Hi everybody, been finding great info on this site for the past few months but this is the first time I've had to post for some help. Sorry for the long initial post (i'm a prior flight engineer so I'm used to writing long write up's for mechanics lol) but I'm sure there's some of you that can give some advice before I tear this engine open, which I rather not do.
Bought a 96 f150 4.9l with 136k a few months ago since I'm moving to Wyoming in may and wanted a 4x4 truck to get around. Spent the last few months giving her a good tune up and fixing her up. Here's my current problem through, tried searching but couldn't find anything exactly relating to my situation....
a few days ago I flushed and replaced the coolant as one of the last things I had wanted to do before I figured she was good to go. Well, drove her for about a hour to the beach and back and she ran fine, no smoke, no cooling problems, everything seemed normal. Went back to the check the coolant the next day while it was cold and noticed a few things.
For one when I opened the radiator cap I noticed brown spots floating in the green coolant, and what seemed like brown sludge on the bottom of the radiator cap. At first i was thinking this might have been left over crap from when I flushed the radiator, but upon looking closer it seems pretty much like oil to me. Then checked the coolant reservoir and it had the same brown spots as well as being about 1/2 full according to the cold fill line. It had been filled right up to the line before I drove it. Checked the oil and it seemed fine but was higher from when last time I checked it.
I consider myself a pretty experienced shade tree mechanic, so I feel all this is pointing to a bad head gasket. There's a few things that are making me hesitate to think this the case through...
For one the fact that their's no smoke coming out the tail pipe seems weird, all the other bad headgaskets I've seen have had some kind of smoke, either white or blueish come out the tailpipe. Might be just a small leak not enough to smoke?
Second when I flushed the radiator I musta ran it with water about almost 10 times till it started coming out clean, and on my last try ran it for a good 30 minutes and got it nice and warm. When I emptied it out the water was nice and clear, no oil or anything. Thinking the longer hour drive might have something to do with this?
Lastly I would expect to find something when checking the dip stick, bubbles or milky oil or something. Except for it being higher than normal through it seemed fine, maybe alittle lighter in color than normal, but that just may be in my mind since I'm paranoid now about this problem. Had a friend tell me i should try to put a lighter under the dipstick and see what happens to the oil. If it bubbles or anything it would show that water was in it according to him. Seemed to make sense so i tried it. No bubbling or anything, eventually the oil caught fire but nothing that would make me think there was water mixed with the water.
I did get 2 trouble codes, p0135 and 133, which are o2 sensor codes, but I do not think these are related to this problem. The idle was slightly lumpy while at stop lights through, but other than that no problems, engine oil and coolant temp was perfect, engine ran fine, everything seemed fine.
My conclusion? Either I have.....
A.some kind of head gasket problem, causing coolant to leak into the oil (hence the higher oil level, lower coolant level, and spots in coolant)
B. something else leaking cause the same problem
C. brown spots are just left over coolant crap from the flush
D. something else I haven't thought up yet
I plan on do a compression test and flushing the coolant a few more times to make sure I got all the crap out, then take it from there. Any thoughts or ideas on what else i could check before i tear it apart? (after that long post if your still awake lol)
Along with a headgasket, I would like to know if the coolant smells like gas, or smells like oil as well. The odd chance is it could be a cracked head but that would make your coolant overflow tank start increasing in level as well as pop the cap. Just to be sure, I would flush the cooling system one more time to rule out anymore crap, or flushing agent, if used. If the problem persists, then I would be removing the heads, and start tearing it down.
may sound odd but try a new cap, sometimes the rubber gets "gunky" on them. can you take your finger and wipe the cap where the rubber comes off? still check the other stuff but new cap is cheaper and less consuming than the other stuff. sorry if it sounds ridiculous but had it happen.