I've got oil in my radiator but not the reverse in either my oil or my transmission. What would be the cause of that?

Question

I've got a 97' GMC Yukon that I'm looking at. I had to get into the upper intake manifold to troubleshoot a fuel issue so I had to drain the radiator while getting access to it so not to make a mess. I was not paying attention to what was actually coming out until i refilled the radiator and looked inside and found globs of oil mixed in the radiator. I checked the dip stick (the oil had been recently changed) and i found no milky white substance to indicate immediately a head gasket issue. I've got lines going from my radiator to my transmission so I checked the dipstick and i found that the transmission fluid had been overfilled but still red and smells sweet and no indication of water. I wonder if i caught something early enough to prevent something serious.... but im scratching my head where to go at this point. Someone said that maybe the previous owner had put oil in the reservoir by mistake. I dont think this radiator has been flushed before. What are your thoughts?

Answer 1

You have a bad head gasket that is allowing oil to leak under pressure into the coolant. Time to replace a head gasket and if you can't do it yourself then you are looking at $1,000 - $2,000. In some vehicles this can be caused by some other gasket rather than a head gasket, but in any case it's going to cost some money.



As time goes on, the oil will accumulate more and more in the radiator until it starts to plug up the tubes and your engine will gradually start to overheat more and more. So if you see this happening then you will have to flush out the radiator and get all of that oil out. The leak will get worse over time and you will have to do that messy job of flushing the radiator more often. Adding some laundry soap (which doesn't suds up) to the radiator will extend the time between flushings buy thinning out the oil.



Edit:

If you have gobs of oil in the radiator, and if the transmission fluid is overfull, and if you think it's a trans cooler leak, then that means gobs of trans fluid left the transmission and was replaced by gobs of coolant plus more coolant to over fill the transmission. And this most likely didn't happen overnight, it was a small leak that got larger over time. Yet the trans fluid looks OK and the transmission shifts just fine! And it had all of that coolant in there and probably has been for some time. Sorry, but that seems unlikely. It's most likely a head gasket leak which has more pressure than the coolant so it is a one way leak only. But like I said, it could be some other gasket in the engine rather than a head gasket.

Answer 2

The ATF cooler may be leaking inside the radiator where it's mounted. If that's the problem just replace the radiator.

Answer 3

Sweet smell is antifreeze. Rad has cooler in it. And is mixing antifreeze and transmission fluid. Don't drive until checked and fixed . Antifreeze in an automatic transmission will kill it in short order..............You have antifreeze in radiator just not enough to see yet. but you can smell it. You need to have radiator fixed and trans flushed. This may...save it but not a given.