Oil in overflow tank

have a 96 5.7 160k , noticed about a 1/2 in of oil floating on top of the coolant in the resivior tank.I replaced the radiator last august when the trans cooler side failed and puked into the res,(along with taking out the tranny that dexcools some nasty stuff) now its engine oil in there, where else besides the cooler tubes in a year old radiator could this much oil be injected into the coolant? Oil dipstick is clean but i havn't pulled the base plug to see if theres coolant under the oil.

have a 96 5.7 160k , noticed about a 1/2 in of oil floating on top of the coolant in the resivior tank.I replaced the radiator last august when the trans cooler side failed and puked into the res,(along with taking out the tranny that dexcools some nasty stuff) now its engine oil in there, where else besides the cooler tubes in a year old radiator could this much oil be injected into the coolant? Oil dipstick is clean but i havn't pulled the base plug to see if theres coolant under the oil.

oil floats....pressure test coolant system..check cylinders for coolant when pressure testing...[remove all plugs]

the problem could be the head gasket could be worn out

thanks shawcross, I wasn't thinking that the head gasket had any pressurized oil passages that could let oil into the cooling system i could be mistaken, is there?

Today I found out that oil floats on water, thanks jcat

I guess by your remarks we are speaking about eng oil not tranny fluid. The eng oil does have more pressure then coolent as you know your coolent cap is rated apx 15 lbs I believe, and hopefully you have 35-50 lbs or more oil pressure. I dont know off hand the oil flow thru your 350 but I would think intake could or head gasket could allow oil into coolent if now one here answers this my neighb rebulids engs has mach shop I will ask him monday for you if you need. let me know

thanks ron, it pretty easy to think of all the ways water can get into the oil such as an intake leaking into the lifter valley but the other way arround has me asking. As i stated earlier it would seem that to overcome the pressure in the cooling system the oil has to be coming from somewhere that has pressure. maybe i just need to pull the rad and have it tested and go from there,mine has the optional oil cooler in it and thats the obvious place to start even tho its only a year old.

where is a oil sendin unit located on a 1990 chevy suburban???????:banghead::runaround:

I tend to agree having a oil cooler sys it would seem that would be most logical place the two liquids cross path with pressure. you may be able to put pressure on those oil lines with rad cap off rad to check while still in veh. But those lines and trans lines are the pains in a anyway and once off really not much more to take completly out to check. As I said my friend does rebuild engs so if this doesn't work out just let me know. do privite message because I may miss checking posts. But I think you may just have it let us know.Oh P/S my other friend has junk yard he just got me new rad for my wifes 97 blazer(plastic crap) he told me those vehs have head gaskets blow because of that dexcool fluid needless to say I replaced coolent with normal green coolent just food for thought. Good luck

where is a oil sendin unit located on a 1990 chevy suburban???????:banghead::runaround:

My '88 5.7 liter Suburban had two, and the factory '88 GM repair manual was wrong about this detail. Apparently the one detailed in the repair manual was near the distributor base, and that one actuated the idiot light (book stated for oil pressure gauge). However, the oil pressure sender for the gauge is actually located underneath, just above the oil filter. It was the second sender that was bad on mine.