coolant in #3 intake

[akorna]

I have been troubleshooting a recent rough idle and hesitation. Everything checked out fine, but vacuum was only about 10-12 Hg at idle. I tracked down an intake leak at the head at the #4 cylinder. Knew I had to replace the intake/exhaust gasket, so removed everything. After I had the intake manifolds off, I could see in the head that the valve (closed) was in a pool of coolant! I have 175 psi compression in that cylinder and no sign of coolant in the oil, or oil in the coolant. The plug had looked like the mixture was running a little lean, but similar to the other plugs. The engine has not had white smoke coming out the exhaust. I wonder if the coolant leaked in from the manifold ('72 w/water cooled three screw Ztherapy SU's) during disassembly or am I looking at a cracked head? Anyone experience something similar?

[Nissanman]

I tend to think that the coolant got there during your dismantling work:ermm:

If you measured 175psi compression in #4 then I'd take that as a good sign.

I would put it all back together with the new manifold gasket and see how it goes.

When/if you see that it runs OK, do a Leakdown Test on an engine that is at operating temperature.

That is really the only thing you can do IMO, apart from ripping the head off now, which I don't think is necessary:beer:

[bobc]

Joe, you didn't say if you drained the radiator before taking off the manifold. If you did, it's even more unlikely that the antifreeze got into the number four cylinder when you removed the carb/intake set up. If you didn't there may have been enough pressure just from the weight/height of the water in the radiator to push water out of the manifold cooling pipes (either end) when you removed the hoses. Did you notice a lot of water coming out when you removed the manifold cooling hoses? Did you already have the hoses off before you loosened the manifold?

I tend to agree with Nissanman that if you didn't have any other symptoms, I'd put it back together and perform a leak down test.

Best,

Bob

[akorna]

Thanks Nissanman/Bobc,

Note that the vacuum leak was at the #4 Intake, the coolant was visible in the #3. I did not drain the radiator, but rather removed carbs, then disconnected the hoses at each intake - so there is a chance that it leaked back into the head. I think I'll go ahead intall a new Intake/Exhaust gasket w/new hardware and re-assmble everything and post what happens.

[Bruce Palmer]

While you are putzing around with stuff, check to make sure your insulators aren't cracked around the coolant holes into the carbs. That could be a source of coolant into the engine. It might be getting into all 3 of those cylinders, but only showed up in 3 because those valves were closed.

Don't even want to think about a crack in the head in that intake runner but see what you can find and let us know.

[240260280z]

I had cracks develop n a head but I would notice intermittent coolant loss. The cracks were on the exhaust runner roofs in an N47 head. The plugs also looked crappy and crusty.

http://atlanticz.ca/zclub/techtips/head/crackedhead/index.htm

[akorna]

All - thanks for the advice and observations. I re-assembled the entire intake and exhaust manifolds using new gaskets, pcv valve, pcv hose, and thin beads of copper silicone sealant. While I had the exhaust manifolds off, I removed all of the air injection plumbing, and blocked off the holes with 14mm X 1.25 bolts (installed bolts with sealant, then cut off bolt heads and ground close to flush with the manifold. I also replaced the exhaust manifold to exhaust pipe gasket. The exisiting one pretty much crumbled apart during disassembly. I had two studs fail, the far forward exhaust stud (enough thread left that I was able to double nut and drown in PB blaster and remove) and the far rear (had to drill and insert). I baselined the car settings and let the sealant cure for 24 hours. On restart, it fired up quicker than I expected. I slowly released the choke, and was able to get it to idle pretty well at about 1000 rpm - much smoother than before. I was pleased to see that vacuum was now 18-19 inches of mercury, instead of the 10-12 earlier. I synchronized the carbs, left the mixture alone for the moment and test drove - seemed much better. This coming weekend I will set mixture and check for any evidence of coolant loss, but I'm pretty sure the head is fine. Likely the coolant got in the intake during disassembly. Attached are before and after pics.

Before

After