Oil in coolant

I have an 88 k1500 w/ 4.3 v6 and manual transmission.

I was flushing radiator and after a few drain/fills it seemed the water was just as dirty. Looked oiley so I thought blown head gasket. Checked the oil and it was low but it was just oil. Searching online I found someone who replaced the radiator and fixed the problem.

My radiator is also an oil cooler so if coolant pressure is 15 and oil pressure is 30 I guess that would make a one way flow. Is there any way to check this out without just buying a new radiator?

Engine coolant can appear oily due to a leaking transmission fluid cooler or by sludged up Dex Cool engine coolant. Check the trans fluid and make sure that is clean.

The logic about the pressure differential is not correct. If you assumed there was a breach between the cooling system and an oil pressure galley oil would flow into the cooling system at those pressures. However, when the engine is turned off and the oil pressure drops to zero the cooling system will still have pressure on it so coolant would weep into the engine oil.

It could be that a badly clogged radiator could be causing this. In some cases vatting them out at a radiator shop will clear them up but the cost of this should be compared to a new radiator before having the old one vatted.

I don’t think a manual trasmission has a cooler.
If there is just a pinhole in the oil cooler, wouldn’t it cool down before more than a trace amount of radiator fluid could leak into the oil? Lets say 5 min cooldown vs 60 min runtime. My eyes just aren’t good enough to catch just a little mix. I’ll have to look a little closer. I had a Safari that blew a gasket and not only could I see there was a mix in the oil but the dipstick read over not under.
More info. When I flushed the radiator without running the engine water came out clear. No, this isn’t a test. I just forgot to mention it before.

if you have a cooling system pressure tester, you could remove oil lines from radiator and put the cooling system under pressure and watch for coolant to come out of oil cooler fittings. Even if you have just a pinhole, coolant is thinner than oil.

guess I’ll have to see if autozone, advance or o’reily has a pressure tester to lend

Yes, my bad. I had forgotten this was a manual transmission while thinking about the problem.

Parts stores like you mention do have a cooling system pressure tester that you can rent. Once you return the tester they will refund all of your money.
I do not know what any paperwork with the tester will state but the paper with mine says to allow 5 minutes to detect any leakdown.
In my opinion, this is not long enough and I always allow at least 10-15 minutes. It’s also not a bad idea to apply a small dab of heavy grease to the tester where it attaches to the radiator. This can help to seal off an aged or distorted gasket on the tester which could possibly lead to a reading leading you to believe the cooling system has a leak when it actuality it’s only the attachment point of the tester.