Blown head gasket?

[Walter Moore]

I think that the head gasket on my 240 has let go.

Last weekend it was running rough and smelled like it was running rich, and since there was a club event this weekend I tried to "touch up" the SUs. I didn't have time to test drive it afterward but it sounded good at idle. Thursday morning I started to drive it to work so that I could take it to the club meeting that evening and it was running worse. I limped it home and spent that night doing a full tune-up and mixture adjustment. (I took the SUs all the way back to fully closed and did a full by the video adjustment.)

When I pulled the plugs, number 1 and 2 were covered in oil. As I was adjusting the carburetors I noticed oil on the head that seemed to be blowing up out of the number 2 exhaust port. (Apparently the header bolts are a little loose...) Then there was a pop, and smoke billowed up from under the header.

The car has not been low on coolant ever, and isn't low now. I did notice that it was one quart low on oil for the first time ever last weekend, but it had been over 2000 miles since the last oil change.

I drove it a little Saturday. It is way down on power, and chugs when it accelerates. (Kind of like it is running on 4 or 5 cylinders.)

I suppose that I could "swing a dead chicken" as they say in techie circles and run a compression test, but the timing is perfect, the mixture seems to be right, and it is blowing wisps of white smoke at idle that get more intense under load. There is clearly something wrong inside that motor, and I am not going to fix it without taking the head off at the very least. The only real question is: Do I pull the head with the engine in the car, or pull the whole thing out and rebuild the whole thing again?

Right now I am wondering how these engines can be so fragile..

[Bruce Palmer]

Walt,

With the engine running is anything out of the ordinary happening in the radiator with the cap off. Like the engine is pumping air into a cooling chamber. Oil look okay? Not milky?

[Walter Moore]

I haven't checked the radiator with the engine running. The oil was not discolored when I changed it a couple of weeks ago. (just the normal black)

Right now it is just slightly above the full mark and looks pristine.

One of my coworkers suggested that it might be a bad intake gasket causing two cylinders to lean out to the point of not running at all. I guess I need to do some more diagnostic work, when I have time.

[jmortensen]

Along the lines of what Bruce is saying about checking the radiator, you can also literally put a smog sniffer or an air conditioning leak detector in the neck of the radiator and sniff the hydrocarbons if it is blowing exhaust into the coolant.

The L6 is not a weak engine, nor is it prone to headgasket failures. There is some controversy about headgaskets, I always used a Nissan or Stone gasket. I fall firmly into the "don't use a Fel-Pro gasket" camp, but others who know what they're talking about disagree. If everything else is OK (if the head and the block are flat), you're not likely to have problems again. I wouldn't pull the motor to change a headgasket.

[Walter Moore]

If I was sure it was the head gasket I wouldn't pull the engine either, but at this point I just need to find time to check some things.

Thanks for the advice.

[ajmcforester]

To answer the question should I just pull the motor out. How many miles on the rebuild, if it has been a while you could freshen up the bottom end? Do you think you might need to replace piston rings?

I would not run the engine as much as possible. If you start to get water in the oil you might be taking that engine out to replace all the bearings.

[FastWoman]

You wrote:

"Then there was a pop, and smoke billowed up from under the header."

i.e. from oil spraying on your header? That would certainly be an indication of a blown head gasket. Do you see oil on the side of your engine?

I can't give you any good advice, as I've never dealt with a head gasket. All I can do is to wish you good luck and to say that I, too, have found these engines to be very tough/durable.

[sam280z]

If you were me, you'd do a leakdown test to start. It will tell you what's going on or at a minimum remove most possibilities.

Sam

[Walter Moore]

In the immortal words of Rozanne Rozannadana, "Neeevver Mind."

I don't have the tools for a leak-down test, but I did a traditional compression test and have no more than about 10 PSI difference across all six cylinders. Further, five of the six read higher than they did four years ago. Cylinder number 6 reads exactly the same as it did earlier.

I did find that several of the bolts and nuts that hold the intake and exhaust manifolds (headers) on were slightly loose. It took about 1/4 to 1/2 turn to bring them back to 8 lb-ft of torque.

I replaced the plugs, and I also added a vacuum port to the cross-over pipe, and used a vacuum gage to confirm my mixture settings. With a little experimentation I got it to read a fairly steady 13 inches of vacuum at idle. I took the radiator cap off and ran the engine hot. The fluid level rose up to the top of the filler and overflowed a little, but there was no sign of bubbles or turbulence in the fluid.

I drove it around a little this evening and it seems to run OK. I will have to drive it a little more, or a little harder to confirm this, but it looks like I over reacted. Oh, and the "oil leak" above the header is gone. It must have actually been leaking exhaust.

I did notice that I had WAY over oiled the K&N filter. (There was actually oil pooled in the up-side down air cleaner cover that was laying on my work bench for several weeks.) That may have been the actual source of the original problem.

:embarrass:

[SteveJ]

In the immortal words of Rozanne Rozannadana, "Neeevver Mind."

Actually it was Emily Litella who would say that after finding out that her latest rant was misdirected.

Of course, I think we've all done stupid things to our cars in the process of trying to break out of our zones of ignorance. Rockauto publishes confessions in their newsletter of people brave enough to admit how they messed up. One of the big inspirations for buying the 260Z was to prove that I had learned from all of the things I did wrong on the 240Z.