put one e fans runs hotter

[rich weyand]

OK, trying to refresh my aerodynamics, BUT....

I think that if the air velocity through your cooling fan at its controlled rpm is lower than the velocity of ram air through the radiator at speed, you will get more air flow at speed with the fan off than with it running. The fan is effectively slowing your ram air down to its CFM rating rather than letting it flow through at the full CFM that would pass through as ram air with the fan not there. The fan's rated CFM at idle and low speed is more than enough to cool the engine, but not enough when the engine is working to move the truck at higher speed. At that speed, the ram air would be enough to cool the engine, but the spinning fan is now in its way more than its helping.

You can test this by switching the fan off at speed and watching what the temp does. If you are at speed and at temp, shut the fan off. If the temp drops, you need a fan controller.

 

[rich weyand]

I just did a little calculation on my fan for example. It's 16" diameter and 2500 cfm, which is a pretty good number for a fan. That calculates out to the fan moving air through at 20 mph. So above 20 mph or so, the ram air is a higher velocity than the fan can move. At highway speed, the spinning fan might as well be a piece of cardboard over the radiator. It will slow air flow down, not speed it up. That's counterintuitive, but I think it's right.

A mechanical fan on the front of the engine doesn't have this problem because it has very high pitch blades compared to an electric fan and it's rpm (and flow rate) varies with engine rpm.

Anyway, do the test of shutting it off once temp has stabilized at speed and see if temp goes up or down. I think it's going to go down.

 

[NOPHO84K30]

I think that makes sence. I put a cheapo controller I got for free so there ya go. I may just have to go buy the painless f5 even it shuts off at speed. The one im using is 40 amp and one relay for two fans so its probly not at full speed anyway. Tryin to go cheap never works right.....

 

[NOPHO84K30]

Also it is az and its 115' out side. Anyway ill try shutting it off and see if it drops..thanks for all youre help

 

[highdesertrange]

let us know how it works out. inquiring minds need to know. highdesertranger

 

[NOPHO84K30]

Will do im going camping this weekend itll be monday before I can try it..

 

[rich weyand]

Also:

Did you make any other changes at the same time?

What is your base ignition timing set at?

 

[NOPHO84K30]

No other changes made..timings 11btdc it runs like crap any lower.im sure the chain is old and sloppy. I moved the ign wire to a switch and can turn it off while driving now. Will see monday how it runs down the freeway with it off. Hopefully it runs cool with it off. We will see.......

 

[rich weyand]

If you are running the stock HEI distributor, you can go higher with the advance. Chevy V8s, both SBC and BBC, like 36* of total timing, so with 20* of centrifugal in the stock HEI, you could go to 16* BTDC. More advance will run cooler. Just keep an ear out for knocking, though that shouldn't be an issue until somewhere between 18* and 22* BTDC base timing.

I'm really interested in the shut-off-the-fan-at-cruise testing. One part of me says that will help with ram air flow, and another part says not. I can rationalize it either way. Sometimes you just have to try things to know for sure.

 

[NOPHO84K30]

Ok turned it off while driving 65 down freeway. I started at 230* or so climbed slowly turned back on back to 230 so didnt work for my truck.

 

[NOPHO84K30]

Going to clean condenser out maybe its clogged up ? . Mudd bugs crappola and see

 

[NOPHO84K30]

I may try using two 40amp relays ran off the controller for on and off to run fans for full speed. Controller to relays relays to fans.? Just to get them full power each instead of splitting the one relay it has....we will see if it makes a difference...

Ill let ya kno
Its hot running the heater full bore when its 110* outside I laser temped my vents 163* inside cab

 

[350runner]

I'd be looking into a better radiator if I was you bud... good luck

 

[rich weyand]

Ok turned it off while driving 65 down freeway. I started at 230* or so climbed slowly turned back on back to 230 so didnt work for my truck.

OK, well that's interesting. Good to have that resolved one way or the other.

There has to be something wrong with that radiator. Full of garp inside, or full of garp in the fins, blocking the air, or something.

Can you post a pic of your fan setup?

 

[89Suburban]

The shop next to my wrk thinks the lower 1/4 of the rad might be pluged they said to put a new one in and see..I dont want to spend 400 to SEE if it fixes it.

I got my new radiator shipped to my home for a little over $100 from AZ. Best money I spent on this truck. Temp gauge hasn't seen anything over 200 degrees since.