I just bought the truck a few days ago. On the inspection it had a few little blobs of stuff floating on the coolant so I new something was wrong. After a few hours of running it there's now a thin solid layer floating, but I can't tell for sure if it's oil or fuel. Any definitive way to know? I thought about adding leak detection dye to the fuel or oil but not sure if that could hurt anything. Thoughts?

 

Does it smell like diesel? Can you get a sample of the of just the stuff floating on top?

 

How dark is it?

You can dip the end of a shop rag in there and see what it smells like (besides coolant).

 

More than likely fuel from the injector cup seals because when it is oil from the oil cooler is almost surely going to be very black against the coolant color. Pull the dip stick and see if the oil color matches the stuff in your degas bottle, if not probably fuel. And as said if it is fuel you should be able to smell it.

 

It smells like it could be diesel, but not definitively diesel. It's dark, but I don't know if diesel would pick up darkness from the hoses. I've tried smelling it hot and cold, straight from the bottle and off a napkin and it just smells like a petroleum product, along with the coolant smell, but can't tell from the smell if it's diesel or oil. I think diesel smell would stand out, but this truck sat quite a while so the diesel isn't gonna smell quite the same as fresh stuff.

I guess I can make a couple jars with coolant and add some diesel and some waste oil and see how they act & smell to hopefully narrow it down.

 

If your injectors o-rings are worn you can get oil in the fuel too (which may then be going into the coolant). You can open your fuel bowl and look at the filter. If it's black (the filter element is white) then you have oil in your fuel. If that's the case you might see increased use of oil and your mpg might go up some too. That's something that happened to me.

The injector cup and o-rings separate oil, coolant, and fuel in our HEUI system. Things will go the path of least resistance (and lower pressure) so everything flows "downhill" to the coolant since the oil is 500-3000 psi, fuel is ~60 psi, and the coolant is ~16 psi.

It's difficult enough to figure out what is "leaking" and even harder to figure out where, especially if you want to narrow it down to the failure point instead of a blanket repair (e.g. replacing all injector o-rings instead of just the one that failed).

 

And because you haven't mentioned what your mileage is, My Money says your injector rings are done.....And because the Golden rule dictates that you don't want to do the injector work 8 times.......One time in and done

 

Depending on the amount, get a turkey baster or a mighty vac and suck the stuff out of the reservoir. Keep doing that and adding it to a jar. When the jar is full enough, put a little hole in the bottom of it, or flip it upside down and crack the lid just a hair and drain the coolant out since the diesel / oil will be floating on top.

Then look at what's left and determine which it is. Diesel is my guess. You can also pull the oil drain plug on a cold engine that's been sitting a while. If it's an oil cooler leak, you'll have water in the oil which will come out first in that situation, plus you'll have the chocolate shake look on your oil dipstick while hot.

 

Seems very odd you'd come to that assumption. It has 425k miles, but the miles mean nothing. I just bought it a few days ago and have no maintenance history. The cups could be near new or original. There's no oil in the fuel, I checked that right away.

 

Brilliant! I'll start doing that. I'm also going to look into making a pre-separator. A small catch inline with the coolant tank to hopefully contain the floating stuff in something where the top is fully accessible. The tank has so much inaccessible area.

 

I assume that because at 400K , I don't need Tea leaves to bet that your Injector O-rings or cups are shot or close to it. Oil floating in your De-gas bottle is a Very good indicator. and I can predict that cause it's happened to more than a few of us. Your truck has a whole bunch of O-rings in it and they usually need some sort of attention around 150K so......Floating Diesel tends to look like Oil drops rolling around inside the tank, and it's green, so it blends in with the Antifreeze. The variant to that opinion is it could be the Oil Cooler might be leaking between the tubes. It's the only other place the water and oil come together...

 

But if they were recently replaced by a precious owner then they should be fine, hence my saying that the mileage means nothing.

My floaters are pretty dark. But diesel breaks down hoses so I assume it's possible that the darkness is from the hoses. I assume the cooler is easier to reseal than replacing cups, but I don't want to do both if it's not needed.

 

You've got me confused.

 

You hadn't mentioned that before, but the song remains the same.....there are only a few ways for oil to get into the coolant. And the PO may have said he replaced the O-rings and such, but you only need 1 to be pinched, cut or dried out to let the Oil in...Not ******* you, just staring into my crystal Ball. Or it might be a Nightmare I've had come back to haunt Me......who knows

 

The PO said nothing about having replaced anything but the alternator, oil, and I think the belt tensioner. He rarely drove it, it mostly sat around. According to him it wouldn't cold start without ether, apparently he didn't know about glow plugs because it has cold started fine for me. It appears to not have been damaged by the ether, no smoke or odd blow-by at least. I have no service history on it beyond what the PO stated.