Help connecting hoses

5/8" hose is the pressure inlet, 3/4" is the outlet.

The flow cutoff valve goes on the inlet hose, since it should have 5/8" hose nipples to fit.

The 3/4" line goes to water pump suction side, or radiator, or...IIRC, and I might be wrong here, but I think your 3.8L has 3 suction connections on the water pump. One, obviously the huge one from the radiator. One straight up and one at an angle toward passenger side. The top one should be the bypass line from the thermostat housing. The angled one is the hose from the heater core (3/4"). Someone with Buick 3.8 experience can help me out here, obviously.

Key thing is, you don't want restrictions on the outlet of the water pump. You need to restrict the inlet side to ensure the water pressure from the pump doesn't blow out the heater core. Even non-A/C cars have restrictor nipples or something to ensure you don't break stuff.

It APPEARS all you may have to do is take out that connector where your hand is and plug the 5/8" hose on the 5/8" heater core inlet connection, and 3/4" hose to the heater core return to water pump port.

Here's a diagram from the 85 Cutlass CSM with 3.8L. Maybe this can shed some light.

In the pictures you provided you can clearly see the two nipples for the heater core. Both are capped, the one cap, the larger one, says "20" on it, and the smaller seems to be unmarked.

The tube with the 20 cap is the larger, 3/4" tube and takes the 3/4 hose. The smaller unmarked cap is on the 5/8" tube. The existing hoses themselves will tell you to a certain degree where they ought to go,. After that, the diagram showing what goes where should get you done.

The only other thing here is that, if your bypass has been there in the circuit for a while or the engine has been sitting, you might want to pay a trip to your local automotive supply shop and pick up some new heater hose in 3/4 and 5/8 ths. They should sell it either in bult, by the foot, or in a pre-cut length in a package or bag. Add a few hose clamps in there as well; they like to strip out just as you think that they are tight.

Why change the hose? UV, heat and cold and chemicals and additives in the coolant can all combine to "eat" the rubber and cause it to fail. Since it is the inner layer that gets the most damage, you tend not to see the deterioraton until the hose pops, usually on the interstate in the middle of nowhere at 2.30 on a Sunday night!


Nick