91 Buick Regal using coolant

I would be looking at the intake a bit closer. That would be my first guess. Also look around the throtle body area. It might be leaking down but buring off before hitting the ground.

A pressure test should give you a pretty good idea of where the coolent is going to. With engine OFF pressurize the system and look carefully for leaks... if you suspect the heater core, place a white paper towel on the passenger side floor board and see if it picks up any antifreeze from the carpet or droplets from the heater core.

If it has the plastic upper intake manifold plenum, chances are pretty good that it's leaking at the rear of the plenum by the throttle body ...kinda hard to see.

That engine doesn't have the plenum problems that plague later versions. Still, the intake gaskets are a possibility. I bought a good quality core engine from a junk yard to rebuild for eventual transplant into my Reatta, and was surprised that the intake gasket was not in good shape.

On the Reatta, I also found a leak at the water hose neck on top of the engine. It has a large O-ring which was pinched and would leak slightly when hot.

Seeping freeze plugs are another possiblity

Check for the obvious:

Radiator cap. Radiator. Hoses. Heater Core. Water Pump. Intake Manifold / Head Gasket. and the Freeze Plugs.

Having a 91Pontiac with a 3800 I've replaced everything but the Freeze plugs and head gasket. The freeze plug behind the coil pack is starting to leak a little now.

You didn't say what the mileage is on your car. My intake gasket began to leak externally on the driver side of the engine at 220,000 miles.

Are you leaving puddles of antifreeze on the ground?

How much coolant are you using? How much do you add in a week?

Good Luck.

Harryface

The car has 350000 km's on it. I've checked all the obvious visual inspections. I guess I wouldnt see it if it was on the back of the manifold. Its not leaving any leaks that i noticed. Tonight Ill put a piece of cardboard under it when Im done driving it, see if it leaks a bit after shut off. As long as where sure that the 91's didnt have that plastic plenum, we can move on.

Is it possible that the intake manifold gasket is leaking coolant into the cylindres slowly, burning off, leaving no white smoke or residue on the plugs? Im pretty sure my heater core isnt leaking, but Ill check more closely.

Thanx

Damn right, it is possible. A slight leak can leave little evidence. I wish I had kept the photos of the gaskets I took off my rebuild core.

And these are NOT the worse that GM has used.

I had a '93 Olds with a 3.8L that had a tiny coolant leak. I looked for it for months till I found it. On my engine, there was a small hose that went from the water pump to a connection just under the intake manifold. That connection was a plastic nipple that threaded into the block/head (forget which), and it had a tiny crack in it. The replacement part at Pep Boys was about $5 and made of steel.

doug

doug

Believe it or not, GM actually used a metal bypass tube in 91.

Harryface