CaptKirk

I have a 1999 5.4L, 2-valve, 4WD, automatic with approx 135,000 miles that I inherited two years ago so I've never worked on this engine before. I only put about 500 miles on the truck per year because it is parked at a farm about 30 miles away that I also inherited.

It recently and suddenly developed a pretty bad internal coolant leak. The only symptoms right now are considerable coolant loss from the radiator reservoir and LOTS of smoke/water-vapor out the exhaust when I crank it cold and of course a skip/mis-fire until all the coolant is purged by pressure and heat. There is no hard evidence of coolant in the oil and no oil in the coolant reservoir as of now. No leaks anywhere on or under the engine nor in the valley between the heads. I suspect bad head gasket but have just started diagnosing the issue. (NOTE: The truck has probably only been driven 30-50 miles since the smoke/vapor started pouring out the exhaust.)

I've been reading a lot here but need two specific question answered (and probably others later). (1) Does any coolant actually flow THROUGH the intake manifold. (2) How do I keep the ignition from firing when I start turning the engine over to check for compression leaks after pulling the COPs and plugs. (Probably not good to let it continue firing during that time.)

Thanks for your help.

99F150V6

Yes
Remove the fuel pump relay to disable the fuel pump or remove fuse 18 (15Amps) from the battery junction box to disable the injectors

CaptKirk

So it appears that if my coolant leak is because of a failed intake gasket it would normally show coolant externally at one of those four corners of the engine, in the valley between the heads, or in cylinders #1,4,5, or 8 - right?

By the way, the truck is 100% original, no mods of any kind except replacement of standard wear parts (brakes, starter, etc.)

Thanks.

CaptKirk

Great pic! Thanks.

Snake plissken

Is your INTAKE plastic or aluminum? My 1997 is aluminum my 2000 WAS plastic but I found a good aluminum for it with no problems. Aluminum intakes are much better and use gaskets where the plastic ones used seals. Plastic is much more likely to leak or crack.
I would think if it's leaking you would see coolant in the valley but you said you saw nothing.
Could be a head gasket.

CaptKirk

Best I can tell it is aluminum. I can scratch it with a pointed object/screwdriver and see what looks to be shinny aluminum. Is that sufficient proof?

Yes, I also think it is head gasket but don't want to overlook what is apparently a high failure item as I evaluate.

CaptKirk

New-Additional info from the OP:

After sitting overnight the truck cranked right up with no smoke & no skip for the first 1-2 minutes while idling. It then began to put out 1 puff of smoke on probably every revolution. As I sped the engine up the smoking/water vapor got MUCH worse quickly as well as the skip. I held it at about 2000-2500 RPM (no tach) for 30-45 seconds and the engine began to die and then choked down and would not re-start.

I still suspect bad head gasket and maybe leaking between 2 cylinders. I'm guessing that as the RPMs increase you're pulling more coolant into the cylinder(s) more rapidly causing more smoke and then no longer able to run with maybe 2 plugs wet. I suspect it will crank fine after sitting for a couple of hours or over night

Is it OK to pull the connector from one COP at a time with the engine running to try to determine which plug(s) are not firing. Will it hurt the COP or any part of the ignition?

mbb

Not exactly true.

The factory for manifolds use gaskets. Only the el cheapo dorman/ chinese offbrand replacement uses some seals.

Since the composite intakes last 15 plus years..... Any replacement motorcraft intake will outlast the vehicle .
The composite may also be higher performance because the runners are smoother. Unless you want to go and have your aluminum one ported, polished, and flow matched ..which would be The only good reason to go out of your way to find an aluminum one .imo.
.
As to the op..... If your head gasket leaks into cyls while it's running..... It's probably a big enough leak to show up on a compression test....... If nothing shows on a compression test do a leak down test on suspect cylinder holding it at TDC ... With the cap off the reservoir
.... When your reservoir overflows you'll have your answer

You can also do a block test on your coolant. Lack of color change on a block test is not a negative confirmation... It can leak only from the coolant system into the cylinder and not vice versa. . But a positive color change is a positive confirmation.

Snake plissken

Composite is better than plastic and of course I have not seen EVERY year vehicle intake....just mine. My 2000 came with a plastic with seals but I bought it used.
I hate plastic.
Is every new vehicle intake manifold composite?? If so they are probably ok.
Big difference between composite and plastic.
I'll take ALUMINUM over composite or plastic any day. I can weld aluminum and machine it true. I would not trust the other choices if they fail.