1999 Explorer 4.0 SOHC,P0304, bubbling and gas smell in cooling system

[rgurleyjr]

First time post. This will be long, but really need some help. Note that 2 months ago, her son did a complete tuneup, new plugs and wires.
Our church bought a 99 Explorer for a lady who hit hard times with her health and could not work. Other than little stuff, it ran good for 6 months or so. Just last Sunday, she said it wasn't running right and wanted to stall, shaking, etc. The truck was still warm, so I started it and there was a noticable misfire at idle. The only code was P0304. I did not drive it, just told her I'd come back the next day.
The next day on Monday, I pulled the #4 plug and it was sort of red/rusty looking while another plug was still new looking. I also noticed that it ran fine when cold, but within a few minutes of running is when it started missing. Also the coolant reservior and radiator smell of gas/combustion smell. Also after running for a while, there was consistent bubbling in the reservior. No white smoke, but the tailpipe is very clean inside. I filled up the radiator and reservior and told her I'd do research and get back with her, her cooling system was low
Well, the whole time until today when she dropped it off at my house, I thought she had a OHV, not SOHC. So this week, I did a bunch of research on this site and others about OHV explorers and my symptoms above. I was convinced her problem was the lower intake gasket leaking coolant into the combustion chamber as that is a problem after much reading. BUT.....now that I see its a SOHC, it appears that no coolant goes through the lower intake at least per someone on this site.
So with all of that said, this appears to be a head gasket or head problem, right? I have never owned a ford with the 4.0 engine. I also read just now about these engines and timing chain nightmares. If the above does indeed sound like a head gasket or head, is it super hard/not a good idea to try and fix it in regards to the problems with the chains? I have not done a compression check yet because I thought it was a leaking intake gasket and didn't see the point. Any help or confirmation would be appreciated.

 

[J_C]

I'm wondering if it's just a clogged fuel injector, that the other observations might be coincidental. Is it possible that # 4 plug was in a hard to get to spot and the guy didn't change it? Do you know for sure that it's going through coolant now or could it have been low for a while?

It seems kind of funny to me to buy a gas guzzling semi-high maintenance older SUV for a (presumably single) woman having hard times. I would've looked for something more along the lines of a 2001 Ford Focus.

 

[rgurleyjr]

Our small church couldn't afford much. But yes, I believe her son did all plugs as stated, the wires are new. I was there when we bought it, the truck ran great. The previous owner said it sat for months with an external coolant leak, he thought it was the radiator and just tried to sell it instead of fix it. After we bought it, I found the leak and had to replace the t-stat housing as it had the infamous crack at the bottom. So yes, I did spend some time with it 6 months ago and it ran great.

I haven't done anything myself with it since we bought it. Her son did some additional stuff like door handles and other stuff, but as far as I know it has ran fine until last weekend. I'm not sure a fuel injector is at fault. With the gas smell and bubbles, I plan to do a compression check tomorrow. It was low on coolant today after I filled it up last Monday, not as good sign. Just wanted some opinions on this and the possible SOHC head gasket replacement.

 

[2000StreetRod]

replacing head gasket

I'm surprised that you still thought it was the OHV V6 after replacing the thermostat housing. Anyway, replacing the head gasket ($45) requires replacing the intake manifold gaskets ($20), exhaust manifold gasket ($10) and retiming the camshafts - a fairly involved process that normally requires a special timing tool kit ($150 to $200 used). Also, Ford recommends replacing the head bolts ($30 to $40) although at least some members have reused them.

I suggest that you make certain the head gasket is blown before proceeding. The coolant could have been low enough that there were air bubbles in the cooling system and you saw them escaping thru the coolant reservoir. Also, the head could be cracked. A compression test is definitely needed.

 

[koda2000]

i would not recommend reusing the head bolts as they are torque-to-yield. for me it's not worth the risk of undoing all the work of replacing the head gasket for a set of $30 bolts.

 

[my98nnj]

Your local mechanic should have an analyzer to tell if if exhaust gasses are present in the cooling system. Figure about a $50 diagnostic charge, unless he's a member if your church...