2000 Rodeo engine tapping

Greetings from a rank newbie who doesn't even have an Izuzu...
The husband of one of my wife's co-workers called today for help with his recently purchased 2000 Rodeo. (I can't believe I am involved, but that's
another story.) He bought the Rodeo from a private party a couple months ago, and last night it developed a worrisome tapping sound. The problem was not apparent when he started his five mile trip in town but he heard it when he parked. The sound has not changed in intensity, and is the same warm as it is cold.
I met him at a local parking lot, and he's right: it is loud and worrisome. It is a sharp, light tap that is twice the rate of a rod knock and doesn't have the deep thunk that rod knocks have. It is plainly audible fifty feet away under conditions that carry a voice only twenty feet. The sound is much louder under the engine than above, and remains the same when I disable cylinders one at a time. The oil level is decent (1/2 qt low) and the oil appears to be a couple months old - probably changed before it was sold.
I advised him to mimimize his driving and stay off the freeways until he could get it to a real mechanic to determine exactly what is knocking. I'm concerned a rod end cap may have broken at one end.
Does any of this ring a bell?
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The following was posted here quite a while back (I saved it):

Personally, I've used nothing but a good synthetic since 1978, and my wife's 2004 Rodeo only has that problem when it's coming time for an oil change. I only change every year or 25,000 miles, due to the quality of synthetic I use, though filters get changed every 6 months or 12,500 miles. I use a 0w30, and once the oil has been changed (along with the filter, of course), the problem goes away very quickly (presumably the oil passages get cleaned out, since good quality synthetics do a nice job of cleaning, also).
You might want to try a good engine cleaning (with a QUALITY, mild engine cleaner), and try a 0w30 good quality synthetic such as Amsoil (yes - I'm biased - I've been using it for nearly 30 years and have results that fully justify my bias//and no, I don't sell it or work for the company). Just be cautious with a synthetic if the quart low oil is due to usage, rather than just a slight under-fill at the last oil change. Sometimes if an engine is using oil, it uses it "even better" upon switching to a synthetic, ironically because of the excellent cleaning properties of a good synthetic. Since your wife's friend's vehicle is a 2000, that might be a factor - check the mileage first before considering the above idea. Personally, if it was moving toward 100,000 miles, I'd be cautious switching over to a synthetic. But if it's been regularly changed, is tight (i.e. no leaks and no significant usage between changes), I'd say give it a try before spending a lot of money on it. Just don't let it go too long, so it doesn't cause a more catastophic failure (i.e. big $$$).
Oh - also if the vehicle has been almost exclusively an around-town, low mileage vehicle, I'd change oil and take it out on an interstate or major highway for 50-100 miles, then see what's happening with the noise. My wife's Rodeo is very sensitive to severe-service (i.e. around-town driving almost exclusively), and makes all sorts of noises after a while. A freeway trip of 100+ miles and it quiets down and gas mileage leaps up.
Good luck. Hope this helps and it's not a major engine problem for your wife's friend.
C.R.
On Sun, 16 Dec 2007 11:47:51 -0700, "Michael Pardee"

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Thanks to you and miles, C.R.
I was wondering about the valve train (because the tapping was about the right rate for that) but figured that the concentration of noise at the bottom of the engine pointed to bottom end trouble. I'll certainly pass along the recommendation for 5W-30 synthetic. I know the increased detergency reputation of synthetic is controversial in some corners, but I'm a believer. Combine that with the onset of winter and it's a no-brainer.
I was talking this over with my partner, who was an apprentice Audi mechanic before he got into technical fields. He suggested the engine may have experienced oil starvation and was shimmed or otherwise patched before it was sold. I remember when I was underneath the engine the pan gasket was hidden by red sealant, but I didn't really give it much thought. I hope that's not what the deal is.
Mike
wrote:

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On Wed, 19 Dec 2007 20:16:49 -0700, "Michael Pardee"

Mike,
Note that both Miles and I suggested the 0w30, not 5w30. The bulletin he referenced specified Mobil-1, but I would not hesitate to consider the Amsoil 0w30 also. That's all I run in all of our vehicles since Amsoil first introduced it. It's got the hot as well as cold weather protection. The bulletin Miles referenced spelled out the reasoning in details that I was not familiar with. Good post.
As for controversy with respect to "detergency reputation of synthetic" oil, I have not heard that previously - other than if a high-mileage engine is "sealed" by sludge and varnish after rubber gaskets and seals harden or crack, introduction of a good synthetic will "create" leaks by removing the unintentional sealants (sludge and varnish). That's certainly not a fault of the oil, just a fact in the engine (ironically probably due to the owner not having changed oil and filter regularly throughout the life of the vehicle). Synthetic oil is not a cure-all for every problem. It assumes the engine (or transmission, or whatever part) is in sound condition in the first place. If not, it's not worth putting in the initially-expensive oil until or unless the repairs are done first. Other than that, I know of no downside to good quality synthetic oil if used as directed and intended. Though usually more forgiving, synthetic oil can be misused and abused just as petroleum oil can be.
C.R.
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Michael Pardee wrote:

The Rodeo's are known for a tapping noise but not as loud as you describe. Often its the injector packs rather than lifters that make the noise but again, not nearly as loud as you describe. Most that have had troubles with lifter noise have cured it by temporarily changing to a 0w-30w synthetic.
Below is a TSB I found relating to this issue.
Engine Valve Train - Ticking Noise TICKING SOUND FROM HYDRAULIC VALVETRAIN
SERVICE INFORMATION
Condition: The above affected vehicles may exhibit a condition of ticking sounds coming from the valvetrain during normal operation.
Possible Cause: One or more hydraulic lash adjusters do not fully extend due to varnish build-up inside. This condition results from exceeding the required oil and filter change intervals. Severe driving conditions require more frequent oil and filter changes. (Refer to appropriate Owner's Manual or Workshop Manual for details.)
Correction: A typical repair for the condition may involve the replacement of the affected rocker arm(s), and rocker shaft(s). However, follow the information in this bulletin to perform an oil/filter change using 0W-30 Mobil 1 synthetic engine oil, prior to replacing any valvetrain component.
NOTE : Although the current recommended engine oil for these engines is 10W-30 API SJ, the 0W-30 synthetic engine oil allows air in the hydraulic lash adjusters to bleed out quickly and removes the varnish that is preventing hydraulic lash adjuster piston travel.
Service Procedure 1. Drain the engine oil, replace the oil filter with a Genuine Isuzu oil filter, and refill the crankcase with 0W-30 Mobil 1 synthetic engine oil.
2. With the engine warm, run it at 2,500 rpm for 30 minutes.
^ If the ticking noise goes away, return the vehicle to the customer.
^ If the ticking noise persists, proceed with step 3.
3. Let the motor run at idle and use a stethoscope or Steel screwdriver to determine which bank is noisy. Once you have determined the location, turn the key off. (Figure 1)
4. Remove the cylinder head cover on the noisy bank.
5. Inspect each rocker arm for clearance at the valve (when the rocker is on the base circle of the cam and the valve is closed). The noisy rocker arms are the ones with clearance. (Figure 2)
NOTE : Each cylinder head has one oil pressure relief valve that controls oil pressure to its rocker arms. If all rocker arms on one cylinder head have clearance and/or the rocker arm pivot shaft is worn, then the cylinder head oil pressure relief valve may be stuck open. In this case, refer to the appropriate Workshop Manual for additional troubleshooting procedures.
6. Remove the ticking rocker arm assembly, and inspect the wear pattern of the hydraulic lash adjuster surface that contacts the valve stem (the intake rocker arm is located under the camshafts, which require timing belt removal).
7. Carefully remove the Hydraulic Lash Adjuster(s) from the Rocker Arms using your fingers. (Figure 4)
IMPORTANT : Do not damage the O-Ring on the outside of the Hydraulic Lash Adjuster, or you will have to replace the entire rocker arm (the Hydraulic Lash Adjuster cannot be ordered separately). When replacing an exhaust rocker arm, replace its intermediate rocker arm too.
8. Insert a paper clip into the hole at the top of the Hydraulic Lash Adjuster and depress the spring loaded check ball, while completely pushing in the piston at the opposite end. Some traces of oil may come out of the check ball hole. (Figure 5)
9. Carefully remove and retain the Hydraulic Lash Adjuster O-Ring. Spray the Hydraulic Lash Adjuster piston with carburetor cleaner to remove any varnish (while holding the piston in). (Figure 6)
10. Submerge the Hydraulic Lash Adjuster in new cleaning solvent; (while depressing the check ball) pump the piston repeatedly to allow the cleaning solvent to penetrate through the Hydraulic Lash Adjuster. (Figure 7)
11. Submerge the Hydraulic Lash Adjuster in clean 0W-30 Mobil 1 synthetic engine oil, (while depressing the check ball) pump the piston repeatedly to allow 0W-30 Mobil 1 synthetic engine oil to penetrate through the Hydraulic Lash Adjuster. Then allow the piston to extend fully, to fill the Hydraulic Lash Adjuster with oil.
12. Reinstall the Hydraulic Lash Adjuster O-Ring.
13. Lube the Rocker Arm bore that houses the Hydraulic Lash Adjuster with 0W-30 Mobil 1 synthetic engine oil, then push the Hydraulic Lash Adjuster back into place.
14. Inspect for leaks at the check ball and piston by attempting to compress the Hydraulic Lash Adjuster without depressing the check ball (The Hydraulic Lash Adjuster should not leak or compress).
NOTE : Oil filled Hydraulic Lash Adjuster will hold its valve off the seat for several crank revolutions. This may cause the engine to run rough for a short period after starting. To prevent this, select one cylinder and bleed some oil off the Hydraulic Lash Adjuster (depress the Check Ball and compress the piston 1/4 of the way down). This will allow the valve to close. Do not remove all of the oil or the valves spring and cam will collapse the Hydraulic Lash Adjuster permanently.
15. Reassemble the engine using new cylinder head cover gasket (see Parts Information) and apply some gasket seal at the corners where the cam tower gasket and cylinder meet. Torque the Cylinder head cover bolts to 8 Nm (69 lb. in) using hand tools only.
16. Start the engine and listen for noise.
17. Remind the customer, "More frequent oil changes can prevent varnish accumulation." Also recommend to use minimum oil rating of: API Service SG, but SJ is preferred
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