Lower intake manifold question

1996 windstar, 3.8, 147,000 miles. I have had the car since new. I have a coolant loss again. No obvious leaks, no OBD codes come up. The first time this happened, I replaced the head gaskets and lower/upper intake manifold gaskets. My engine builder rebuilt the heads, and told me the coolant loss came from the coolant passages in the lower intake manifold, leaking through the gaskets. I read that Ford updated the lower intake manifold - anyone have any information on this? Also Felpro (and I think Ford) list a 3mm thick and a 4mm. thick lower intake manifold gasket. What is best for this repair, if I change the gaskets again?

Thanks for your replies, and thanks to the regular contributors for some excellent and reliable info on the Windstar in the past.

1996 windstar, 3.8, 147,000 miles. I have had the car since new. I have a coolant loss again. No obvious leaks, no OBD codes come up. The first time this happened, I replaced the head gaskets and lower/upper intake manifold gaskets. My engine builder rebuilt the heads, and told me the coolant loss came from the coolant passages in the lower intake manifold, leaking through the gaskets. I read that Ford updated the lower intake manifold - anyone have any information on this? Also Felpro (and I think Ford) list a 3mm thick and a 4mm. thick lower intake manifold gasket. What is best for this repair, if I change the gaskets again?

Thanks for your replies, and thanks to the regular contributors for some excellent and reliable info on the Windstar in the past.

I would rent a coolant psi tester from AutoZone. It will allow you to put psi on your cooling system without the engine running so you can look for leaks.

Sorry I don't have any answers on the gaskets. I do know that gaskets have been an issue for all auto makers. I think they're trying to get by too cheep and we are paying the price down the road. Also, cast iron and Alum expand at different rates causing rubbing on the gasket surface.

Regards
Dan

Let me shed some light on what I ran into on the 3.1 Liter Chevy V6 engine. This engine ( 3.1 L ) along with the 3.4 liter gm v6 has been notorious for intake gaskets failing but as it turned out on mine, the intake gasket mounting bolts had loosened up and alllowed the coolant to leak into the engine. So before you tear everything apart you may want to try and retorque all of your lower intake manifold mounting bolts to specs and if you find they are loose put some threat locker ( medium strength ) on the bolts which is what i ended up doing. I wish I had done the torque check first it would have saved me a lot of work. I did all of the intake manifold removal procedure which was very time consuming on this motor (20 some hours )myself and found out it was just loose mounting bolts causing the problem. The gaskets were fine upon removal of the intake manifold. I replaced them anyway with the so called improved gaskets from the local Chevy garage. Luckily no damage resulted to the engine due to the coolant in the oil. In some of these engines the coolant in the oil caused the camshaft bearings to fail and caused the camshaft to snap in half which results in the purchase of a new motor. Well good luck and let me know what you find. Oh by the way this leak started out very slow ( about a pint a month ) and gradually if failed all at once one night for my wife on the interstate. Luckily she pulled over and shut if off when the temp gauge went up. After repairing this motor 6 months later the tranny crapped out. Got it fixed then I unloaded this car after acquiring a 1996 Buick Regal from my dad which is definietely a lot better car and engine ( 3.8 Liter ) than the 1995 Monte Carlo with the 3.1 Liter motor. I have not had a issue with my 98 Windstar as far as the engine goes ( its got the 3.0 L motor )