Coolant leak
 

Folks I am new to this forum. I have a 70 c-10 250 inline 6 which is original to the truck. Had the truck forty years. truck has run great all those years. Engine has never been apart. Recently I have noticed coolant seeping around cylinder head bolt #1 according to tightening sequence. Can't tell how many if any are leaking under valve cover. Did a cylinder leak test and pressure test on cooling system. Did not come up with definitive answer. I tried taking that bolt out to clean, chase, and seal threads with permatex 59214, did not help. Also tried permatex aviation form-a-gasket liquid seal on that same bolt and it's still seeping. If my health was better I would just start taking it apart till problem was found. May be too big of a problem for me to take on depending on what's wrong. Could someone with experience on inline 6's give me some direction?

Re: Coolant leak
 

I am wondering if it might be weeping from the upper or lower thermostat housing. It is right next to the number one head bolt from what I remember. Otherwise you might be looking at a head gasket issue. There and around #6 cylinder seem to be the common points if the were to leak/go bad.

You noticing any water in the oil at all?

Re: Coolant leak
 

The OP said #1 bolt by tightening sequence. I would assume that's what he meant. Meaning middle of the cylinder head no where near the thermostat.

Re: Coolant leak
 

I'm thinking it's time to pull the cylinder head and see what's going on.

Re: Coolant leak
 

Have not noticed any coolant in oil.but the bolt that I know coolant is seeping around is about a half a teaspoon .do not know I would notice

Re: Coolant leak
 

Yep did brain fart there.

Re: Coolant leak
 

You can buy a UV dye that will glow under a black light from any auto parts store. Put some in your radiator & drive the truck around a bit. Then check the oil on the dipstick with the black light. If any coolant is getting into the oil, you'll know. Then check around the head. You might be able to find a crack if that's what is going on. Might just be the head gasket though.

Re: Coolant leak
 

Yes I had put dye in cooling system about a year ago .so when hunting down this present thorn in the side took valve cover off and shined black light on ,it lit up like a city street.so it is like someone mention previously head is going to have to come off.what a pain it is odd that I am not seeing or smelling it on dip stick thanks for all the info folks.

Re: Coolant leak
 

Frank,
Noticing that you have had this truck for 40 years tells me you're like me, no spring chicken. I have a 51 with a 235 in it that I had the same problem. In my case I'm usually doing things by myself and that head is heavy. This is what I did and you may already know this. I lifted the head off with my cherry picker and reinstalled it the same way. When I reinstalled it I took a pair of old head bolts, cut the heads odd and tapered that end, then installed the head gasket, screwed one bolt in the front and another towards the rear. Then lowered it down with the picker onto the pins and it slide right into place, put a few bolts in then remove the tapered pins and you're good to go. These pins hold everything in place, worked great for me. Good luck, hope it's only a gasket.

Re: Coolant leak
 

Excellent hint old51sedan. After doing mechanic work for 51 yrs.i finally learned some of these little tricks.being my on boss I did not have to worry about all the not so smart things I did.thanks again for the hint.

Re: Coolant leak
 

Well great, didn't know if you knew or not, I learned that the hard way. Hopefully it might help someone else along the way. Good luck, so like you got it covered.

Re: Coolant leak
 

Thanks for the info

Re: Coolant leak
 

Back in the day, I had a minor leak from a partial crack in a intake manifold on a 265 V-8. Being a dirt poor college student and not wanting to pull the manifold, I poured some kind of metallic powder in the radiator, which stopped the leak 100%. I drove that car for another 6 months or so until I installed another engine, and I don't remember the leak returning.

If you google "cooling system stop leak powder" you'll get a lot of hits.

Re: Coolant leak
 

^ AlumASeal

Re: Coolant leak
 

Yes I have tried a block seal that I have used for years when that is what my customers wanted to try against my better judgement.i guess when you have back problems you will try anything to keep from removing head. And all the machine shops around here have shut down.may end up looking for a recently rebuilt stock 250.thanks for all the input folks.

Re: Coolant leak
 

Just don't get a later model 250 with the integral cylinder head and intake manifold that is prone to cracking. Some of those engines also had an emissions system called PAIR, which took the place of an AIR pump.

Attached photo is a 250 in an 82 C10. The chambers and plumbing on top of the valve cover are part of the PAIR system..

Re: Coolant leak
 

Thanks,for the info.

Re: Coolant leak
 

Possibly a hairline crack in the head. Or if the head bolts extend into coolant passages, maybe coolant is seeping up bolt threads. I've never seen it happen with bolts, but I have seen coolant leak up through head studs.

Re: Coolant leak
 

Yea mikeb there all bolts and all 14 go into water jackets.i tried permatex 59214 and permatex aviation form a gasket sealant liquid.thanks for thinking on it.