I have a 1981 Datsun 510 with 55000 miles on it. The engine has been running great for all the 4 years that I owned it. One day I had the bad idea to try synthetic oil, which made the engine to "click" once it was hot. A mechanic told me to put regular oil back as synthetic was too light. The minute after, it started to run perfect again. For the next oil change, I told the mechanics to put a thicker oil than normal. They put 20W50 as "an oil can be too thick" as they said. Since then, the engine started to do the same strange noise, comming from the valves area (I guess) that sounds a bit like a million knukle snappings. Now MY simple question is: can an oil be too thick?
There is a rumor going around that atleast with the newer nissan engines that making the switch from oil to synthetic causes problems with the engine seals. The general logic is this... gunk collects around the seals, synthetic with it's better flow rate cleans out the gunk and possibly the seal.
I am unsure how true this is, however I'd suspect that making the switch synthetic assuming it does indeed solve old oil gunk might have cleaned the valves resulting in greater noise if they are knocking. This idea is also based on my recent cleaning of my old toyota head and being able to hear one valve knocking much more clearly then before.
Personaly I would stick with what has been used in the past for the engine. Needless to say a valve adjustment would be prudent.
I was thinking the same. These cars need adjustment periodically.
BTW - AFAIK, 510's are still in very high demand on the race circuit. A car with the low miles of your is probably worth quite a bit to a rally driver. (Qualifier: I don't follow that crowd anymore so I may be off base.)
Yes, I would agree re: the "old" engine IF he said he had 155,000 miles on it, but he only has 55,000 miles...that's not "old" really. Not at all.
He didn't state if he had done regular and proper maintenance on his car -- like regular oil/filter changes -- all along. He's owned it only for 4 years, so that means there've been other owners...how many and what did THEY do or not do when they had the car?
But if he HAS done regular maintenance, then his engine at 55,000 miles probably is pretty clean internally. If he has NOT done regular oil changes, then how many oil changes DID he do in 55K miles: 1, 2,
12 or none? Need more information. He didn't say he had any previous leaks, either, so I doubt they MIGHT have been plugged by sludge the synthetic oil could have cleaned away (and sent to the filter, BTW...change filters always!). Bad/worn-out engine seals in 55K miles isn't likely, either.
I have two cars, a 1973 Datsun 1200 and a 1995 Nissan 200SX SE. The Datsun has been on Dino oil for 30 years (about 362,000 miles) and the Nissan -- when I got it at only 23,000 miles, just recently) was also on Dino oil. I changed the Nissan over to Mobil 1 ASAP but will leave the Datsun on Dino...partly for the reason you mentioned: It's an old engine probably with some seals/leak problems and sludge build-up here and there.
So as I said, I'd agree with you but HIS engine is not that old.
Besides, so synthetic oils will find engine leaks - probably true -- but an engine shouldn't be leaking regardless, so he would need to FIX the leaks anyway. It's not really the oil's fault and it's not because synthetic oil "messed up" his engine. Synthetic oils ARE better than Dino oils, especially for engine longevity, if you KNOW right up front you want to keep the car indefinitely use synthetic. Even if you don't keep the car, the next owner will benefit from it being on synthetic...raise your selling price more for that reason.
So I based my answer on what he did say: A 55K mile engine and valve noise. Assuming regular oil changes...I doubt synthetic caused any problems, he DOES need to BE SURE the valves ARE adjusted properly. Loose valves are better than tight valves but they should be in specs regardless.
But I'm no expert so the above is just my opinion, but at 55K miles, I'd go to synthetic motor oil right away (I even use Mobil 1 synthetic ATF in my AT).
I assumed that the engine was rebuilt (at least) at some point to have
55K miles on it -- it was a creampuff and ONLY had 55K miles on it previously, so again, it's almost like new. He didn't say "I've had this car 4 years and only put 55K miles on it but the previous owners put 100-200K miles on it earlier so it's got 155-255K miles total."
He just didn't say so I have to guess...I can only go by what he said. Most people don't give enough data up front.
If he DOES have 155,000K miles on it -- the engine's never been rebuilt since 1981 -- then that's another story...but he didn't say that, only that it has 55K miles. But again, the suggestion was that the synthetic oil "messed something up" or it was a "mistake" using it.
Don't blame the synthetic oil is what I"m saying...it's good stuff! And if you have leaks, fix them.
Regardless, the valves themselves need investigation, and if they've never been adjusted in 155K miles (?) then they are WAY WAY overdue!
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