I had a similar leak. I ended up spraying down the whole underside with brake cleaner to clean it up real good. Then I idled it in my driveway for about about 30 minutes. Mine turned out to be a really bad power steering pump leak.

 

@Richard Gallant I think you are spot on with the rear valve cover....The outside corner looks good, but I can't see the inside corner but I can see where the oil is coming somewhere from that area. Going to have to pull back down to there and figure it out.

At the moment, we have a bigger problem that has me baffled. The engine keeps over heating due to getting air in the cooling system. From cold, if we bleed the system then all seems to be well, but after a few trips, somehow air gets back into the lines and it will overheat again. We have lost coolant due to bleeding, but I don't think there has been any loss due to a leak. This whole process started with overheating problems, but before the head gasket replacement we could see coolant leaking from multiple points around the block. I'm not seeing any sign of any leaks at this point. When it does overheat, the level on the coolant reservoir will be higher than it was when we started from cold. One more thing to mention is that the throttle body heater had been bypassed. However, since the head gasket kit came with the throttle body heater gasket/replacement, we decided to put it back in place. Not seeing any leaking with any of that and pretty sure we put it back together properly although the original hard line was missing so I just replaced it with a hose for now. Any thoughts on what to check? This has been terribly frustrating because we can't seem to figure it out. Vehicle runs fine for 15 mins and then suddenly the temp jumps. Keeping a very close eye on it, but I realize not catching the heat jump soon enough can lead into MUCH bigger problems. Yesterday, from cold, we bled the lines before starting the vehicle (and there was a good bit of air in it) and then drove 40+ mins with no problems at all. Seems like air is getting in after or while it cools off? If air can get in why wouldn't fluid be coming out (leak) when it does get hot? Sorry for the rambling, just want to give as much info as I can.

 

I had a bear of a time with the valve cover gaskets, spent an hour on the passenger side and about a half on the driver's. You have to work very slowly while tightening down the 4 bolts and make sure that the gaskets stays perfectly uniform around the perimeter as you go. Any bulges or deformities means it's no longer properly seated in its groove.

At this point I would think that you've gotten pretty good at bleeding the system. Have you followed all the procedures to fill at the T, make sure the heat is on, ETC? You may want to get a cooling system pressure tester and see what the results are. Compression and/or leak down for the engine too for that matter. Pressurize the cooling system to about 10PSI and see if it holds, and for what length of time. I placed cardboard under the truck so any drips would be easier to trace back. I would caution against going higher than 10, I made a minor leak where the head meets the block in the area behind power steering pump much worse by repeatedly pressurizing to 20 PSI. How's the cap on your overflow bottle? That needs to seal well too. When you said that yesterday you bled it before driving and found "a good bit of air in it", that makes me nervous, it has to be coming from somewhere. Compression and leakdown will tell you if there's a problem sealing the combustion chambers, and maybe get the kit which tests for the presence of hydrocarbons in your coolant just to be safe. Have you checked the radiator for proper flow? Those are all the things which come to mind at the moment.

 

@ahab Followed your suggestion and went back for the coolant pressure check. I did this before started the project and found that it held pressure fine while the engine was cold. However, I pressurized to 10psi as recommended and after about an hour, it had leaked down a couple psi. but still not seeing any sign of a leak. I went ahead and pressurized to 15psi (no more) and kept a watch. I'm still not seeing anything. However........I can hear what sounds like a drip coming from inside the engine like maybe dripping into the sump? One drop about every 6 seconds or so.

 

Well, from what you describe I would drain the oil and look for water. If it's not appearing on the outside anywhere then perhaps it's an internal sealing problem. A couple PSI in an hour is not a good sign. We're getting outside of my experience and talking theoretical at this point, but the only way you'd have a leak dripping into the sump if it's not a headgasket problem is a cracked block. That's pretty extreme and from what I know that's more of a freeze scenario than an overheat, but this is my first aluminum engine. I'm not trying to be a wet blanket, there are lots of things to test, but after a couple thorough bleedings and consistently pressurizing the cooling system to the point of overflow you have to start look at worst case. If nothing else to rule stuff out. Because of the sleeves I don't think a compression test would identify a cracked block, and a hydrocarbon test wouldn't either, coolant in the oil would be a smoking gun however. That would be my next move. HTH.

 

I left the system pressurized overnight and it only dropped from 15 to 12 after 8 hours or so. I was hopeful for a minute when I found a pin hole in the small hose coming off the top of the radiator, but not enough to account for the pressure drop. I drained the oil and wasn't sure what I was looking for and initially felt relief as there was no visible water "on" the oil. However, the oil was a lot darker than I expected after only a couple hundred miles tops and had a coffee/chocolate color to it. After a bit of research, I'm pretty sure that is not a good thing. I heated up a coke can on the stove to about 350-400 and placed a few drops of oil in it and while it didn't bubble significantly, I could see small air bubbles forming in the oil which was one way mentioned to check for antifreeze in the oil. I also pulled the plugs on the corners of the block and inspected the cylinder with a camera. They all looked clean. I would love for someone to tell me I am misreading this.

 

wipe a finger tip inside the oil fill cap and taste it. If its bitter sweet, it indicates antiF in your crank case. And chocolate color is a bad sign of AF in your oil as well.....

 

Desperate, I decided to give blue devil a try as a last resort. Unfortunately, no difference. Idles fine, but then after about 15 mins of driving, it overheated again and you could hear air in the cooling system yet again. It overheated pretty near where I got it from, so I parked it there and will give my buddy a call Monday and figure out where to go from here. At this point, there was something sadly satisfying about not bringing it back home to sit in the driveway. Still thinking on it and open to ideas, but have spent a lot more time than intended and still don't have a driveable vehicle.

 

I would drop the oil pan and pressurize the system. Then lay under the truck and watch for coolant drips, might take a while if you see any coolant coming down from inside the block then you got a cracked block and will need a replacement. I did this on my old 2004 and saw a very small drip starting between the block and the cylinder sleeve. It will be a slow drip while the engine is cold, the crack will grow as the metal expands when hot and dump more coolant into the oil.




Edit: Added the picture above. Sorry it s a little bad but you can just see the drip of coolant forming between the block and the cylinder sleeve. I did run Iron Tite through the coolant system and got another 6 months before the engine finally blew for good.

 

You might also want to inspect the cylinders, cracked blocks often leak into the chamber where small amounts can get burned off, hence the steam cleaned cylinder look... Might give you a clue as to what cyl to look at underneath. remove the spark plugs and use a cheap usb boroscope to take a look for anything unusual inside each combustion chamber.

I suppose it could all be going downward... In my case it was all going into the cylinder. I had a crack on one of the inner 4 cylinder walls though, so it could be different.