I have a 70 402 in my 67. Rebuilt with a mild roller Hyd cam. Dynoed at about 410hp. Alumitech 4 row radiator, shroud, and a new HD fan clutch with a 7 blade fan.

Temps are usually great - around 170-180 - but I noticed yesterday (95 degree day) when idling for a while the temp climbed to 200. I used my temp gun to watch it climb.

At idle that there is almost no air flow (put my hand carefully beind the fan) from the fan to the motor (idle is at 850). When I kicked up the rpm just a bit, the air flow is a lot stronger. I am thinking that at idle it is not getting enough air - clutch not engaged at that rpm? Should I just rev it a little when stuck in traffic?

Thanks, Mike

I would think that 200 is not a big deal at idle and it should come right down when you start to move. Remember that the Tstat opens at 180. It may not always BE at 180, especially when the air isn't moving. If your higest temp is 200 and only at idle, I don't know if I would be concerned.

Chuck

Thanks - kind of was thinking that 200 is OK....it was still climbing - maybe next time I will see how high it actually goes - reasonably of course.

Does seem odd that there is virtually no air flow when idling though. I always thought the fan speed would move at least some air towards the motor at idle.....

This motor has been through 2 rebuilds in the last year (another story) so I am being very very carefull this time.....

Mike a lot of people would die to keep it where you are this time of year. Not sure where in Ill. you live but a lot of that state is like Texas with high humidity. That means the air is thick,hot and full of moisture and hard to push this time of year. Whose HD clutch do you use? Mine is a Hayden and I can feel a lot of air at 900 with the same fan.

Yeah - I bought the Alumitech and it has helped a lot. Always at 180 or so. Read all the threads last year on the site and tried to make sure I pampered the rebuild investment......I'm around Chicago and you are right about the humidity.

Clutch is from Carquest - Heavy Duty one. I found the 7 blade fan from a 'guy' and to make it all fit I went through 3 or so clutches and returned them. Ended up being for a 69 BB. Short pump. Has to do with the spacing on the clutch to the pump pulley and fan all matching up.

Originally had a 5 blade fan with decent clutch - not new.

Thing is, this is an A/C car. I did add the condenser in the spring. All is hooked up but system not charged yet. I wonder how much more heat running that compressor will create?

Is the Hayden clutch much better? Their web site seems to say so....

Mike Scott has done some research on these clutches and found the NAPA and Hayden truly do lock up longer and some that are advertised as HD are not much more than standard. My reference was a big block police car with A/C. Run a search for Hayden and you will get a part #.

My 69 has a brand new 396 with A/C that is not charged like yours and will run 30 minutes in my shop @ 2000 rpms and struggle to get to 180*. It does have a stewart water pump and that may be the difference. Also have an Alumitech radiator.

Mike Scott has done some research on these clutches and found the NAPA and Hayden truly do lock up longer and some that are advertised as HD are not much more than standard.


I believe the better NAPA clutches are made by Hayden. I've found them to be the only aftermarket clutches even worth putting on a car. (NAPA in my area also carries a "cost effective" line to compete with the chains). I've found that a worn but working OEM fan clutch often performs better than many new "inexpensive" ones, even clutches said to be HD.

My experience here comes from an AC performance perspective though.

I guess the moral of this story is......... Take nothing for granted.

Thanks for the input. I think I might get a Hayden clutch. Seems a minimal investment - at least compared to the Alumitech (best thing I did by the way).

Haydens site catalog is defined by measurements so I have to be precise. I'll also research the Napa - Hayden relationship. Then I can cross reference ny current one.

Thanks again.....

here ya go .. seems everybody like's them in combo with the Aluminum rad .

http://www.haydenauto.com/products/fan-clutches-and-fan-blades.htm

Heavy-Duty Thermal
Turns the fan 80-90% of the shaft speed when engaged for increased cooling.
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 26.0 Sq. In. of working area allows higher operating RPM’s.
Identified by finned aluminum faceplate and thermal spring on the front.

Are you running a shroud and just as important is the fan clutch reall h/d?

Ground and other are selling what they call h/d fan cluthces that are clearly not h/d units.

When the motor is at approx 200 deg or more a h/d ac type fan clutch should be looking up giving decent fan rpm to engine rpm ratio at that point.

And yes,very good idea to idle motor a little higher in the hot summer months so fan rpms more when in traffic for more airflow thru rad just as long as the fan clutch is hd enough/locking up enough/working correctly to do the job which some fan clutches mfg today dont do,period.

I have found some fan clutches mfg these days dont work very well esp the std duty clutches that are being marketed as HD that dont have very good lockup which can easily cause the motor to run hotter at idle because they dont spin the fan enough to efficiently cool a bbc in traffic on a hot day.

Napa & hayden have the best fan clutches i have found in past few yrs.

If your running the 772 type gm 7 blade clutch fan get one of the clutches listed below because it sure seems like your fan clutch isnt locking up enough which will cause your pronblem in traffic and i know 1st that these clutches work very well that i litsed below.

NAPA 271303 - H/D CLUTCH

HAYDEN 2747 - H/D CLUTCH

Also make sure you base timing is enough when running a perf cam too along with running a vac adv for street because retarded base timing with perf cam (need approx 18 deg) and no vac adv(hooked to full vac all the time) at idle can both collectively or by themselves make a motor run hotter at idle too.

But you did mention 200 deg when sitting in traffic which is not that hot for a bbc but did it go any higher and is yes how long were you in traffic and at what outside temp.

Scott.

Hayden (and it's subsidiary Imperial) state that their HD and SD clutches lock up a lower temp (170 deg air temp, or 180-190 deg water temp) than others. OEM lockup temp for trucks was 210 deg. So other clutch manufacturers might be using the OEM specification.

I saw 2747 Hayden one on the web site that matched.

You know, the Carquest HD clutch I have has to move that 7 blade fan at idle. If it is even a little weaker than the others it probably has trouble doing that. I'm sure you are all correct that the lower temp lockup with a Hayden will solve that.......