My 1989 bronco with 300, 5 speed, 163k started pushing oil into the cooling system about six months ago. About a quart every 50 miles give or take. I've watched it very close and it has yet to get coolant into the oil. The oil on the dipstick goes down, the level in the coolant overflow goes up and will actually overflow if I don't drain it down. This engine runs excellent otherwise, good power, no smoke and it has never been hot. I am the original owner. It is a manual trans with no oil coolers whatsoever. Can anyone tell me the possible places that oil and coolant can get together on this engine? Would the head gasket be worth replacing? I can't understand why the coolant does not go into the oil unless my radiator is not holding much pressure. The temperature runs the same place it always has. I changed the water pump, thermostat and thermostat housing a few months before this problem appeared and was wondering if there is any way for oil to come in through possibly a bolt hole that goes all the way through or something. I've taken it to several reputable mechanics in my area and no one has been able to diagnose the problem so I have been reluctant to let anyone just start tearing into it. Thanks for any help

 

At face value, sure sounds like a blown head gasket or (let's not make it worse). Some oil (oily residue) in the water is a sign of a blown head gasket because the pressure in the cylinder is great enough to force gases into the water jacket, but not a quart of oil. You can usually see an oily film/line in your radiator overflow/recovery tank. So if you compression checked each cylinder and they all held their pressure, then maybe something is happening where the water pump bolts on the motor.

 

The compression checks out on all cylinders and the plugs also look good. I can't detect any bubbling in the radiator either so I am reluctant to think I have head gasket trouble but I'm just about ready to check it anyway just from the lack of any other ideas. I may go ahead and pull the thermostat housing and water pump this weekend to take a look see behind them. I was hoping though that someone on the board might have already been down this road before since these engines have been around for so long. I don't have any flow diagrams of the oil or coolant but I will probably try to get some since I believe they would be very useful. Thanks again for any help.

 

I had an 82 with a 4.9 that did the same thing. The block was made by what is called sand casting. Unfortunatly,there are weak areas in the block between an oil and a water passage that will wear through allowing the condition such as you have. I hope this helps and I hope it is not your problem. The only fix is a new block.