Coolant leak...:(
 

OK...since I have had the truck I have noticed a slight smell of anti freeze...two years or so. Truck never overheated. I did have it flushed before as the antifreeze looked like mud. I never have been able to keep coolant in the overflow container. I put some coolant in the overflow up to the line a week or so ago and the coolant smell got stronger. I got home one day and when I came back out I had a puddle of coolant under my truck...center of the vehicle behind the wheel axle area in the front. I climbed under and couldn't see where it was coming from...looked at where the overflow line from the overflow container went and it appeared to be from there....but I really am not sure of that. Last night I ran the truck to the bank and let it run while I was at the ATM and when I got in the temp needle was above the half way mark...started to drive and it went back down. I did put some coolant back in today...about quart and a half directly into the radiator and then put some in the overflow tank to bring it up to level. I DO notice what appears to be a leak to the right of the water pump under the AC compressor...looks like a intake leak. I did check my oil...clean. I DO have gunk on my radiator cap though....photo attached. I also have an intermittent issue where the truck shutters...I thought it might be OD going out at first, but the last time it happened my SES light started blinking...that might be a separate issue though as when I looked at the spark plugs they were Autolite and I know I haven't changed them since I bought the truck around 90000 miles...its at 138000 now.

One thing to check is the water pump. They usually have a "weep Hole" at the bottom to allow coolant to get out when the seals inside the pump begin to fail. Just a thought.

Yeah I'd say start at the waterpump. that's what it sounds like... Mine literally just went out like 2 weeks ago. Pretty easy and cheap fix.

And do a complete flush, get all that crap out of the tank!
I switched to the green stuff and haven't had any problems. The Dex-cool clogged up the coolant recovery tank, heater core, water pump, and all the hoses...But if the bottom side of your cap looks that bad, you really need to clean out your entire system...

also that rad cap may not have been keeping enough pressure in the system

It looks like a previous owner may have put a "stop leak" in the system. That is the brown "gunk" you are talking about. By flushing the system, you removed some of it and got the leak back.

Green stuff FTW!

Well....1100 dollars later and the truck is back up and running. I had my mechanic come by and he pressurized the coolant system....started spraying from the front and back of the intake manifold. I watched him take it apart and when he pulled it off you could see where it had failed BIG TIME in each corner, one in front, one in back. Initial costs were around 630 with labor...that included replacing two motor mounts. Once he got it off though he was like...."the cap, rotor, plug wires and spider are ORIGINAL and if your going to keep this truck...I HIGHLY recommend you replace them now...or I'll be back later" So...I went ahead and replaced the cap, rotor, plugs, plug wires, spider and thermostat...the spider is EXPENSIVEeee...but went with all AC Delco except the thermostat.

He did shake his head when he came in to let me know it was done...said the spark plugs...were all goofed up. On one side someone changed the plugs to platinums, but on the other side they were non-platinum. THE SHAKING HEAD PART....plug 3...was the ORIGINAL PLUG!!!! He said the core was eaten totally away! My truck has around 138000 miles on it...it's a wonder it was running. Just before this all went down though I did have two instances about a week apart when going up a hill, the SES light would blink..and I BET...that was the reason...