Losing coolant & oil, MPG down

[south59]

A little background: I got this truck at the beginning of this year with 122,000 miles and shortly thereafter switched over to synthetics. It had been a good 2-3 weeks since I had checked the fluids, so yesterday I decided to see how everything looked under the hood. I found a few things that alarmed me...and wanted some suggestions on what the problem(s) could be. Its a 99 v8 btw.


1. Oil level was down below the dipstick mark(no oil on the stick at all), i had to add 1 and a half quarts to get it back up to normal I used the excess Mobil 1 10w30 that I had from the previous oil change. (Under hood wants 5w30)

2. Coolant overfill tank was just about dry...Lots of black sediment on the walls of the tank...The radiator was full however...Looked to be bright green. I filled the tank up about halfway since I have to drive about 150 miles tommorow. In the past I had noticed that the overfill tank was a dark greenish hue when it actually had coolant in it.


The truck is driving well, no noticable lost of power...But i have noticed that my gas mileage has gone down in the past few weeks.

What in the world is goin on? When It comes to diagnosing something like this im completely clueless....I know the head gaskets on the v8's are pretty damn durable... what about the seals?

What would explain a simultaneous coolant and oil loss?

Thanks

 

[Turdle]

Sounds like a blown head gasket, possibly an intake manifold gasket.
maybe a cracked head.
I would start by reading the spark plugs, but that's me.

 

[je5]

The lower gas mileage could be from the low fluid levels. The coolant "could" be low because the oil level was low causing a moderate amount of overheating. The oil level "could" be low because you switched to synthetic on a high mileage engine. Check levels weekly and see which is causing the problem.

 

[aldive]

Have you performed a compression test?

Is there any coolant in the oil?

Leaks on the ground?

 

[south59]

Havent done a compression test aldive, and there are no external leaks while the engine is on or off.

I might go pick up a compression tester tommorow before my trip to see whats going on, which will also give me a chance to check out the plugs for contamination.

hows the labor for a head gasket or cracked head?

 

[south59]

Dont know if this is related at all, but I have noticed that when accelerating hard, the AC completely stops blowing and resumes when i let off the gas.

 

[aldive]

Th AC compressor should shut down under WOT conditions; I don't know about the blower????

 

[south59]

Th AC compressor should shut down under WOT conditions; I don't know about the blower????

I guess I phrased it wrong...this happens under normal accelerating conditions....For example, entering the freeway or going up a large ascent where your pushin it a little more than normal.

Looks like its unrelated anyhow, probably a vacuum leak in the AC system..