Haven't posted here in a long time, my truck hasn't had that many problems lately.

Anyways, I've had this gurgling/rushing water sound coming from the heater core area of my truck for a while now. Lately it's gotten pretty bad, and I read that it can be caused by low coolant level. Checked this evening and found the reservoir empty, but the bottom was coated with what almost looked like brown mud. Under the radiator cap, the coolant was up to the top of the radiator where I would expect it to be. Color was pretty brownish and there was more of this "mud" on the cap and surrounding area. What are the most likely culprits here? Is there oil getting in the coolant from a gasket gone wrong somewhere? Rust from the block? The coolant isn't very old, less than 5K (had the water pump replaced then. I was out of town with no tools and had to have a shop do it, which I never do) The engine consumes about as much oil as I would expect a 17 year old truck to: just a little bit. Also, the truck runs very cool, always has. Even on a hot day with a load in traffic, the temp gauge never goes past the "T" in temperature. Drove ~160 miles a few days ago, temperature gauge barely budged.

Truck is a 1994 F-250 4x4 E40D 7.5L, with about 145K on it.

 

lol just cause the gauge didn't move much, may just mean its not working. I would suspect oil getting into the coolant somewhere.

 

when the water pump was replaced, was the system flushed?

 

Yes it was, or at least that's what the shop told me.... Coolant looked pretty fresh afterwards.

 

i did that too with mine it was a new thermostat, put new coolant and everything in. started overheating on me so i thought the thermostat was faulty, when i went to drain the rad to drain coolant nothing came out....the radiator was plugged up and full of brown cukka, ended up putting new rad in, and i busted off the side tanks to investigate...sure enough about 4 rows plugged up solid