About 8 months ago my 77 280 developed a coolant leak at the head gasket between 3 and 4 cylinder. I used a good quality stop leak and it did slow it down however, while I was working on my "leaky injector" issue I found another coolant leak. This one is near the firewall below the #6 exhaust port. It's about and inch forward of the corner of the head. Here is a pic. I guess with this new coolant leak I should consider doing a head gasket soon? Attachments_201532.zip

 

Almost forgot one important thing. It starts leaking on cold start up and stops once the engines comes to temp.

Edited March 3, 201510 yr by rcb280z

Those pics aren't that great so tomorrow I will try and get better ones.

Its not too surprising it quits leaking after warm up due to expansion of head and block. Probably pinches head gasket tight enough that it doesnt leak when hot. I take it that you have no other symptoms...Pressure build up in radiator,or white steam cloud out of exhaust?

i vote to do the head gasket and while you're at it pull the freeze plugs and flush out the block to get rid of all the crud in there - you will feel so much better knowing it's cleaned out. 

and while the head is off you can clean out the chambers, which is also a very nice feeling!

 

it's not that hard and when it's done there will be no more leaks, no more crud.

Maybe snugging the head bolts up would help until you're ready for pulling the head off?  When I tore down my 2.4 a couple of weeks ago I was amazed at the difference in effort to remove some of them.   

careful re-torquing head bolts if they haven't been touched in a couple of decades... first time i took my head off on of them snapped and 2 others almost did. they get frozen from corrosion and having gone through a whole lot of heat cycles get brittle. if you pull the head, get a new set (courtesy nissan has the turbo ones for ~$60 a set) and be worry-free.

Crazy, I hadn't thought about checking rad pressure. Will have to investigate this. No steam out the exhaust after a couple minutes of cold start up.

 

rossiz, I'm considering replacing head gasket. I have a Stone HG. Just need the other gaskets. Plus flushing everything to get all that stop leak out. Will probably have it flushed out before tearing it apart. 

 

siteunseen, that was going to be my plan, re-torquing head bolts but after research found that this may not be the best thing on bolts that haven't been messed with for over 20 years. So I guess I have to pull the head. I really don't want to do this right now. I did a compression test a few months back and found 2 cylinders about 20-25 psi lower than the others. They are not adjacent cylinders. But if I have to pull the head I may as well pull the whole motor and go through it. Or am I just doing unnecessary work? I did a "light" overhaul in '91 on this motor. Rings, main and rod bearings, valve seals, just the basics and it has over 100k miles since then. So it's time, I think, to go through it. What to do, what to do...

pulling the head and replacing the head gasket can be done in an afternoon - depending on how much resistance the manifolds give you. that's the big unknown as far as my experience goes. that and if head bolts snap. putting it back together goes much quicker - provided you take care with your cam chain tensioner. losing that little bugger turns a sandwich into a banquet, if ya know what i mean...

 

as for flushing the block, you can do some with it all together, but i found a ton of sludge in the two blocks i've taken apart so far. the one in my car i pulled the frost plugs and used a pressure washer to blow down into all the passageways in the block and mounds of crud came out of the frost plug holes. i even used a coat hanger to reach in through the frost plug openings and scrape out clumps of goo. your's may not be as bad, but i doubt i would have been able to clean the block out like that with the head on it.

 it has over 100k miles since then. So it's time, I think, to go through it. What to do, what to do...

Has it ever overheated in those miles?  The aluminum heads don't like overheating.  Depending on your spare parts pile or availability, maybe it's time for another reworked head.  Then you'll have a spare to dink around with.

Never overheated. It used to run just past the half way mark I'm thinking like around 195. I now how an aluminum radiator and it runs dead center all the time.

 

So you think I could leave the bottom end alone? I had thought about it a couple of times.

 

I only have a P79 that has heavy gouges in the mating surface. It's ugly. But the cam, rockers, springs, everything looks really good. Even the valve stem seals look new. Picked this head up from a friend who was going to toss it out! Was going to do the P79 on a N47 with flat tops but changed my mind. Thought it would be even harder to pass the CA emissions if I did it. Anyway, guess I could transfer all the stuff over to my N47 head right? Or are the valves a different size? I can't remember off hand.

 Mechanic friend of mine checks valve leakage with the head off by tipping the head port side up. Any port that has a closed valve gets solvent poured down the port. If a valve is leaking, you'll see it fast in the c-chamber. At that point he pulls the offending valve or valves. If everything looks OK, he laps the valves & seats & checks again. I'd eliminate leaking valves as a reason for the low comp. before I tore the whole thing down. Unless you have the time, money & desire to do so.

Good advise Mark. Thanks. Have to think about what do to do next.

 

Don't really feel like doing the whole motor. But will if I have to.