Fan Clutch Engages @ 70+mph

[DA BIG ONE]

I'm concerned about fan clutch engaging at a steady 70 mph, or above. Looks like a -30 deg swing on temp gauge, then stays off for awhile, then back on again. Fan does not engage under under 70 mph.

Only thing I'v done lately relating to cooling system is change out the dual thermostats w/190 deg units, topped off and bled system.

What should I be looking for, or?

[JoeyD]

I think your winch bumper is blocking some air flow through the radiator causing the temp to come up enough to engage the fan. The faster you go the more the wind will be blocked due to air flow.

[DA BIG ONE]

Originally posted by Joey D:
I think your winch bumper is blocking some air flow through the radiator causing the temp to come up enough to engage the fan. The faster you go the more the wind will be blocked due to air flow. Interesting, I did not think of this.

Just reviewed instructions for bumper and it clearly states 6.5 td requires the optional air intake scoop across bottom edge of bumper, I have it.
Considering the bumper edge design (flat) along w/their scoop design I can see where air would flow past scoop at speed. I now see where the oem 6.5 td bumper design/function come into play.

I now will tinker to see if I can improve airflow to/through radiator by making my own cutouts in both outside edges of bumper under lights. Then use some composit air intakes and 4" hose direct into rad. I was thinking of dropping the WARN air scoop by a few inches, but it would restrict flow over IC this way.

I can see how the obvious is overlooked, thanks!

[JoeyD]

It could be the winch itself depending on how high it sits in the craddle in the bumper.

[john8662]

Which fan clutch do you have Factory, KD, Hayden?

Have you modified your factory clutch if equipped?

[DA BIG ONE]

Originally posted by john8662:
Which fan clutch do you have Factory, KD, Hayden?

Have you modified your factory clutch if equipped? Factory, and not modified. How do I mod the factory unit?

[HowieE]

There are 2 things that arte happening at 70+ that can effect this. First the engine in general is producing more heat, not the main cause but an effect none the less. Second the air flow through the system changes configuration with speed. It is common for us northerners to have this problem while running with our snow plows raised. I would show a notisable rise in temperature above 35 mph if te plow was raised. Whith that in mind look for anything you may have installed that could be changing the air flow into or over the engine and out below.
Just from the age of your truck I would also suggest looking at the condition of the spaces between your coolers, AC condenser, and radiator. If you want some idea of what to look for see my web page. http://mysite.verizon.net/vze54tx9/

[DA BIG ONE]

Upon careful examination I find that I can cut out 2 large square openings to each side of the winch (larger than oem bumper openings), but I need to weld in some reinforcement at a right angle and around openings to ensure structural integrity.

Before changing out the thermostats fan clutch never came on at highway speed, but I had a way too cool running motor w/heat transfer issues, along w/crappy milage too.

The other thing I had done was install the B&M supercooler which is about 1/3 larger in size than factory setup.

[DA BIG ONE]

Originally posted by HowieE:
There are 2 things that arte happening at 70+ that can effect this. First the engine in general is producing more heat, not the main cause but an effect none the less. Second the air flow through the system changes configuration with speed. It is common for us northerners to have this problem while running with our snow plows raised. I would show a notisable rise in temperature above 35 mph if te plow was raised. Whith that in mind look for anything you may have installed that could be changing the air flow into or over the engine and out below.
Just from the age of your truck I would also suggest looking at the condition of the spaces between your coolers, AC condenser, and radiator. If you want some idea of what to look for see my web page. http://mysite.verizon.net/vze54tx9/ After viewing your photos I'd better have a looks see between all my cooling options too!
Thanks

[JoeyD]

The fan uses the air coming through the grill to determine when to engauge. The added coolers could be throwing off just enough additional heat combined with the winch to do it.

[G. Gearloose]

I concur howie,
I summize with a plow raised and above 40 mph on my K5, the airflow reverses and air is drawn backwards through the radiator into the low pressue area behind the plow, but not enough volume to really cool the radiator. The fan clutch never sees radiator air, only cool air from below, so it boils over on the hiway when its 10 degress out. Happens quite repeatably.

[DA BIG ONE]

I have some more options for a fix to the flat bumper face forcing air over hood and under suspension at speed;

Use pipe say 6" dia, drill hole in face of bumper and insert/weld 1" section of 6" pipe,

Fabricate 2 flat wings to fit above & below front flat section of bumper spaced a few inches away from and forward to catch air as it is deflected off flat surface of bumper and force it into radiator/grill area,

Or, cut 2 6"x6" sections out in face of bumper then welding in 3/8" x 1" x 6"- to box/reinforce opening.

I also think the round brush guard is causing way too much air separation, thinking of using same setup as the old military blazer had.

Anyway, I am open to other ideas.