oil pressure drop and oil in coolant

[63A]

I'm trying to help a friend get his Ranger going again. He recently replaced the long block with a rebuilt LB from a local engine shop. After the swap, he said it was running fine for the first 100 or so miles, but while driving around town, he noticed the oil pressure fluctuating and then dropped to zero. He stopped and had it towed home. Other than drop in oil pressure, engine seemed to be running fine up to that point. Once home home, he looked in the radiator and noticed oil in the coolant. He is thinking head gasket which makes sense with the oil in the coolant but I'm wondering if there is another underlying problem that caused the oil pressure problems which caused the head gasket to fail.

I'm going to help him replace the head gasket but am concerned that may not fix the oil pressure problem.

Anybody have a similar experience. Replacing the head gasket won't be too hard (I hope) but would like to understand what happened.

Thanks

 

[RonD]

If it has automatic trans then oil could be trans cooler leak.

And with head gasket leak only between cooling passages and oil passages(not very common) you would expect coolant in the oil as well, and you didn't mention that.
Especially if oil pressure dropped to 0psi.

Low or 0psi oil pressure will usually cause valve train noise, was that happening?

Ford uses an oil pressure switch as the sender, when under 6psi of pressure the switch is open and oil pressure gauge reads 0psi, above 6psi the switch closes and oil pressure gauge reads about 1/2 way, so on/off gauge no in between.

disconnect coils, remove sender and crank engine, see if oil pump out of the hole, or if possible install a temporary real oil pressure gauge and see what the actual pressure is when engine is running.

 

[63A]

Thanks Ron. I'll ask about coolant in the oil- hope he didn't drain the oil so I can see what it looks like. Will also ask about valve train noise when he noticed the oil pressure fluctuation.

I didn't know that about the oil sender. Based on your explanation, it would make sense that low oil pressure (like could be caused by oil diluted by coolant) could cause significant fluctuation on the gauge.

The truck is a 5 spd so no trans cooler leak.

 

[tomw]

If antifreeze got into the oil sump, it will form a goo when mixed with the oil. The goo could be plugging the oil pump pickup. If goo is not formed, and there was water in the sump, the oil would float on the water, and possibly allow the pump to pickup water as the lube. That is not good, and will result in damage.
If the only symptom was the gauge dropping to zero, and there was no cam follower clatter, then I'd suspect the sender wire may have come off, or similar. I would get a low budget gauge kit with mechanical oil pressure gauge, and install the gauge underhood to see the actual pressure developed. If satisfactory, then trouble shoot the gauge problem. If the pressure is low or zero, check the oil pump drive shaft & hex in the bottom of the distributor. If there is no distributor, there is something else that drives the pump from the aux shaft. I didn't keep up with all the differences. You might have a dummy distributor shaft & gear that drives the pump. Either way, check that it is being driven.
The oil could have been from the old engine if it had a gasket failure, and is being driven from the radiator by heat and coolant flow.
tom