Cylinder 6 misfire and coolant loss

[FindingPhaedrus]

2000 Ford Explorer XLS - 4.0L V-6; ~110K miles
Symptoms:
- Intermittent cylinder 6 misfire (throws code)
- Intermittent rough start lasts ~15 seconds, then idles smoothly; does this on days that are not rainy/humid also, but humid days are worst.
- Regular coolant loss. Sometimes considerable (1/2 reservoir in 1-2 weeks); sometimes considerably less (1/4" loss over a week). Driving distance doesn't seem to make a difference. No evidence of leak.
- No obvious symptoms of head gasket issues (whitish color to oil, thicker/stickier viscosity, sweet smelling exhaust)

What's been done:
- Cooling system pressure check
- New coil pack
- New radiator
- Recent tune up

 

[RomeovilleIL]

Start the truck, run for maybe a minute or so then turn off. Pull the #6 plug. It will probably be wet with radiator fluid. Gasket leak or cracked head does not always mix fluids. It's fairly common leak area between 5 & 6. Compression test can verify this as well. Coolant is bogging the cylinder until it gets hot enough that it comes out the leak as steam instead of liquid.

What can you do to fix... Well, the proper thing is to pull the head and have it checked for cracks and possibly remachined, more likely replaced, and install new gasket. Repair does not require pulling the engine from the truck.

Other people have had good results using some of the permanent leakstop/block sealer products that are poured in, run, then flushed -- follow directions carefully. Be aware that its not a guaranteed fix and will make things messy/hard to clean later if you decide to pull the heads and fix the right way. Don't use the temporary sealer products (anything that the bottle tells you can be left in the system). They will eventually fail while gunking up and clogging other parts in the cooling system along the way.

 

[2000SportDennis]

I would reccomend a compression test also.

I had similar trouble with mine when I bought it with 108,000 miles on it. About a week after i bought it i was getting misfires in 3 & 4, frimarily on startup, and when accelerating harder such as highway entrance ramp. First thing i thought was pluggs, replaced them(and wires) and that worked for about a month then the same issue came back. Replaced coil next and another set of plugs with it. Again worked for about a month. Had been losing about 1/2" coolant per week. So next I determined i would replace head gaskets, when i took heads off i had them pressure tested and come to find both of the heads were cracked. Cylindars 3 & 4.

I really hope this isn't the case for you, but figured I'd share this because it sounds pretty similar. I never had evidence of moisture in oil or wierd smell either.