Problems with brand new Mercruiser 383 MPI

[Rogerdog23]

Update: Dealer gave everything a good look with the computer and things looked good including fuel pressure while running on the hose. Said the warmest they can get the engine is 151 degrees. I had the same experience out on the water and have a screenshot of my VesselView Mobile saying 149 degrees at WOT after the engine had been running at cruising speed for 45 minutes. Dealer thinks this could be an issue and it should be running around 170 degrees. If nothing else it’s a starting point and something we can try and see if it helps.
muc I didn’t quite follow what the dealer was saying but something about if the computer sees the temp is cold it might not let something or other happen with the the fuel (spray too much or not enough?). That mean anything to you?

Just wanted to keep folks posted on what I learned so far. Sounds like I’ll have to go do a water test this week and see if I gain anything...but for now I’m just happy that they were finally able to get it hooked up to the computer and hopefully on the road to getting it fixed.

Also, I’ll avoid the whole Cat debate but wanted to let folks know that my new engine doesn’t have Cats in case that is helpful for placing your bets on what the issue ends up being.

 

[tank1949]

Where did you get that from? I think he said the opposite...Not to mention that cars are infinitely more reliable than they used to be. Harder to fix and more expensive when they break, but my wife's last car went 120k miles with zero done to it outside of normal maintenance before she got rid of it because she wanted a new one...

She sounds like my wife. No doubt longevity has gone up. I remember when first throttle body trucks came out in the late 80s. No power at all. They were almost embarrassing. I'll stick with my MC TB V and carburetors in a boat. I can fix most of it, if it brakes down 100 miles off shore.

 

[Searay205]

Target temperature is 160F that is what the thermostat is. I believe above 140F it goes in warm mode. So i doubt that is the problem. Most engines in the 80 and 90's (marine) had 140F thermostat. That the magic temp where salt doesn't crystallize on your internal passages.

 

[muc]

Dealer is correct 170° thermostat should be in this engine.
Running cool will cause it to use too much fuel. But don't think it would be 25% more.

 

[Searay205]

wow 170F if in salt water closed cooling would be worth it. One thing i learned working on my Cobras is the thermostat wouldn't open until the set temperature but wouldn't fully close until 10 degrees below. sounds like he has a 160F in it and that why he is reading 150F. I could never get my engines to come up to temp with 180F thermostat had to go 195F. Then engine temp would be 185F they had massive cooling systems. I see that on my 5.0 mpi, except in summertime my engine temps usually 151 using my Rinda. Last week with water temp of 85F and air temp 95F mine was running 158F unless i kept it buried and then 161F.

In addition my PCM doesn't go into closed loop until temp above 140F, i wanted to put a cooler thermostat in since i do go in saltwater.

 

[Rogerdog23]

muc Thanks much. Dealer just called and work is complete. It is running around 165 degrees on the hose now. That’s up from 149 degrees that I saw during my last trip on the water after running for 45 mins. Besides some kind of fuel improvement, would you think I will see any meaningful performance improvement? Another 200 RPM or anything? Going slower and with less power than my 350 is eating at me. Can’t get to the boat until Friday for a test so place your bets!

Oh and as a small thank you for your help I asked Mercruiser what “TAM” stood for. Technical Account Manager.

Thanks again to everyone for the thoughts. Hopefully this does the trick. Will definitely report back end of week.

 

[Searay205]

My guess is whoever said fuel rail pressure was right. Fuel injectors fire on and off. They are designed to work within a fuel pressure range. If you have twice the fuel pressure then when the injector opens you will theoretically get twice the fuel in the cylinder. that is where your excess fuel is being burned.

 

[Rogerdog23]

Quick update but not a great test.

Got the boat today and did our usual run to a local island. Unfortunately we had an incredibly heavy load of stuff and I couldn’t get an apples to apples comparison. I don’t think it will end up being a night and day difference but will find out tomorrow for sure now that the boat is unloaded.

One interesting note: The engine temp on
my VesselView mobile ran at 160 degrees pretty much the entire trip. Was told it should be 170 to 185 depending on how hard it is working. Was working it really hard for a while and 160 was all I got.

more tomorrow but wanted to give a quick update as promised.

 

[QBhoy]

Sorry if you’ve covered it before, but was there an issue with the old engine that may now be having an effect on things ? Like overheating and possibly having melted flappers stuck down the exhaust or similar ?

 

[Rogerdog23]

Nope. Burnt valve. Great question though.

 

[alldodge]

Might be the sensor, check the thermostat housing with IR temp gun to compare

 

[Rogerdog23]

Thanks, AllDodge. So there’s a temp sensor in there somewhere? I don’t have my IR gun with me but perhaps I can get to a hardware store as they are pretty inexpensive if I remember correctly. Appreciate the idea thanks.

 

[alldodge]

Its on the thermostat housing

 

[muc]

It's possible they might have installed a 160° thermostat instead of the 170° that's called for. The 160° is much more common then the 170° and the 170° is out of stock until late June. Add to that your engine used the 170° up to serial number 1G700911 (so you can see your engine is very close to that serial number break) after that serial number, 160° was used on this engine. The part numbers for the ECM are the same for both the early and later engines so I would assume both have the same calibrations in them. So it's possible MerCruiser tech support gave the OK to use a 160° for a warranty repair on your engine.

If you still want to check. Your engine has 2 temp senders on the thermostat housing. The starboard side will have a one wire sender that is used for boats with analog gauges. The one on the port side will have two wires that feed the ECM data that it uses for fuel calculations, warning horn and digital (smartcraft) gauges. Take your readings near the base of the 2 wire sender.

 

[Rogerdog23]

Thanks, Muc. What type of readings am I looking for on the two wires? Temp with IR gun or voltage test? If I do have the 160 would that let the engine perform as it should or do I need the 170 for full performance?

 

[muc]

Nope. Burnt valve. Great question though.

Yes that is a great question that I assumed the installing dealer had addressed and corrected.
Was it more then one valve? And did anybody say the word "tulip"? Did they tell you why they thought it happened?
This is a very important question!

 

[Rogerdog23]

One valve. Happened because I was a moron. Out camping with the full family and heavily loaded. Checked oil and it was way low...or appeared to be because of how the boat was loaded. Filled til full which turned out to be way too much engine oil...you know how this story ends.

 

[muc]

Thanks, Muc. What type of readings am I looking for on the two wires? Temp with IR gun or voltage test? If I do have the 160 would that let the engine perform as it should or do I need the 170 for full performance?

I’m guessing alldodge is trying to confirm that the 160 your seeing on vesselview is what the engine is running at. Vesselview is reading the temp that the ECM is using for its fuel calculation. So it’s important that ECM temperature and engine are close to each other.

All engine components are built to design tolerance. So if a thermostat is designed to be 95% accurate, the 170 stat could be 162 to 178 and still be considered “good”. Same goes for the temperature sender. So what we look for is situation where one component is at one end of the range and the sensor that’s monitoring it is at the other end.

Generally speaking, the hotter a engine runs the more efficient it is. But this isn’t a big difference and usually only matters in racing and corporate fuel economy.

As long as your over 160 and below 175. And vesselview and actual temperature are close, I wouldn’t worry about it.

 

[muc]

One valve. Happened because I was a moron. Out camping with the full family and heavily loaded. Checked oil and it was way low...or appeared to be because of how the boat was loaded. Filled til full which turned out to be way too much engine oil...you know how this story ends.

This statement worries me. Too much oil is bad, but it rarely burns valves.

I’m concerned that your original engine failed due to tulip valves. This something that isn’t covered under warranty because it’s considered customer abuse.
This is a fairly common marine engine failure.
If you want to use your boat “heavily loaded” then it MUST be propped to reach rated RPMs.
Do you also use the boat to tow tubes or wakeboards?

 

[Rogerdog23]

I don’t do any towing and was able to get 5050 RPM on the old engine so was well within range. To clarify a bit it wasn’t that there was a ton of weight on the boat as much as it was all on the extended swim step to free up our limited deck space. So the attitude of the boat was not at all normal. What do tuliped valves do and could it have caused an issue that impacts the new engine?

Also, found the cut red wire. It has a purple stripe and goes to the round plug like on a boat trailer...I believe its called a 10 pin connector. It is in a black plastic conduit and is zip tied to take up extra length back near the round connector.