Auxiliary fan - purpose.

[east302]

Here’s what controls the auxiliary fan...

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[Pinger]

Great post HWB, thanks - and thanks too to the other posters - great info from all of you.

You probably figured out I like talking about trucks!
Hey what else are we supposed to do during lockdown? Work on em or talk about em

Just picked out the above bit because it chimes with something that occurred to me yesterday after I'd logged off. You guys write really well - and it makes a huge difference. I know I come back at you all with more questions but I never have to ask 'what did you mean by that?'. You explain things brilliantly.

Quick question that may shed light on my trucks reluctance to fire up on gasoline. When you turn the key to start up your trucks - how much cranking does it take before it fires up? Mine - even when starting reliably - takes maybe 3-4 seconds before firing. Are yours the same?

 

[east302]

Quick question that may shed light on my trucks reluctance to fire up on gasoline. When you turn the key to start up your trucks - how much cranking does it take before it fires up? Mine - even when starting reliably - takes maybe 3-4 seconds before firing. Are yours the same?

I have two 98s and they both start within one-two seconds.

Longer crank time could point to a fuel issue, check pressure with ignition on/engine off. Spec for a 350 vortec is 60-66 psi.

In case you haven’t seen them, PDF scans for some factory manuals up to 1998 are here:


https://www.gmt400.com/threads/88-95-service-manuals.43575/

The fuel system diagnostic is buried in there somewhere, I think volume 3 for 1998 at least. I usually just use alldatadiy.com as it’s the same information from the manual and easier to navigate.

 

[KRS1]

Right on guys, I am going to keep a eye out for one of those aux fans at the yard! It will have all the correctly sized brackets etc which is a huge bonus. It looks like the VCM controls the fan it so maybe that can be incorporated into the wiring, or at least it's relay..

 

[HotWheelsBurban]

Me too! In Houston summer heat, l think one of these would be helpful. My truck hasn't overheated except for that one time (in January LOL)but I know why that was. Soon I hope to be able to get to the treasure yard to hunt for truck goodies. This fan is something else that I learned about on this forum, and now I want to do this mod too.

 

[HotWheelsBurban]

My truck starts within a couple seconds, ever since I has the Passlock neutered. I would look at the fuel pressure too. There's a test port behind the throttle body on the driver's side of the intake manifold. Has a Schrader cap like the air conditioning lines.

 

[alpinecrick]

Quick question that may shed light on my trucks reluctance to fire up on gasoline. When you turn the key to start up your trucks - how much cranking does it take before it fires up? Mine - even when starting reliably - takes maybe 3-4 seconds before firing. Are yours the same?

What east302 said......

All four of my Vortecs start with a bump of the key unless I leave them outside in single digit weather or colder. Then it takes an extra revolution of the motor.

 

[alpinecrick]

Although I have heard they exist, I've never seen a GMT400 with the factory auxiliary fan on it. I'm guessing it was probably limited to the SUV's.

 

[alpinecrick]

In pinger's photo and east302's diagram, the auxiliary fan goes in the same location and same bolt holes as the external trans cooler on the GMT400's I've seen. May have been an export deal.......?

 

[Pinger]

In pinger's photo and east302's diagram, the auxiliary fan goes in the same location and same bolt holes as the external trans cooler on the GMT400's I've seen. May have been an export deal.......?

Bear in mind that my aux fan mounted directly to the AC rad and East 302's piece refers to the fan being triggered by either or engine or AC temps.
If that is normally where a trans cooler would be (with AC present) then there's be three rads one behind then other behind the other. Is passenger side fitment of trans cooler only with no AC? I'm guessing (by what's been said) that my trans cooler isn't one GM made or specified. Odd to take it to the opposite side from where the pipes exit and enter the trans but that would be true also of the AC rad if it were driver side - given where its plumbing passes through the bulkhead into the cabin.