[1999montana]

Two things:

1. I noticed that our van was rattling a bit more than usual in the spring.

2. When I changed the oil, I discovered a small amount of antifreeze in the oil pan that came out as a 'blob' at the end of the drain cycle.

I knew I had a coolant leak, but it was quite minor. On highway use, the engine sounded 'looser' than normal and this fact urged me on to change the oil.

To explain. The engine has always had this ticking lifter or piston slap in the morning. It started at about 30,000 Kms. After about 5 minutes or so, it would go away. I associated this with piston slap due to the design of the piston and a short skirt that causes the piston to rattle in the bore.

From past experience, I've heard sticky hydraulic lifters too, but generally they don't go away since the plunger in the lifter is usually bottomed out and won't return to normal height due to varnish and valve spring loads.

Anyway, I drained the oil in the van as I mentioned. I added Rislone and 10w30 as opposed to 5w30. I figured with 180,000+ Kms, there was sufficient clearance between moving parts and bearings to allow the thicker oil to be used.

Then, I drained some coolant from the rad and added a stop leak additive designed NOT to clog the rad. It sealed a problem with the intake and may have also temporarily sealed a leaky head gasket on cylinder #1.

Why did I do this? The van has already had the LIM gasket repair replaced twice (actually I think my GM dealer only put tabs in the coolant the second time and pocketed the money).

We don't want to spend any more money on it, and I am pretty good at listening to and analyzing the various problems the van has; - fixing them before they become big issues.

Bottom line; - the engine runs smoother, the rattle is gone and there is no evidence of a coolant leak.

So why did I tell you this?

Since you are running a 2001, you may want to investigate whether there is reason to believe that oil and coolant are mixing together. The result could cause the lifter problem you mention.