Mercury 8.2l Horizon ECF Overtemp Alarm

[bfernald0]

I repowered in 2019 with 2 Mercury 8.2l Horizon big blocks. I flush them religiously. The boat's been sitting for a couple of months. Took it out to putt putt around the harbor for the annual holiday boat parade and had an overtemp alarm on the starboard engine. Vessel view showed the temp and coolant pressure were fine and identical to the port engine. Looking over the side, water flow was fine on both sides. Shut down the engine and restarted it to clear the alarm. 2 minutes later, same thing. Something also smelled hot.

Shut down the engine and went in. Next morning, an inspection revealed that the starboard manifold on the starboard engine had definitely gotten hot. The glossy black paint was now matte, and the exhaust temp sender wire that runs along the side of the manifold was melted.

Engines are 2 years old and have a 150 hours on them. Any thoughts?

 

[scoflaw]

Water pump or blockage. Manifolds/elbows replaced at same time ?

 

[paulswagelock]

Since the engine temps remained ok, it is the manifold temps that exceeded the threshold and set off the alarm. So, insufficient cooling water getting to the manifolds. Lots of potential causes. Plugged heat exchanger, plugged water passages, plugged riser/manifold waterway, partially blocked water inlet.

 

[bfernald0]

Since the engine temps remained ok, it is the manifold temps that exceeded the threshold and set off the alarm. So, insufficient cooling water getting to the manifolds. Lots of potential causes. Plugged heat exchanger, plugged water passages, plugged riser/manifold waterway, partially blocked water inlet.

Right, but only on one side. Very odd.

 

[paulswagelock]

Right, but only on one side. Very odd.

Not really. I had the 8.1 and had bravoitis and only the port side manifold would overheat. It is based on the water flow path.

 

[bfernald0]

I thought I'd post an update on this. Still dealing with it. The 8.2 liter ECT engines have poppet valves at the bottom of each exhaust manifold. The purpose of the valve I've learned is to keep water from draining out of the manifold at engine shut off. The valve is spring loaded and opens when the water pressure comes up to allow water into the manifold.

At idle, at the dock, both exhaust temps stay around 100 degrees. Under load, however, which means in gear puttering out of the dock, the port manifold starts rising almost immediately. It generates an overtemp alarm at about 233 degrees. The starboard manifold stays right at 100 degrees.

I replaced the port poppet valve, removed the riser, rinsed it out, and put everything back together. Same thing as soon as I leave the dock.

Talked to someone at Mercury and they advised that sometimes the poppet valve on the manifold opposite the one that's overheating sticks open, in which case the majority of the cooling water takes that path, depriving the opposite manifold of sufficient cooling water.

Going to swap out the starboard poppet valve on this engine, this weekend.

Very frustrating. Only 150 hours, flush the engines after just about every outing. Boats?!

 

[blaster]

You would think it is the poppet valve on the side overheating. Your answer makes sense though. This post will no doubt help people looking for answers with this problem. Emissions on boats are stupid to begin with. There are so few compared to cars.

 

[bfernald0]

That's what I thought, but replacing it did not fix the problem. The coffee can catalytic converters in each manifold get HOT too. The first time I got an overtemp alarm, I thought it was a bad sensor because the engine temp was fine... until I smelled the burning. Manifold got up to 335 degrees, at idle.

 

[juggernaut1]

I would also internally check the wet exhaust hoses on the problem motor. Mine internally blistered when I had a clamp fail and sea water hose blew off. Didn’t know until I changed out the manifolds years later. They don’t like being run without water for too long.

 

[bfernald0]

FIXED. Replaced the Poppet valve on the opposite manifold and sea trialed it. Exhaust temp on both sides stayed well within limits.

2 lessons here. Call Mercury. Their tech guys really have a wealth of knowledge and if you get one of the older ones that have been there for years (i talked to Mike this time) they are more than willing to talk the issue through.

Rinda scanner. Picked one of these up from Michigan Motors years ago for 600 bucks. Worth it's weight in gold. While i have all the vessel view data integrated, it's only a fraction of the available data-e.g., individual riser exhaust temps.

 

[Bob Miller]

Glad to find your post! I'm having exactly the same issues. On Port engine (8.2L Mercruiser) - overheat alarm. Engine temp is fine - the exhaust/risers appeared to be overheating.

Using a temperature laser gun, the port riser was around 190 and starboard riser around 120. Removed and cleaned the poppet valve on the port side. Didn't install a new one, just cleaned some sludge and rust out of it, put it back together and re-installed.

Today it seems the starboard riser is overheating while port stays ok. Going to do the same to the starboard side tomorrow, see what happens.

 

[bfernald0]

Glad to find your post! I'm having exactly the same issues. On Port engine (8.2L Mercruiser) - overheat alarm. Engine temp is fine - the exhaust/risers appeared to be overheating.

Using a temperature laser gun, the port riser was around 190 and starboard riser around 120. Removed and cleaned the poppet valve on the port side. Didn't install a new one, just cleaned some sludge and rust out of it, put it back together and re-installed.

Today it seems the starboard riser is overheating while port stays ok. Going to do the same to the starboard side tomorrow, see what happens.

I went through the ringer on this. My assumption is you've got the one catalyst on each side. The poppet valves at the bottom of each manifold actually have two valves in them--a springloaded valve on the side and a check ball valve in the plastic cup on the bottom (see attached diagram)

The springloaded valve is far easier to take apart because there are two bolts you remove and then pull the cap off. The plastic cup on the bottom that holds the check ball is press fit on. You can pry it off, but you need a shop vice to force it back on.

My advice is to do the following:

My assumption is that the water pressure is within range.

First, remove the exhaust temp sensor on the overheating manifold and run the engine (see diagram--its located on the back side of the riser). You want plenty of water flow coming out of that port (be careful as water will go everywhere when you're running). As a Mercury tech in Wisconsin explained to me on one of many telephone calls about this issue, if you don't have a solid flow of water (it's not high pressure by any means, but it's a decent flow), you've likely got a plugged manifold. Because of the size of the catalyst and the heat it generates, you've got a relatively narrow water passage running around it that is more prone to plugging over time. When you shut the engine off, the heat from the catalyst flashes any water in the water jacket to steam (the cats get up to over 2000 degrees), which results in the build of crap (sediment, salt and the like) on the water jacket innards. Additionally, if you're running in sand or mud, these manifolds are particularly prone to plugging due to the relatively small size of the water passages in the jacket. For theses reasons, it's particularly important to flush these engines after running. Even if you don't flush them, let them run for a few minutes before you shut them down. Such will help cool the catalyst before you shut it off.

Second, assuming you have plenty of water flow, get a set of pinch pliers (https://www.amazon.com/gp/product/B0743ZHQV8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1), and pinch off the hose coming off the BOTTOM of the poppet valve (Plastic cup), on the the side OPPOSITE of the overheating manifold. Then check the temp on the opposite manifold.

The two valves on the poppet valve assembly have different purposes. The check ball valve on the bottom of the poppet valve opens to allow the water to drain out when the engine is shut down. When the engine is running the water pressure closes the valve by forcing the check ball up into the ball seat. If this valve sticks open, the water will take the easiest path out, depriving the other side of the engine of cooling water. By clamping off the hose coming off the bottom of the poppet valve, you are simulating the check ball valve operation. If pinching off the hose causes the temp on the opposite manifold to equalize, it's a strong indication that the check valve is blocked open. You can pop the cup off the bottom of the poppet valve assembly with a screwdriver (it's on there pretty good), but you cannot get it back on without a vice. You can buy a new cup on Amazon for 7 bucks or so.

As an aside, the spring loaded valve on the side of the poppet valve assembly is intended to keep the overall pressure in the system up. It's rarely the cause of a differential heating problem.

If the results from the above are non-conclusive, let me know.

Good luck

B.

 

[bfernald0]

Actually, in thinking about this, you probably want to do the second task first as it doesn't involve taking anything apart ;-) In sticking with less work first, taking apart the poppet valve and cleaning it comes third.

 

[scoflaw]

have you ever thought of just deleting all that do nothing stuff off your motor which is prone to failure and just go back to old school
technology KISS ?

 

[bfernald0]

have you ever thought of just deleting all that do nothing stuff off your motor which is prone to failure and just go back to old school
technology KISS ?

Can't get away from it these days.

 

[Bob Miller]

Thanks for the detailed analysis! I appreciate the comments and tips.

When I had the poppet valve off on the port side, I could hear the check ball rattling around in the bottom before I put it back on. I ran water through it while cleaning the top portion, which had a bit of sludge (but like you mention, I didn't take off the bottom cup). I'm not sure if I noticed the ball rattling around before cleaning.

Early on in this process, I had already swapped the temp sensor from the port engine, starboard side with the temp sensor on the starboard engine (eliminating the the sensor from the problem). So, I'm going to remove the sensor as you suggest to check for water flow. If no water, then clamp off the bottom hose and try again. If I then get water flow, it would be a pretty good indicator that the poppet valve is the issue. If still no water, I've got bigger issues (manifold or riser blocked).

I do flush the engines *most times* after running. It's about a 15 minute ride at idle to slow speed from the ocean to the lift where she's kept. Most of it thru brackish water. So, that should help - but even after that I'll flush them out for 5-10 minutes once on the lift.

Port side poppet valve pictures below show the top portion - although cleaning the top chamber might not have fixed anything, maybe running water thru the entire value cleared something from the bottom. The starboard side might look the same - will let you know later today.

Thanks again for your comments.

 

[bfernald0]

Thanks for the detailed analysis! I appreciate the comments and tips.

When I had the poppet valve off on the port side, I could hear the check ball rattling around in the bottom before I put it back on. I ran water through it while cleaning the top portion, which had a bit of sludge (but like you mention, I didn't take off the bottom cup). I'm not sure if I noticed the ball rattling around before cleaning.

Early on in this process, I had already swapped the temp sensor from the port engine, starboard side with the temp sensor on the starboard engine (eliminating the the sensor from the problem). So, I'm going to remove the sensor as you suggest to check for water flow. If no water, then clamp off the bottom hose and try again. If I then get water flow, it would be a pretty good indicator that the poppet valve is the issue. If still no water, I've got bigger issues (manifold or riser blocked).

I do flush the engines *most times* after running. It's about a 15 minute ride at idle to slow speed from the ocean to the lift where she's kept. Most of it thru brackish water. So, that should help - but even after that I'll flush them out for 5-10 minutes once on the lift.

Port side poppet valve pictures below show the top portion - although cleaning the top chamber might not have fixed anything, maybe running water thru the entire value cleared something from the bottom. The starboard side might look the same - will let you know later today.
View attachment 129284

View attachment 129285


View attachment 129286


Thanks again for your comments.

If you can hear the check ball rattling around, it's probably fine.