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  1. #1

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    p/s pump & rusted cooling lines on 91 3.1 Gran Prix

    Replaced engine wiring looms on Gran Prix with 3.1 (vin T). while pulling return line off power steering pump the plastic nipple broke off pump. will pump off any 89 to 94 cutlass, lumina, regal or gran prix with the 3.1 T engine work. want to try and get the lowest mileage pump at the junk yard.
    Also, on the metal cooling lines supplying the heater core. First off, is the heated coolant to the bottom of the throttle body needed. Why does it need heat when there isn't any liquid there? I'm in KC where temperatures range from 0 in winter to 100+ in summer
    When we got the Gran Prix, the previous owner had already modified the metal pipe running from the heater core across the firewall, down along the frame forward and back up next to ecm ending with rubber hose which then connects to the top of the water pump. The metal must have rusted through where the brackets hold it against frame. he had cut the pipe up by the turn going across the firewall and clamped and long piece of heater hose to the pipe to the water pump. i tried to find one at junkyard, but they were all rusted or had also been modified. i take it this is a common problem on this engine or body model????
    I was wondering if i could plumb the throttle body piping with the heater piping in series to eliminate this rusty firewall pipe completely. to clarify: (1) existing plumbing runs from under thermostat to throttle body, (2) fabricated plumbing from throttle body to heater core, (3) fabricated plumbing from core to existing return line used for throttle body return to water pump.
    Or can i just eliminate the water supply to the throttle body?
    Maybe I'm just paranoid from 20 years of working with tractor trailers, but the less rubber hose specifically and external plumbing generally a vehicle has carrying coolant the less chance of breakdown and reduced maintenance.

    Any thoughts on any of this is appreciated.

  2. #2
    Robby1870's Avatar
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    p/s pump & rusted cooling lines on 91 3.1 Gran Prix

    Im not sure about your plumbing questions, but any p/s pump off a 3.1 (T) will work.

    Robby
    Robby Whitesell
    2006 Pontiac G6 GT - 3500 V6

    1985 Toyota Pickup DLX - 2WD - 2.4L I4

  3. #3

    p/s pump & rusted cooling lines on 91 3.1 Gran Prix

    the plastic nipple is part of the resivuor, not the pump, they come apart. As for the coolant, the TB is on the bypass line, once the thermostat opens the bypass line closes.

  4. #4

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    p/s pump & rusted cooling lines on 91 3.1 Gran Prix

    are u saying both of those lines under the thermostat don't have water flowing out of them when thermostat opens? then that would mean that no coolant would be going to the heater core.

  5. #5

    p/s pump & rusted cooling lines on 91 3.1 Gran Prix

    Lets see, there are 3 paths for coolant, the rad hose, the bypass line which passes through the TB, and the heater core. The heater core is always on, nothing but open passages from the pump to it. The bypass line is regulated by the valve on the rear side of the thermostat, when the thermostat opens, the bypass line through the TB gets blocked off.

  6. #6

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    p/s pump & rusted cooling lines on 91 3.1 Gran Prix

    sorry if i am being stupid on this.
    on the intake manifold, under the thermostat, there is a pipe bolted on that points forward and then turns straight back under the manifold and then points up to the rubber hose that connects to TB. water returns to water pump through long pipe running across front of forward rocker cover.
    where is there a "valve" located in this?
    the only thing i see which might be a valve is a fitting screwing into intake manifold opposite the bypass outlet under the thermostat. it must have some kind of o-ring or seal and a tanged lock u squeeze to remove the metal pipe which eventually supplies water to the heater core. But as you say there shouldn't be any valve in heater core plumbing.

  7. #7

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    p/s pump & rusted cooling lines on 91 3.1 Gran Prix

    i found an article at 60degreev6.com which talks about eliminating the coolant flow to the throttle body.

    http://www.60degreev6.com/index.php?p=pages&pid=68

    there is also a picture of his car with the bypass.

    http://www.60degreev6.com/index.php?p=pages&pid=20

  8. #8

    p/s pump & rusted cooling lines on 91 3.1 Gran Prix

    You're right, the heater core has no valves anywhere in its lines, its always on. I would imagine when the thermostat opens there is a pressure drop and there is slightly less coolant going through the core.

    And for the bypassing the throttle body, that is something different. The TB is placed in the bypass line, taking the TB out of the loop does nothing, the bypass line is still hooked up and working. The idea behind the coolant to the TB is for very cold conditions when the throttle may stick/freeze partially or fully open.

    For the bypass line, pull out your thermostat. Look down into the intake manifold, see the hole that would be under the thermo, that is the opening to the bypass line. Now look at the bottom of the thermo, see the valve thing that isn't on most normal thermostats, that is the valve that closes off the bypass line. My memory of the 3.1 is slightly fuzzy, but I know most new GM engines are set up this way.

    The idea behind the bypass line is to keep a good amount of coolant always flowing through the engine to decrease the likelyhood of hot spots. When the thermostat opens you want coolant to flow into the radiator and not cycled through the engine, so the bypass line is shut off. Now if you blocked either the heater core or bypass line off, and ran the heater core hoses like you mentioned, you would be flowing a very small amount of coolant through the engine (the heater core has a huge pressure loss, having the heater core line as the only return line for coolant with the thermo closed would provide almost no flow through the engine) and you may run into improper cooling situations and/or hot spots when the thermostat isn't open. If you had some other coolant tap on the engine (like the oil cooler on the TGP and 91-93 DOHC's) you may be able to get away with blocking off one of the lines cause the coolant would just go through the oil cooler instead. The whole idea behind the extra bypass line is to keep the coolant flowing through the engine.

  9. #9

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    p/s pump & rusted cooling lines on 91 3.1 Gran Prix

    lol! I know about that heater line rusting and blowing out though! Mine went last summer and I lost all my coolant up a mountain, had to coast 20 kilometres downhill to the nearest station... a funny experience, to say the least. I had to get my replacement from the dealer, as everyone else said just to use rubber hose. Personally if that line needs to be replaced, I'd recommend getting the whole assembly. There's an awful lot of tight turns in that plumbing, and it just seems kind of susceptible to kinks. It wasn't too expensive, $75 CDN.
    Mike<br /><br />1980 Chevrolet Monte Carlo<br />1991 Chevrolet Lumina Euro 3.1

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