We bought our 88 coupe automatic in 89 with about 15,000 miles on it. It now has 183,000 miles on it. The heads have never been off. The intake manifold gaskets were replaced once. It has been driven mostly freeway by my wife with very little "spirited driving". I did all the oil changes myself using Pennzoil 10W-30 and a premium filter every 5,000 miles. It puffs a little blue smoke during cold start-up. It uses approx. 1 quart every 5,000 miles. It still runs strong and passes Califiornia smog tests (punched out pre-cats and new main cat). It still gets 24 to 26 MPG on the freeway.

Lately, I am hearing some new sounds from the engine. One sound happens when the throttle is bumped quickly (in park) or when pulling away from a stop. It sounds like an exhaust leak but I can't feel any exhaust around the various connections.

The other sound seems more serious and may or may not be related to the first sound. It is a faint but unmistakable knocking sound that occurs when the engine speed is held at about 1100 RPM (in park). Raising the RPM slowly will cause the knocking to stop until about 1900 RPM. Oil pressure is around 50 PSI (not fully warmed up). It doesn't have that deep rod knock sound. Wrist pin maybe?

Here are my questions: Can a timing chain make that knocking noise? Is there a way to prove or disprove a bad timing chain without pulling the cover off? How does an engine this tired typically die? Is it time for thicker oil?

Thanks in advance for any feedback or comments.

 

With that kind of mileage the L98 is getting a little tired. My first place to look would be the lifters. The cam and lifters are surely worn enough to cause slack in the push rod causing a slight rattle/ticking noise. Replacing the lifters is relatively inexpensive.....especially if you know how to pull an intake off and adjust valves.

 

As to the front, exhaust like noise, I'd suspect that one of the check valves on the headers or to the cat in the air pump plumbing may be bad. It could also be that the air pump control solenoid is defective, exhausting air into the diverter pipe that's just in front of the waterpump. It's a little to dicey to stick your hand down there to feel for air with the engine running. A better method is disable the fan and then jack it up. Then crawl underneath and with the engine running, see if you can feel an airstream on your face or extended hand just to the right of the waterpump.

The knocking noise could be the precats. Try tapping on them and see if there's anything rattling around inside.

 

I had a the same noise or knock that you are having, It did sound like a rod and the noise stopped with any increase in rpm. Also when I shut the engine off I would hear a clunck, it turned outto be a cracked flex plate. With that many miles if it has the stock flexplate I would check that asap.

 

My Vette is an automatic. Is the flexplate and the flywheel the same thing? I can't picture what a flexplate looks like. I took the torque converter cover off (4 screws) and did a visual exam. Nothing looked suspicious. There were no loose bolts or scraping marks on the flywheel or the torque converter.

My dad loaned me his automotive stethoscope. I will see if I can use that to isolate the knocking sound.

Thanks for the feedback.

Greg

 

It sounds like time and mileage are creeping up on it. Like on mine (and me). I have an '84 with 160,000 miles including 700-800 quarter mile passes. Mine, also has never had a head off. This spring I replaced the valve stem seals and the timing chain and sprockets. Your, "It puffs a little blue smoke during cold start-up." is valve guides and /or seals. New seals will help, but the valve guides are worn and it heeds a complete, thorough valve job. One quart in 5000 miles isn't enough. It should burn that much new. Did you mean, 500 miles? A change to 10w-40 would help a little. I checked my timing chain and decided to change it. I did my check with the distributor cap off. I ran the engine up to TDC on the timing marks, and then turned the engine backward. I stopped turning when I noticed the rotor in the distributor starting to move. I then, noted the timing marks to determine the slop in the timing chain. In my case, I got 12* of crank movement, before the rotor started to turn. Figuring that was horrible, I bought a new timing set and gaskets. It's not a small job, but I got her done. I was really pissed when I saw the old timing set. There was nothing really wrong with it. Sure it was loose. The chain had some slop, but there were no missing nylon teeth off of the cam sprocket. Except for some wear and tear, it was great. If I had x-ray vision, I never would have touched it. In short, don't mess with the timing set if it ONLY has 12* of slop, or so.

If I were you, I'd do a compression check and a cylinder leakage test. My compression is great, and the car keeps running quicker quarter miles. Obviously, the time IS coming, for both of us. The question is how soon, and how you want to prepare for it. Piecemeal repairs like a timing chain here and a valve job there, only puts off the inevitable, and wastes money in the process. Either buy a core and build it "your way" while you have the luxury of some time, or save up to buy a crate engine and prepare to do it right. Good luck, and...

RACE ON!!!

 

Yep that is the flywheel. This was on my 87 with the 700R auto and it was cracked around the holes for the bolts. Good luck.

 

That was not a typo...my Vette uses about 1 quart between oil changes (5,000 mile intervals). I never have to add any oil between oil changes. When it was new, it used about 1/4 of a quart between oil changes. I agree that patching the engine as each part fails becomes an exercise in futility and a waste of money at this point.

I'm leaning toward buying a GM crate engine (called ZZ4?). GM certainly did an excellent job with the original engine, so they deserve first consideration with the second engine. My wife drives our '88 coupe most of the time and she is quite happy with the available power. Her favorite trick is when some guy tries to prevent her from merging onto the freeway in front of him, she hammers the gas. At that point he has no further control over where she merges. 8~)

I do like your way of checking timing chain slop. Your 12 degree reference is helpful too. Did you happen to check how much slop you got after installing the new timing chain?

 

Excellent advice CFI- EFI . You said it all!

 

I would concur with the rest of the group - at 180k miles, the engine is tired.

Going crate would be a good option... the ZZ4 could be dicy to pass emissions, tho, cause the engine itself isn't smog legal. However, they may never notice!!!!

 

I can only imagine what the internals look like after 183,000 miles of Pennzoil.

 

As a matter of fact, I didn't. Because, without checking, I know it is as tight it's supposed to be. The double row, roller, set I put in there is as tight as the wire for high "C" on a piano. I would guess it's 2*, maybe 4*, tops. About the only two places left for slop, between the damper and the rotor, are the cam bearing oil clearences, and the backlash on the camshaft/distributor gear set.

RACE ON!!!

 

flyersfan1088 said, "I can only imagine what the internals look like after 183,000 miles of Pennzoil."

I don't want to start a new thread on oil preferences, but, for what it's worth, I took a look inside the valve cover through the oil filler opening. There is not one bit of sludge or varnish buildup visible through that hole. Nothing but shiny, clean rocker arms!

I stuck with Pennzoil because that is what I started with back in 1989. As far as conventional oils go, I doubt if it is much worse or better than the other brands. When I bought my 96 Impala SS new, I immediately drained the factory fill of dino oil and filled it with 10W-30 Mobil 1 synthetic. It is now at 145,000 miles and has seen nothing but Mobil 1. I figured if GM is putting Mobil 1 in all new Vettes, it's good enough for my Impala.

When the L98 in the Vette gets replaced, it will only see Mobil 1.

Thanks for the feedback.

 

I don't think that for regular duty, the oil really matters as long as it's changed on a regular basis.

 

She needs a fresh engine. Lots of things to consider...rebuild and keep her original or pull the engine, set it aside in case you want to put it back in someday (rebuilt of course) or install a crate 350/383 and give her some throttle response

Frank

 

Pennzoil is parafin based. Think of it as pouring candle wax in your engine.

 

I don't think much of Pennzoil, either, but I have to agree with bogus.

RACE ON!!!

 

Now I feel dumb. I took another try at finding what sounded like an exhaust leak. Then I remembered that about a year ago I replaced the exhaust manifold gasket on the driver's side because I had to pull the exhaust manifold off to get the flange re-welded. Since then, I never re-torqued the manifold bolts. I checked them this weekend and they were barely finger tight. I re-torqued them and no more exhaust leak! Duh!

BTW...one last comment about Pennzoil. I have no interest in defending Pennzoil - now I prefer Mobil 1. But, if Pennzoil was so inferior to other oils, how did my Vette's engine make it to 183,000 (and still going) without the valve covers or heads ever being removed? The timing chain cover has never been removed either. And, if Pennzoil was so bad, how come I'm only using 1 quart in 5,000 miles? I would think that "wax" must be some pretty good stuff.

It's hard to argue with success.

 

There are many ways to skin a cat. The same holds true for the lubricants oil manufactures put in their engine oils. Changing oil every 3000 miles is a good thing. The mineral oils that use wax will build up in an engine over time if you don't change your oil often.

How many of us have pulled an engine apart under those conditions? It isn't pretty. Especialy when an owner has a car that burns oil and all they do is add when its low and never change it.