black gunk in the coolant system...?

[kcducttaper]

I did my standard oil change today and noticed some black gunk on the bottom of the radiator cap (which is about 2 months old). I stuck my finger down the radiator and, sure enough, it had black goop coating it too.

I rebuilt the motor just 6 months ago and dumped new fluids in (same as what came out), so the coolant should be good.

Ever since I rebuilt the motor, coolant has been backing up into the reservoir and I have to drain the coolant back into the system about once every week or two. I've replaced the radiator cap, reservoir tube, and thermostat to no avail.

I see no visual evidence of oil in the coolant itself, or vise-versa with coolant in the oil. Everything is the correct color and viscosity. I could see a head gasket problem causing all this, but it seems like I'd be seeing fluids getting mixed up if that were the case.

Any of you pros got some ideas for me? I might just run it into the ground as it's a rusty '94 Villager and has 320,000 miles on it. Plus, I'm just sick of staring up at it from underneath.

[maxwedge]

First thing to do is figure out what this "goop" is. You could have it analyzed at one of the oil analysis labs.

[Crvett69]

if its oil you may have a leaking head gasket or cracked head, would also explain the coolant backing up into reservoir. it could also be a hose inner part coming apart but i would be more inclined to think its oil. have you had to add any water? you can also look at the bottom of oil fill cap for moisture. i know the 4 cyl neons were known to get oil into the cooling system and bubbles in the overflow when you shut it off. they had leaking head gasket problems

[kcducttaper]

Yeah, I've thought about the head gasket thing and if perhaps I cracked the head gasket putting it on or something. The only thing is there is absolutely no trace of oil in the actual coolant liquid itself, nor water in the oil.

[Crvett69]

did you replace the head bolts when you did the head gaskets, lot of them are a one use only type

[kcducttaper]

Originally Posted by Crvett69

did you replace the head bolts when you did the head gaskets, lot of them are a one use only type

I knew they were "supposed" to be replaced with new ones, but I didn't think it would matter much if I threw the old bolts back in there (cleaned up of course) for such a low power application for another year or two. Although that does get me wondering if my torque wrench is calibrated properly...

[shorod]

The "torque to yield" head bolts stretch when torqued properly, the first time. Yield and Fracture are not quite the same thing, but usually a fracture closely follows the yield. So reusing the bolts is not good practice.

-Rod

[Crvett69]

why did you rebuild the engine to begin with? also did you have the heads rebuilt and did they surface them?

[kcducttaper]

I definitely wouldn't have thrown the old bolts back in if I were going to keep it for several more years, but I didn't want to make another hour long trip to the parts place and I only intend to keep driving it for another year or two, so I figured what the heck.

So, you're thinking a head bolt may have broken off recently and there's oil getting in the coolant system? If that's the case, then why am I still not seeing any discoloration of the coolant or oil?

[Crvett69]

i doubt one broke off but once they are stretched they don't always go back to original length when removed and they when they are reused don't have the same elastic holding stength when reused so don't clamp the head on as well. if they suggest you get new ones thats usually the reason why. new bolts are cheaper than having to do the job over and get the heads planed again

[kcducttaper]

Ok, I've figured it out and you guys were on the right track. However, it has nothing to do with oil, but I think combustion gasses are getting into the coolant system. It's hard to say if it's from old head bolts, a bad gasket, or what, but I'm pretty sure that's what it is now after having another look at it and some more analysis.

[Crvett69]

you can get a kit to check for combustion gasses in the cooling system. you can buy them at local parts store or on amazon and other asorted places. here is video of someone using it
https://www.youtube.com/watch?v=ON_RtokUohI

[kcducttaper]

Yeah, I might be picking one of those up sometime soon. I wonder if you can rent them for any cheaper...?

[kcducttaper]

oof....no need for the gas kit. I poked my nose in the radiator last night while I was refilling it and was nearly knocked clean on my butt - definitely exhaust gasses in there, no question about it. My nose is still recovering and may look like a pickle for the next couple days.