I'm running an 18" 6 blade fan and thermal clutch on my 67 SS 396/325 with an Alumitech Radiator. No problem with heat even with the AC on while running at freeway speeds. However, it will start to heat up when stopped or in slow moving traffic. I assume it's an airflow issue. When I installed the aluminum radiator, put the fab shroud back on, I noticed the the fan sits deeper inside the shroud than it did with the four core Harrison. If I trimmed the fan shroud allowing more of the fan to be exposed, would this improve the rate of airflow? I've always thought the fan should be half in and half out of the shroud. Thanks in advance for your input.

Be sure your fan clutch is OK...

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

My $0.02

Thanks JJ for your response, yes, my fan clutch is new, so it should be ok.

Anyone else have an opinion regarding the air flow question?

Anyone?

Have a '67, 396, thirty-over, dyno'd at 463 hp @ 6000, heats up in traffic. Bought it with twin electric fans and Harrison orig brass rad. Changing (next week) to 4 core alum rad and clutch fan. Got a 7-blade, 18-inch OEM fan and shroud with 19" opening. Fan will be about half-in, half-out of the shroud. I'll let you know the results.

Phil,

I appreciate your response. I hope the new rad and fan set-up cure your heating probs. When I installed my aluminum rad, it sits back a little closer to the engine which makes the fan sit deeper inside the fan shroud. Since I have always been told that the "correct" position of the fan was "half in half out", I thought perhaps by trimming the shroud to acheive this, that it would improve the airflow.

Let me know how you come out.

NO..NO>>NO! The perfect "footprint" for the shroud/fan USUALLY 2/3 of the fan inside the shroud (DEPENDING ON FAN BLADE DESIGN), but half/half works okay. If you cut more away...it's likely that you will degrade the performance unless the whole fan is inside the shroud.

I have upgraded a few Chevelles with air for the same reason you have a problem at slow speeds and idle. The problem with the clutches that are available today... even new...are more universal specifications and you NEVER KNOW if they are working at the correct speeds etc. How hot will it get? And does it stabilize there?

I have installed several 18" Derale heavy duty flex fans (series #17XXX) that move more air than your stock set-up. All of these installations worked well to cool even in the most agressive temps.

Otherwise.... a booster electric fan could help if you can sneak one in.

Steve,

Thanks for your response. My fan sits almost all the way in the shroud, maybe a half inch outside of it. Before I installed the aluminum radiator, the fan was very close to 2/3 in 1/3 out, as I recall. This is the reason that I thought of trimming back the shroud a little in order to acheive the half in half out. I'll take a look again to see if I can get it to 2/3 in and 1/3 out. Thanks again.

Steve,

By the way, I don't know what the temp is, as I have factory gauges that don't have numbers. But, as I get in stop and go traffic, the temp rises and I can't honestly tell you that it stablizes.

Phil,

I appreciate your response. I hope the new rad and fan set-up cure your heating probs. When I installed my aluminum rad, it sits back a little closer to the engine which makes the fan sit deeper inside the fan shroud. Since I have always been told that the "correct" position of the fan was "half in half out", I thought perhaps by trimming the shroud to acheive this, that it would improve the airflow.

Let me know how you come out.The new combo works really well. Did a 20-min test drive in stop-n-go traffic. Air temp, 50, and the temp gauge never got above 150. The previous set up (Harrison brass rad and twin elect fans) would have hit 230 under same conditions. It may be working too well now. We have some 80 degree days coming up next week, so I'll test it again. I'll take some pics and try to post them for you.

Phil,

Glad to hear that your set-up is working well. I still haven't "adjusted" my fan shroud yet, been busy with work. The one response I had said the fan should be 2/3 in 1/3 out. I'm not sure I can make that "adjustment" on my shroud, but, we'll see.

Phil,great to see your new cooling system works well.

150deg is too cool for best perf/power/efficiency,you should install a quality 180 deg high flow stat.

scott

I agree
when folks drop one of our rads in I almost insist that they use at lease a 180 stat ... they tend to work well enough to modulate a 160 stat ...and thats too cool ... 180 will burn off moisture in the pan
Don

Phil,great to see your new cooling system works well.

150deg is too cool for best perf/power/efficiency,you should install a quality 180 deg high flow stat.

scottYou were correct. I had a 160 in it...don't know how...replaced it with a 180 and now it holds 175 in all traffic conditions. The 7-blade, OEM clutch fan is about half into the shroud, and draws a lot of air. I now have an original Harrison brass rad..in excellent shape...and no use for it.

I agree
when folks drop one of our rads in I almost insist that they use at lease a 180 stat ... they tend to work well enough to modulate a 160 stat ...and thats too cool ... 180 will burn off moisture in the pan
DonThanks. I agree.

Phil,

The 7 blade fan and clutch you got...can you tell me where you got them...are they GM?

Phil,

The 7 blade fan and clutch you got...can you tell me where you got them...are they GM?Fan clutch is from Year One, #3491N, $207. The 7 blade, 18" fan is from GMpartsdirect.com. #393996, $63.11 plus shipping $13.88.

Does anbody have the GM part # for the 5 bladed smallblock fan??

where did you get your fan shroud from? Thanks

where did you get your fan shroud from? Thanks
Shroud was from Year One, #DL551, $102.00.

Like most of you I had heating problems with my 67 BB. I had put a new 4 row radiator in last year along with a fan shroud from opg with my stock 4 blade fan, No help. Last week I put a 18" 6 blade flex-a -lite fan #1318 in without a clutch and is 1/2 in and out of shroud. Problem solved. It now runs between 170 and 190 in southern california weather.

I have a 14 inch fan/shroud now in my 66... Will an 18 inch combo fit?

The flex-a-lite 18" fan is accually 18 1/4". Measure the opening in your shroud and make sure it's around 19" or better and the shroud is centered with the fan. If not go to a 17" #1317. Good luck.