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WHY 2 oil sending units?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by MudNurI, Feb 26, 2002.

  1. MudNurI

    MudNurI 1/2 ton status

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    Okay I'll try to explain this the best I can--

    today while putting some finishing touches on MudNurI--- we were getting ready to change the oil sending unit- (it was leaking we suspect)... so we pull off the air cleaner- I hop ontop of the motor, and WHAT do I see? TWO oil sending units, a small one- and a VERY large one. both of them had factory hook-ups.... etc... however there was only 1 oil pressure gauge... so I head down to the local parts store, to get both replaced.... walk in, tell the guy 86 K5, 305- and, WHY is there two of these- he first asks me-- "thats fuel injected?".. NO sir, thats carborated... "does that have a oil pressure light or guage"... guage...hmmmmmmmm flipping through the books etc.. finally tells me its "fuel cut off switch".... "its a heat choke switch" (WTF is that?).... etc... so needless to say- I said "give me both"... and replaced both of them... but my question to you guys- WTF is up with 2 of them? Totally baffled myself, John, and the guy I bought the truck from....?????any idea's?

    Brandy

    HELP!!!!! I need 16.5x 12 rims -------please please please!!!!!

    oh, still LOVING the new dmax as well!
     
  2. pcorssmit

    pcorssmit 1/2 ton status

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    The FI trucks use 1 for the gauge (mounted on the side, near the filter), and one on the top, that is a fail safe when the fuel pump relay dies (sends power to the pump when you build up oil pressure). Don't know why a carb'd truck would have 2, but it wouldn't be for the same reason an a FI truck (mechanical vs. elec. pumps).

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  3. jimmyjack

    jimmyjack 1/2 ton status

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    My 83 has two. One on the back of the block in back of the intake, the other is near/ above the oil filter. The one is a sending unit, the other is an oil guage switch. They were both leaking like hell. I went to Autozone and almost choked the pimple faced geek behind the counter when he told I didnt know what I was talking about. Don't know what either one does to compliment the other, but I replaced them both!

    That jeep thing? Yah I understand it....... Like my Blazer? <a target="_blank" href=http://community.webshots.com/user/blazerk5>http://community.webshots.com/user/blazerk5</a>
    Jim
     
  4. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    I believe this is the info you're looking for:

    The unit at the back of the block is the sender that's hooked to the oil pressure gauge. It senses the oil pressure in the engine and translates it to an electrical current that translates to a reading on the gauge in youre dash.

    The unit above the oil filter is an oil pressure switch that is connected to your electric choke system. If the switch doesn't read oil pressure at start-up, the choke won't engage and your truck won't start. It's like a built in safety feature to save your motor....

    I'm sure there's a little more to the oil pressure switch system, and if Grim reads this you can expecty a better technical explanation.....OH GRIIIIIIII-IIIIIM, WHERE ARE YOU???!!![​IMG]



    <font color=red>DIGGING AND DIGGING AND DIGGING</font color=red>
     
  5. MudNurI

    MudNurI 1/2 ton status

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    well I am glad someone else had them leaking!! we can't tell what one was leaking- it hasnt been run in 9 month's.... but we do know one of them was- i think the only way to go was to change them both- at 20 bucks a pop- its not that expensive!....I know the feeling of the pimple headed freak!! the guy I spoke to didnt know what company they use for exhaust parts either- when I went in today- I had to order new header collectors- because when the exhaust was done, they put them on wrong- and now need to be replaced (melted a sneaker of a back seat passenger- and thats with a 3' body lift!).... oh the joys of getting it on the road!

    thanks guys!
    Brandy

    HELP!!!!! I need 16.5x 12 rims -------please please please!!!!!

    oh, still LOVING the new dmax as well!
     
  6. TorkDSR

    TorkDSR 1/2 ton status

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    could one be for the gauge and one be for the "look stupid you have no oil pressure" light?

    it doesnt make sense, but it makes sense....you know?[​IMG]


    beligerence doesn't justify intelligence.
    <font color=blue>wheelers hate posers.</font color=blue>
    <font color=red>79k15/400/700r4/205/38.5</font color=red>
     
  7. newyorkin

    newyorkin 1 ton status

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    I had always thought the second one on FI trucks was a low/zero pressure cut off, like the one Canmore described, only it cut power to the pump when there was no oil pres. Fuel cutoff switch I think it's called in FI.

    Ratch
    CK5 album &lt;-- New Wheelin' pics!
    This is not a new signature.
     
  8. SAVAGE1

    SAVAGE1 1/2 ton status

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    I was doing some research on this exact same subject. I just dropped in a new crate engine and I'm installing a ProComp mechanical oil pressure guage. Should I plug it in to the port on the back of the intake manifold or to the one near the oil pump? I already test fitted it to the intake but just wanted to make sure.

    Rod
    Alameda, CA
    85 K5 6"ProComp 35"Boggers 14Bolt/ Dana44 4.10's
    <a target="_blank" href=http://coloradok5.com/gallery/K5Jungle>http://coloradok5.com/gallery/K5Jungle</a>
     
  9. MudNurI

    MudNurI 1/2 ton status

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    the only problem with the fuel cutoff switch thing is I am not Fuel injected...


    and up another post- ( so i dont reply twice)
    it can't be a "stupid you have no oil light" ... I don't have one of those either LOL!!

    thanks though- im waiting for Mr. Reaper's technical expertise to be able to tell John and Roy in "man talk" what it is LOL

    Brandy

    HELP!!!!! I need 16.5x 12 rims -------please please please!!!!!

    oh, still LOVING the new dmax as well!
     
  10. pcorssmit

    pcorssmit 1/2 ton status

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    <blockquote><font class="small">In reply to:</font><hr>

    Originally posted by newyorkin
    had always thought the second one on FI trucks was a low/zero pressure cut off, like the one Canmore described, only it cut power to the pump when there was no oil pres. Fuel cutoff switch I think it's called in FI.


    <hr></blockquote>

    I've heard that from a lot of people as well. Unfortunatly, they're all wrong. [​IMG]

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    One is for the gauge, one is for the electric choke. Without oil pressure, the choke doesn't work. The truck will run, it just won't have an electrically heated choke.


    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>www.dorianyeager.com/index2.html</a>
    Why insist on counting when the ring gear has the tooth counts stamped in?
     

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