Extremely Hot Tell Tale

[Gill Reaper]

Serial #OT149266

I have a 2000 Merc 200 carb motor that is overheating at higher rpms (4500+ rpms). Water coming out the tell-tale is extremely hot. The water is hot as soon as you start the motor. I'm thinking exhaust gas is somehow mixing with the cooling water. Could a bad powerhead gasket or bad midsection gasket cause this problem?? Motor starts and idles fine. I can run it all day with lower rpms. Mechanic said compression is good and no scarring on the cylinders. Had the water pump, thermostats, and poppet valve replaced. Temp gauge shows 180 degrees. When I come off plane the alarm goes away. Any thought?

[JOE54]

yes they sure can cause this, what is water psi at 5000-5500

[Gill Reaper]

Not sure because I don't have a gauge installed. I will get the mechanic to hook up a gauge to see,

[EuropeanAM]

Moving your post to the 2.5L (correct) Forum.

Your engine's telltale comes from the thermostats. There may be little, or no telltale, until (or unless) the thermostats are OPEN, and when it is present, it will be SCALDING HOT (as in 140-155 degree range). KEEP HANDS AND BODY PARTS OUT.

What method have you used to determine the engine is overheating? Warning Horn?

[Gill Reaper]

Horn comes on, constant beep. I've run it with and without thermostats, still get the same result. Water is so hot you can't hold your hand in it more than 10 seconds. Boat and outboard ran well for over 5 months when I purchased them and then all of a sudden, this problem popped up.

[leonreno]

10 seconds is longer than I would hold my hand under mine. Is the beep a Beeeeeeeeeeeeeeeeeep or constant beeps like beep beep beep…? Since a new purchase to you at 5 months and if you don’t know when the pump was changed before that, it’s time to change the water pump, always start at the source as has been for-told by Don many times.. water pumps are to be changed year or 100 hours, which ever comes first.

[Gill Reaper]

Water pump, thermostats, and poppet valve have been replaced with no change. It's a constant beep when it overheats. If I come off plane and idle it will stop. I've owned this boat for over a year. It ran good with no issues for the first 5 months. I've been chasing this overheating problem every since then. I've had a couple mechanics look at it and they couldn't figure it out.

[lpugh]

bad head gasket, compression and leak down test in order, during leak down test have thermostats removed and listen for air leakage from the openings in the cyl head

[EuropeanAM]

Let's back up a minute. Go back to the WATER PUMP. Pull it back down, carefully disassemble and VERIFY that fins are in correct fold orientation for CLOCKWISE shaft rotation, and VISUALLY inspect all three gaskets (suggest pictures).

This engine will not cool properly without thermostats.

Once all above are done, PULL THE POPPET VALVE and inspect for problems. Good idea to have a kit on hand.

One of the gaskets has a bad habit of "pooching" into the water passage, restricting it. You'll probably easily tell this once you look at it. My preference is to CAREFULLY trim the cork gasket along that passage and remove the part of the gasket that offends in this way. Reassemble with (at least) a new grommet, poppet, gaskets, diaphragm and spring.

THEN see if you continue to have problems before you get deep into tearing things apart.

[Gill Reaper]

I have a mechanic looking into it now. He has already replaced the thermostats and installed a water pump kit with no change. Previous mechanic installed a new poppet valve kit with no difference. Head gaskets were also changed out about 6 months ago and no difference.

[EuropeanAM]

Gotcha. The only thing I can tell you is that if I had a quarter for every time I pulled a "new" water pump or poppet valve only to find the problems I've mentioned above, I could easily plan a nice little stay for the family on a long weekend (at a minimum).

[Gill Reaper]

Gonna send this message over to the mechanic thats working on the boat. I'll update when he makes some progress, thanks for the help!

[lpugh]

Serial #OT149266

I have a 2000 Merc 200 carb motor that is overheating at higher rpms (4500+ rpms). Water coming out the tell-tale is extremely hot. The water is hot as soon as you start the motor. I'm thinking exhaust gas is somehow mixing with the cooling water. Could a bad powerhead gasket or bad midsection gasket cause this problem?? Motor starts and idles fine. I can run it all day with lower rpms. Mechanic said compression is good and no scarring on the cylinders. Had the water pump, thermostats, and poppet valve replaced. Temp gauge shows 180 degrees. When I come off plane the alarm goes away. Any thought?

This is why I believe it is a bad head gasket, seen this a few times. This is the only way you would have pressure and instant hot water.

[JOE54]

This is why I believe it is a bad head gasket, seen this a few times. This is the only way you would have pressure and instant hot water.

could be oring mtr also yep yep could be

[leonreno]

Does the water come out of the tell tale immediately even with the thermostats installed?

[Gill Reaper]

Head gaskets were changed already, water does not come immediately with thermostats installed.

[lpugh]

Head gaskets were changed already, water does not come immediately with thermostats installed.

Do it anyway, Post #8, got to sure there are no combustion leaks!
Inspect the block area that retains the sleeves for splitting especially if using 0-rings

[EuropeanAM]

Head gaskets were changed already, water does not come immediately with thermostats installed.

Gill:

Let's find something out here before you tear into this thing. You stated that water does not come immediately with thermostats installed.

If it's taking 60-180 seconds before you get water at the telltale, and the water at that point is HOT, that may very well be PERFECTLY NORMAL for this model!

Let's get very clear information on this, preferably you actually time how long it is before hot water is present at the telltale, before going any further.

Also: If you can test this on a set of MUFFS, check the temperature of the water coming from the center of the prop. THIS is the exit point for 90% of the cooling water, and it would normally be considerably cooler than the telltale. If so, and there is still question of head gaskets, see below:

There is a specific and simple test to check for compression leakage into the exhaust, it does NOT require that the heads be removed. Simply install a clear piece of tubing onto the fitting/port just behind the flywheel (at the top of the block) and route that clear tubing in a 1' diameter "loop" at or above the powerhead. If there is a head gasket leak, you will almost certainly see BUBBLES (fast-moving, foaming and pulsing) in the clear tubing.

[Gill Reaper]

Shop is replacing the poppet valve in hopes it will solve the problem, I'll keep yall updated.

[massbays]

I would be load testing motor at a ramp on trailer with water intakes deep in the water.