Re: merc 850 tell tale
Actually it does have a telltale but not quite like later models. There's no hose attached, it comes directly out of the bottom of the block, thru a hole in the lower cowling and discharges on the port side of the motor, aft. Easily seen if you tilt the motor up and stand on the port side. Look upwards at the lower cowling, above the wrap-around piece.
This hole is not so easy to clear out if blocked. You can try blowing air or running a fine wire up the telltale, but the passages in the block/manifold cover are easily plugged up over the years and short of disassembly probably can't be opened up.
You should be able to see, as the previous poster mentioned, water coming out of the back of the motor, at the exhaust relief ports. This is only when it's sitting in the water. If you're running on a flusher, most of the water will be discharged out the center of the exhaust tower and runs out the prop. You can tell it's circulating thru the motor if it's noticeably warmer than inlet water temp.
If you want to 'modernize' your Classic Merc, you can install a telltale. There's a stainless steel, slotted-head pipe plug at top aft port side of the engine block, just inboard of the exhaust manifold covers.
If you can remove this plug, it's a great place to tie in a telltale hose. Just use an angled fitting and run the hose to dishcharge out a hole that you drill in the lower cowling. You can pick up a later-model plastic telltale fitting, or just restrict the opening at the end of the hose to approx 1/8" thru use of a small diameter fuel fitting or similar.
Note that you may need to use a hand impact tool and heat from a propane or MAPP torch to 'persuade' the stainless plug to come loose.
If you're getting plenty of water up top, the exhaust manifold cover will be quite cool. Only should get warmed up after a long hard run but should never be so hot it's uncomfortable to touch.
The impeller advice is well-taken also, cheap insurance against toasting the powerhead! If you don't have personal knowledge of the impeller's condition, change it.
HTH.......ed
