Water over hood, now unknown tapping noise - PeachParts Mercedes-Benz Forum

sos3 · #1 09-23-2006, 05:59 PM

Newbie here, 91 300te 4matic, 250,000.
SO went through a wash here in New Mexico (only a foot of water) and washed water over hood. Car died, started 20 min later. Drove 6 miles. Air filter wet, radiator sensor apparently shorted out, no water in oil (drained after sitting overnight). Now have a definite tapping noise you can hear standing outside of car. Used tubing to ear all over but do not get any sign of increased noise corresponding to the tapping (valve cover, injectors, exhaust manifold, block, crankcase, tranny, peripherals). Have not pulled entire airfilter assembly for access to that side. Any thoughts?

Great informative site. Have learned a lot through searches. Yes, I know, 91 300te 4matic, run, don't walk away.
Appreciated,
Tom

deanyel · #2 09-23-2006, 06:23 PM

This is unscientific but I would put it in a warm dry garage, open the hood, point a huge fan at the engine for about 3 days.

t walgamuth · #3 09-23-2006, 06:29 PM

if you got the intake under water you may have sucked water into the engine and bent a rod.

i hope not.

i would have an experienced mechanic listen to the noise.

tom w

sos3 · #4 09-23-2006, 07:23 PM

As explained to me, the water was a washover, not a submersion. The air filter wetness shows some indeed in the intake area.

If a rod, should I be able to isolate the location through stethescope, tubing technique?
What's bugging me is that I can't find the location of the noise and obviously don't want to drive it until I know what it is.
Maybe time to get the 86 xj6 radiator.
Thanks for your help.
Tom

MikeTangas · #5 09-23-2006, 11:24 PM

I have heard a shorted plug wire make a definite tapping sound before. Think of the sound of jumping spark. Perhaps wet wires have uncovered a bad set of wires. Just food for thought.

t walgamuth · #6 09-23-2006, 11:57 PM

i am not sure how to determine it.

i bent a rod in one of my 6.2 gm diesels when a glow plug end broke off. the symptom was a very loud diesel like sound.

tom w

sos3 · #7 09-24-2006, 12:04 PM

the sound is not a real loud knock (yet!).
Drove the car about 3 miles - smooth. Have revved the engine in park to 5000- smooth. Idles smooth. Tapping frequency increases and decreases with engine rpm. Loudness level never changes. Oil pressure good.
Will check wires - good thought.

Plan to pull air filter assembly for better access to intake manifold side.
Thanks,Tom

ILUVMILS · #8 09-24-2006, 12:41 PM

The first thing I thought of when I read this post was a bent connecting rod. Do a compression test. If you've got a bent rod, the affected cylinder will have noticably lower compression. How much lower depends on how badly the rod is bent. If you do have a bent rod (I hope you don't), the noise you hear is most likely the rod hitting the bottom of the cylinder. Good luck

t walgamuth · #9 09-24-2006, 12:53 PM

it could be bent only slightly. if so then a compression test may not reveal a big difference. any amount of rod being bent should show something on a comp test though. though the normal variation of the cylinders could mask it.

on a diesel 1.5 teaspoons of water will fill the combustion chamber. so with a gasser of similar displacement a bit over twice that amount would be needed. so maybe 3.2 teaspoons (or is it cubic inches?). but you get the idea, a full cylinder will not allow the engine to turn over under cranking. so a partially filled cylinder may. anything over the volumn of the compressed combustible material will result in a bent rod of some magnitude.

it is a tricky little question.

good luck

tom w