I have a 2000 3.0 XLT (120k miles) that started showing signs of coolant in the oil in 2020, and it seemed to get worse quickly, and it's been mostly parked ever since. For many years it also had the classic timing cover coolant leak that I managed by just topping off the coolant when needed. Obviously, once I started seeing coolant in the oil I assumed that the gasket on the other side of coolant passage had given way. So, reluctantly, I tore apart the front of the engine and got a new timing cover and water pump and gaskets all around. Replacing the timing cover and gasket did fix the external coolant leak that used to drip from the left side of the timing cover. However, I was still seeing huge amounts of coolant in the oil.

So, here I am today trying to figure out where to go next. I did a compression test and got the following results (the engine was not warmed up):

Cylinder 1: 125 Dry, 143 Wet
Cylinder 2: 111 Dry, 134 Wet
Cylinder 3: 115 Dry, 138 Wet
Cylinder 4: 128 Dry
Cylinder 5: 125 Dry
Cylinder 6: 125 Dry
Wet = 6 mL of oil (about 1.2 tsp)

As you can see I didn't perform the wet test all the way around, I figured I'd see how the two lower cylinders, 3 and 2, would respond - and then do it on one of the "good" cylinders, cylinder 1, as a reference point. Should I have done them all wet as well?

Are these readings enough to diagnose a head gasket? I had assumed that if it was a head gasket I had hoped to see an obvious, more drastic, reduction in compression, like 30-40 psi less than the others or something like that. But 10-15 psi less doesn't seem like a huge difference, although it's obviously telling that they are adjacent cylinders.

I'm looking for advice on where to go next. If you didn't figure it out by now, I'm not an expert mechanic or anything; just your average home mechanic, so go easy on me haha.

 

Welcome to the forum

3.0l Vulcan engine runs 9.3:1 compression ratio so expected static test should be 160psi
But since you have an average of 125psi either low battery(cranking speed) or the compression gauge is not calibrated, which most are not, lol

Adjacent cylinders with lower compression can be tricky, assuming all spark plugs were out for the test I would expect a bigger drop for burnt exhaust valves or blown head gasket between two cylinders
If you were only removing 1 spark plug for the test of that cylinder then that could explain the 125psi and the lower than expected drop in a leaking cylinder

Certainly an issue with 2 and 3
Coolant in the oil is pretty bad, shouldn't run the engine that way of course
The bearings get very hot, not enough to turn coolant to STEAM which washes away ALL the oil in the bearing at that moment...............so spun bearings

I can think of only 3 ways coolant can get into the oil on a 3.0l
Front cover water pump passages
Lower intake manifold, 4 corners
Blown head gasket

 

The battery was new last year, but then sat and was drained completely. I used a "repair" setting on a battery tender which brought it back to life, but it is possible that the battery is compromised and doesn't produce as much amperage as before.

I did remember to have all spark plugs out for the test.

I'm hoping I did a good enough job replacing the front cover that it can rule out that possibility (hopefully). Do you think it's worth starting to tear off the intake manifold and see what I find, and then move on to the heads if I don't find anything prior? Or is there something else I can do to pin point this issue?

Thanks for all your help.

 

Coolant leaking into a cylinder will cause the spark plug tips to stay WHITE, steam cleaned, where the other cylinders will be light brown
Do you remember that when you took out the old spark plugs?

Another trick is to unplug fuel pump relay or fuel pump fuse, then start the engine and let it run out of gas
Remove radiator cap
Remove #2 and #3 spark plugs
Get a piece of paper to hold in front of 2 and 3 spark plugs holes
Have some one Crank the engine over, it won't start, no fuel
If paper shows fluid coming out.......................coolant is leaking into one or both of those cylinders

 

To be honest, all the spark plugs look mostly the same to me. Nothing very obvious there. Also, throughout this whole process, it has never been super evident that I'm burning coolant. It just seems to end up in my oil somehow. Any white "smoke" I get out of the exhaust usually seems to be condensation, but it's hard to say with certainty.

I will give that test a go - I still have all the spark plugs removed from performing the compression test, do I need to put them all back in except for #2 and #3, or is it fine if they are all removed still? And just out of curiosity, what effect does removing the radiator cap do?

Thanks again for your guidance. I really appreciate it.

 

Removing the rad cap allows coolant to flow downhill, into any openings that are not part of the cooling system
All spark plugs can be out, you are looking for any cylinders that are discharging anything but air, assuming 0psi fuel pressure

Yes, symptoms don't read like a cracked head or blown head gasket, except for the lower pressure in 2 and 3
But next stop would be lower intake so best to take these off the table

 

I did that test with #2 and #3 and didn't see anything on the paper towel. I suppose tomorrow I'll try the rest of the cylinders just to be sure.

 

Looks good, but not sure why the lower compression