My 2000 (195k miles) has been needing to have coolant added about every 3000 miles for the past 9 months. I was thinking it was just normal leaking for an old vehicle and thought nothing of it. Then recently it started to have a shake/misfire for about the first 20 seconds after starting up, but it would then run fine except for noticeably more cloudiness coming from the exhaust for a couple miles, bit then it would go away.

One afternoon it wouldn't start at all - wouldn't even try to crank as if it were hydro locked. Gave up that evening in frustration and hand turned the crankshaft the next day and it then it started no problem - except for the normal early stumble and what again appeared to be steam from the exhaust. Checked the oil and it doesn't show any milkiness on the dipstick.

It refused to start again a week later in yet another apparent hydro lock. Waited another week when I had time to turn it again and it was still locked. Hauled it to a friend's shop and once again turned the engine by hand and it started normally. So we then tested the coolant system for a pressure leak and had a very subtle drop. Pulled the spark plugs and found nothing wrong there. Checked cylinder pressure with a kit and found nothing alarming (between 3%-8% leakage on 90psi), so I feel like the heads and gaskets are in good shape.

I changed the intake manifold gaskets around 2009 when there was an coolant leak showing externally, so they're not factory gaskets. That said, does it sound like that would be the problem area again? Any other suggestions? All the searches I've found show a leak showing externally and not into the cylinders.

Really hoping to get it resolved as I have really loved driving this thing through the years. Thanks for any help!

 

Refusing to crank until engine is turned by hand sounds like a starter problem to me. I wouldn't think you would be able to turn a hydro-locked engine by hand. Usually engines that leak coolant past head gasket or through cracks into the cylinders are much worse when warmed up and yours gets better. Cylinders that have coolant leaking into them have spark plugs that look significantly different - steam cleaned! If you have a leakdown rate of 3-8%, then your rings and valves are fantastic for nearly 200,000 miles - keep that engine if possible. Probably you was looking for bubbles in cooling system at the thermostat when each cylinder was pressurized? What was the result? Certainly the intake could be leaking again into an intake port (and not into the oil), but that would be a bit more uncommon. Any water getting into a cylinder would cause copious amounts of white billowing smoke. Too much water and the cylinder starts to misfire.

 

This is why I haven't been quick to change the gaskets just yet.

The starter turns with no issue whenever I hadn't let it sit for awhile (and in theory allowing the coolant to slowly bleed into an intake port). But when it does lock, it turns a bit before having a nasty clunk. I haven't ruled out a starter issue, but it seems to not be a root problem to me. And the hand cranking is not easy either before freeing up (I know - how can you possibly turn a hydro locked engine by hand?!).

I hadn't thought of checking for bubbles at the thermostat during cylinder pressure checking. Will definitely do that next. If that checks fine, then I guess we'll go ahead and change the intake gaskets. While I bring that up, does that job require replacing both upper and lower intake gaskets? Probably do them both while it's apart, but couldn't remember if it required disassembling that whole throttle assembly or if it can come out in one. Thanks again!

 

How's the oil in the pan looking when you pull the dipstick?

Any goo? Brown? Foamy oil?

 

Doesn't require it, but upper gaskets will come with the set for the lower so why not do them both! I think that upper intake is super easy to R&R. You can leave the throttle body mounted on it if you like - but it's up to you.

Of course, using the Felpro metal/rubber premium intake gaskets is advised.

Don't forget to chase the bolt holes in the heads with a tap (especially clean out the bottom of the ones that don't go through) and to wire brush the intake bolts - then apply Teflon sealer (like for head bolts) and torque in proper sequence with an actual inch.pound torque wrench. I like to let them sit overnight and then go over them one more time before I cover up that one front bolt with the A/C bracket.

Good luck and best wishes for a successful repair

 

Oil looks fine. Finished up late last night so just now able to post. Started to tear down to replace intake gaskets but checked for bubbles in the coolant first. Did 3 of the cylinders and had bubbles in all of them. One of them was a bit more vigorous - but still only had a leak down of about 4%. So we put the pressure on the radiator again and turned the engine a few times and sure enough had coolant slowly flowing out the spark plug hole in that one cylinder. So mystery solved. So that's the project for the next week.

But this really confuses me in the fact that every indication on the leak down test shows the heads and gaskets are fine. We even tested it out and made sure the gauges were accurate. Kinda odd, but obviously the cylinder leak down test isn't a tell all, just a general indicator.

Once again, thanks for your input.

 

Leak down test results are only to evaluate leakage of air past rings and valves. The 4% is the pressure drop occurring from flow across a 0.040 orifice into the cylinder at 100 psi. Has nothing to do with coolant or coolant leaks. However pressurizing the cylinder with the apparatus can force air past bad head gaskets or cracks into the cooling system that show up as bubbles. So you can use the test apparatus for a second purpose. It's just that the 4% doesn't mean anything for what you are trying to test. In fact, having coolant in the cylinder could make the leak down rate artificially low since coolant would not go past rings/valves as easily as air would.