How to detect air manifold leak?

[mrfatboy]

I think a there is a leak that is sucking air into the manifold.  I remember a mechanic told me that you can spray "something" around the manifold and listen for RPM changes to locate the leak. What is that "something"?  Carb cleaner, wd40, etc? I wanted to hear from you guys before I did something stupid.

Is there a better way?

1969 280sl
Signal Red

[rwmastel]

Just a guess: starting fluid?  It would be like adding fuel and that would change the RPM, right?

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[Dick M]

DO NOT TRY THIS....
In the early 60s I was an auto shop teacher at a boy's vocational school in Isfahan, Iran... Common practice was to spray gasoline around the manifold.[:0] I ran the other direction but it worked.

Dick M
1970 280SL

[mrfatboy]

I definately would not do gasoline.  There is something else mechanics use but I can't remember.  I don't what to harm the engine.

I'm not sure but I think WD 40 would harm it.

anybody else?

1969 280sl
Signal Red

[merrill]

when I was having problems with my sl, hans at h&r said to use spray carb cleaner.  

by using the spray with the tube that comes with it, you can control how much and where the spray goes.

if you have a leak the rpm's will increase for a second or two.
(assuming the car is at idle)

Matt
Austin Tx
66 230 sl - "white"
78 300 D - Blue
98 C230

[mrfatboy]

I tried using spray carb cleaner for a little bit but then stopped because I was not sure if it was good for the engine.  Another guy that I know (not alot) said he had talken the Bosch F/I training program.  He said that carb cleaner was not a good thing and they used to use water.  Using water sounded crazy to me[:0]  Who would want water getting sucked into their engine?

That's why I am here asking the experts  

Btw, when I did use the carb cleaner around the manifold the RPM's lowered.  Obviously a leak but what does that mean over all?

1969 280sl
Signal Red

[hands_aus]

quote:Originally posted by mrfatboy

 Using water sounded crazy to me[:0]  Who would want water getting sucked into their engine?

That's why I am here asking the experts  

Btw, when I did use the carb cleaner around the manifold the RPM's lowered.  Obviously a leak but what does that mean over all?

1969 280sl
Signal Red

It stikes me that the small amount of water would do very little harm and it certainly is not flammable and it would achieve the same result.
Do one area at a time so that you can determine how many leaks there are.
If your vacuum lines and clamps are originals it is about time they were replaced.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[jameshoward]

Agree totally with Bob. Water isn't as mad as it might sound. There is a guy here in Germany who had an old machine that used to trickle in a mix of water and coolant into the pots via a vacuum hose to clean out carbon to improve compression/free things up. It was ultra low tech and you can achieve the same thing with a plastic fizzy drinks bottle just allowing the mixture to dribble in. I've done the same thing with BG44K to try to sort my compression and it does work. The water thing effectively steam cleans the engine on the inside(the carbon is dissolved in the mixture of gasses formed when steam is created in the compression chamber). It is well known that you'll never seen a cleaner engine than one with a leaking cyl head gasket (shortly before it all goes horribly wrong, of course). I would like to try the water thing but haven't needed to yet. The guy in Germany with the 'device' had it stolen when someone stole the old car it was attached to. (Typical).

There are several articles on the internet about using water to do this. The obvious potential pooh trap is hydrostatic lock, which would be a bad thing.

There is quite a lot on the net about this, and whilst it has nothing to do with manifold leaks (sorry) it is an interesting area. Here's an interesting discussion on the topic:

http://www.automotiveforums.com/t283211-water_cylinder_decarbonizing____should_i_.html

JH

[bpossel]

Some shop vacs have a blower port.  With a cold engine, blow air into the exhaust pipe (close up the other pipe with a rag).  Use a spray bottle with water and a bit of liquid dish soap and spray around the manifold.  You should see the soap bubbling in any areas that may have a leak.

Havent ever tried this, read this some time ago....  Make sure to remove the rag from the other pipe when done[:0].

Bob

bpossel  (Memphis, TN.)
'71 280SL  /  '97 E320

[Shvegel]

Carb cleaner works pretty well. Just be carefull of flamables near the ignition wires etc. I was working in a shop tha switched from non-flamible brake cleaner to an alcohol based "Enviromentally Friendly" cleaner. I was cleaning off some fingerprints from a running engine when I hit the plugwires my workmates said there was a tiny mushroom cloud under the hood.

My wife said I looked better with eyebrows.