travlnman

I will check it out, it could just be the right harmonic under load to buzz the sheetmetal. Like I said, I can rev it to 4k sitting in the barn....no noise, and I'm reluctant to rev it much higher with it just sitting still. Thanks again, I will give it a look.

Have a '78 280z, all stock. The issue is this, when sitting still , I can rev the car to 3-4k with no issues or unusual sounds. However, when driving under load, if the RPM gets over about 3200 during acceleration, I get what sounds like either detonation or some type of valvetrain noise. It's very loud, and I am afraid to rev beyond this limit for fear of damage. Setting valve lash does no good, and it seems to have very little to do with timing, as I can increase or decrease timing with basically no effect. I am open to suggestions as to what it may be. Thanks in advance for any help you can give.

Okay, to resurrect an old problem. Please read the original post. This problem was nonexistent all summer long. I should also mention, that I'm in Alabama, and we saw upwards of 100deg F on a reg basis . No issues what so ever. It starts to get a little cool, and suddenly, I'm back to the same thing. If I let the car warm up to operating temp first, no problem, if not, pops the top on the overflow and pukes out coolant. And no, I have not even used the heat yet, the temp control has not been touched since last winter. Looking for suggestions.

ATF is a valid option, but it was not originally recommended by the factory. Many manual trans use ATF. Most modern ones do , and I've put nearly 500,000 miles on 3 different vehicles using ATF, but they were designed for ATF and it is recommended by the OEM. Redline stuff is good too, even better if you can find it locally without ordering online, which is not my favorite thing to do. Not sure how our old 4 and 5 speeds would react to pure ATF, maybe somebody will chime in that knows. Good luck.

Pennzoil synchromesh solved my cold trans problems. Thinner than gear oil, but thicker than ATF. Safe for "yellow metals" contained in some synchronizers . Since you are in a really cold climate, you could cut it 50/50 with ATF, thin it out some more. Try it straight first, it should show improvement.

Compression test results; #1 125 PSI #2 145PSI #3 150PSI #4 150PSI #5 145PSI #6 147 PSI Retested #1 after shooting a little 30 weight oil into the cylinder,and second test result was 135PSI So some leakage is happening on the rings. Opinions ? Comments ? Complaints ? Taking all kinds.

As I said in a previous post, drive before the t-stat opens, recovery tank lid pops off and pukes coolant everywhere. Drive after the t-stat opens, no problem.

Yeah, I hear that. The funny thing is, there is no overheating at all, ever. I have an aftermarket gauge that actually shows temp, and it's perfect, hovers just barely above 180 deg (the new thermostat rating) no matter what. I'm considering the radiator cap. The old original one was leaking, so I bought a new one. The new one is rated at 14 PSI. Not sure what original should be, but I saw new ones on a Z parts site (don't remember the name) rated at 7 PSI. Seems like my last Z had a single digit number (6 or 7 ) . I wonder if the higher pressure is just too much for the overflow to handle with the increased water flow of driving at a higher RPM while the t-stat is opening ? I may be grasping at straws, but it's worth a shot. I suppose it's also possible the cap is defective outta the box, as you correctly stated , many t-stats are. My head is sore from all the scratching....

Ok, it gets better. I have battled the overflow tank lid popping off and puking coolant. Thought this was an automatic head gasket. I kept testing other ideas. As it turns out , it only happens when I drive the car before the thermostat opens. I realize the thermostat does not just POP open, but opens slowly as it warms up. However, if I let the thermostat open completely before I drive, I can flog the car like I hate it, no lid pop off, no coolant loss. If I drive before it opens, I can drive like an old lady, and it will happen like clock work. Okay, I'm open to ideas. Thanks.

Could be a little heat soak going on, nearly vapor locking , and after the pump brings fresh cooler fuel up, it goes away. Just a thought. Also, make sure you are not losing coolant. If you are leaking into a cylinder, it will run rough until you purge all the water out.

I'll take that as a no...

I was planning on removing my head on my stock '78 today, in pursuit of a suspected blown head gasket. I removed the throttle body (don't ask me why) after removing the plugs and rocker cover, and discovered that it was soaking wet on the back of the butterfly. I had previously removed by BCDD , but still had the vacuum line to the EGR system attached. I was able to pour water from the bottom of my throttle body, in the orifices that lead to the now removed BCDD. There was no moisture in the area where the vacuum is applied to the rocker cover. The only source of coolant in the area it appears, is the vacuum line to the EGR system. This line leads to a valve that is temperature controlled, and threaded into a housing that has coolant circulating through it,and when it reaches a certain temp, it has a thermostat built in , and this lets vacuum go to the EGR valve . Has anyone ever had this valve fail in any way as to let coolant be sucked into the throttle body,and then the engine ? In a move that may be considered wishful thinking, I bypassed this valve by removing the coolant lines from the housing, and looping it back to the source. I really have no concern for the EGR functioning or not. I took a short drive after refilling my over flow tank. This had to be filled after each drive previously, and was still full on return. The drive was admittedly short, but I pushed it hard. The previous symptoms were: loss of coolant without obvious leak, all plugs showing residue that may be from coolant burn, when stop leak was added to running engine, when the thermostat opened , there was a small puff of smoke out the tail pipe that seemed to indicate burning of the oily residue of the stop leak. No, sadly, I did not check compression, but the car runs hard, and does not overheat at all. Just looking for previous experience and want to know if anyone has seen this before ? Sorry for the rambling and thanks for your replies.

Not sure on that one. Should be able to pick them up from Nissan. I would make sure I got the right thing. Electrical is not the place to be experimenting, hate to burn something out.

I just fixed this same problem today ! IT was not the switch in my case. It was the fusible link under the hood. There is one there, just for the lights. Mine had a dark corrosion on it. Five minutes with some scotchbrite, and voila' headlights work. Mine had become intermittent recently , working kinda when they wanted to. Last night, was at by bro in law's watching football, no lights to drive home . Found this problem today, so give it a look see. I had no current to the fuses, and certainly nothing at the switch, but my parking lights worked fine, tail lights worked fine. Sounds very similar.

Still no more problems. Have put many more miles on the car, and pushed it hard. No more coolant loss and no overheat issues. I know if the gasket was bad, it would not fix itself, so maybe just a giant burp was all it needed.