp with a 4spd & 3:31 gear.

On an 85-90 deg day my 396 runs at apporx 195-200 deg while at cruise but keep in mind my mech gauge sending unit is located in the head next to the exhaust port and it reads approx 6-10 deg higher due to close proxmity to exhaust heat as explained above in my prior post. So I am really running at apporx 190-196 deg with all stock gm equipment. It runs at 185 deg while cruising on 80 deg or less days.

While in stop/go slow moving traffic in 85-90 deg heat it will heat up to approx 210 in 5 mins and 220 in 9 -10 mins but remember i have to reduce that by a min of 10 deg because of the delta between the mech gauge temp & actuall coolent temp at the radiator as explained in my above post.

So it's really running at 200-210 deg on a hot day sitting in slow stop/go traffic with a basically stock cooling system which is not that bad for a BBC. Yes it's right on the edge heat wise but it's acceptable considering it's a BBC without a more efficient Alumitech Rad which i would like to have but cant afford right now and i want to keep the stock equip if poss too as i show the car at times. But it does cool down a couple mins after getting back up to cruise speed after sitting in traffic.

Scott

Thanks for all the excellent information. Ordered a 180 thermostat, so that's done. Also advanced the timing which did help a tad. Brought it down to a buddy of mine that used to build motors for Calloway. He thinks I'm just not pulling enough air through. I tend to agree with that. On the highway with the 160 still in it (and 40F outside), temp would drop right down to 160-165F. Would still creep up at idle over 210. Ordered a different pulley to spin the pump/fan a little faster. May try a Flex fan or go with and electric pusher fan in the front. Have all winter to decide on a plan of attack. Car is (well was) very stock looking which a like. But I guess performance comes with a price in terms of originality (car came with no shroud, four blade fan, and three core Harrison.

Anyway - thank you for all the info.

Dont think I saw one of the most obviose things checked! the radiator cap. Seems like a simple divise right!! But if working correctly it will increase the boiling temp. of your coolant by as much as 3 degrees for ever pound of pressure. Really!! You need an overflow tank and working cap. or jus treplace it with a good 15lb-er. increasing your boil;ing temp by 45 degrees.

forget the 5 blade fan, go with the stock 7 blade clutch fan max diameter to fit inside the shroud. also, make sure the fan blades are not turned around. the front markings are facing toward the radiator. I have seen some where the pitch is wrong.

Hmmm, check what an AC or HD cooling system had that year. Probably a HD radiator, shroud, 7 blade fan and HD fan clutch. If you're interested in checking your fan clutch, this might interest you

http://www.autoacforum.com/messageview.cfm?catid=20&threadid=10772

My $0.02