350 Mag MPi overheating

[Last Tango]

2005 series 350 Mag MPi with Bravo One drive, 191 hours, factory stock.

No prior overheats that could not be traced to either a plastic bag floating in the water, or a temporary and minor influx of mud in shallow water. All cleared long ago. No overtemps in the past two years.

A couple outings ago the boat showed a slight tendency to run up a few degrees when coming off of plane. However, it would come down to normal within a few minutes of idling. Then the last time out, it ran hotter and hotter right from the beginning. The digital temp gauge showed 184 while at 3300 rpm's. Normally it stays right at 159 degrees once it warms up. When I came off plane and slowed down, the alarm went off and the digital temp briefly read 224. The analog gauge quickly pegged. Fortunately, I was back at my dock when that happened.

So, a very competent mechanic looked it over and we agreed that it could be either the thermostat, the impeller, or the curvy hose that chokes up inside Bravo Ones. So he replaced all three. He ran it on the hose and water came out of all the right places while idling, and he didn't think it was running too hot. He did put in a 170 deg thermostat and he stated that it stayed within that range. The old impeller was worn only slightly from normal use. No missing blades or chunks. Thermostat looked normal for 5 years in brakish water. The hose in the drive was extremely constricted from the outside from the expected 5 years of corrosion build-up on the outside of the hose that eventually crushes them down. I was told by several sources that this is a common problem.

No oil in the water. No water in the oil. Oil did not seem too hot, even with the overtemp readings. Full synthetic Mercury spec oil. Only 12 hours since that was last changed with the filter.
Brand new drive belt at that same time as oil change. Belt turning, all aux items rotating, no funny noises, engine does not smell hot or even feel particularly hot. No hot engine clicking sounds or boiling water sounds. no smoke or odors of any kind. Engine compartment temp normal.

So, I put it back in the water and off I went for a test ride. It began to overheat immediately. The digital temp gauge went up at a pretty consistent rate, and I turned back to the dock after only 5 minutes running. Digital temp got to 184 as I was coming off plane. Alarm went off, and the analog temp gauge pegged. At the the dock at idle, no water coming out of the through hull tips.

Back on the hose and up on the stand, the water came through all the right places, although the tips seemed a bit weak to me. But that could have been the angle of the boat on the stand. I have the permanently open Y-style Quick 'n' Quiet exhaust. No Captains Choice switch. Water always comes through both the tips and the exhaust port on the drive. Water was running freely from the outdrive port. Engine temp began to rise well through the 170 thermostat to 175 and I cut it off. Water coming out of the tips was only luke warm to the touch.

So water can be pushed through the system under pressure, but it won't do it on its own.

Water pump in the drive?
Water pump housing in the engine?
Thermostat housing blocked?
Exhaust Manifolds?
Heads?

I did lots of searches here before posting. Looks like it could be a number of (expensive) things at this point.

What say you?

(P.S. I have to be very careful what I wish for because it often comes true. In this case I have been waiting impatiently for 5 years for the risers and exhaust manifolds to clog up so I could order a new stainless steel EMI Thunder exhaust manifold and riser package. Did my Genie come through for me right on schedule?)

[Ranman]

Probably not the case based on your thorough description, but I thought I would chime in.

On my 97 MAG 350 Bravo I, the water pump with the impeller is plastic and has never given me an ounce of trouble. I change the impeller from time to time and this is a trailer boat that only gets launched at ramps. It always pumps without issue. I do always check the pipes at startup to make sure water is pumping before I leave the dock.

My Formula, with two 2004 350 MAG Bravo III's have brass water pumps and each pump has two blue "drain" plugs. This boat is launched each year with slings. Several times now, I've had it running on land via the hose and muffs for spring recommissioning and when it gets droped in at launch an air pocket prevents the pumps from getting primed with water and I get a pretty quick overheat condition. I've since learned to pull the lower blue plugs to purge the air and get water up to the impeller. Upon firing off the engines I pull the top plugs to make sure they're pumping pressure.

The first time before I knew what to look for / do (purge the air), I very quickly lost two impellers and had to learn to change them out while the boat was in the water since it's $100 to have it pulled and relaunched

Anyway, I hust thought I would throw this out there..

[MOP]

My vote check the risers they could be getting plugged which would not flow enough water for higher speed, worth checking, it is normal for raw cooled engine to show a temperature rise when coming of plane only to cool down as you describe. I have had to deal with that issue many times with new customers, even having to go for a ride or two to demonstrate it.

Phil

[fogducker III]

Just a thought, how do you flush the motor when on land? Is there a through hull fitting to attach the garden hose or "muffs"?

If it is a through hull, check the cap and washer that block it off at the hull as well as the line that feeds the water pump. On one occasion I left the cap off and the pump pulled air rather then water through, easier to pull air then water, motor heated up REAL quick.....yours seems to take a little time to over heat so perhaps there is a "small" air leak.......

Failing that it might be old impeller pieces in the lines?

[Morgan's Cloud]

, , . The hose in the drive was extremely constricted from the outside from the expected 5 years of corrosion build-up on the outside of the hose that eventually crushes them down. I was told by several sources that this is a common problem.

Are you confirming that the grommet in the trans plate that transfers water from the outside hose to the inside hose is OK ?

In your case this sounds like a classic example of it.

[Last Tango]

Foggy,
No through-hull fitting for the land flush. The earmuffs (and a special nose plug) fit over the bottom of the drive above the skeg and torpedo. There are a vertical series of intake holes on each side of the lower drive unit sort of like gills on a fish. The muff covers those holes and the hose connects to the muff. The nose plug blocks water from just pouring out a hole on the leading edge of the torpedo. All of the holes feed the same "plenum" area in the lower drive unit for the water pick-up. The nose cone hole provides a "ram air" effect for water to enter the drive when under way.

MC,
Since I was not present when the hose in the outdrive was replaced, I cannot confirm if the grommet was plugged, replaced, or even inspected. However, since the drive was removed to replace the internal hose, I would hope the mechanic inspected that since the whole reason for going in in the first place was to search for blockages.

MOP,
I usually experience a few degress of temp increase when first coming off of plane. But the recent activity far exceeded any normal observations. I do know it takes the cooling system a few minutes to cool the block down after running on plane and then reducing the amount of water flow when coming down to idle. But that increse was usually only a few degrees for a few minutes (amazing how persnicketty I can be about those details since I installed the SmartCraft System Monitor a few years ago. Analog gauges just don't provide that level of detail).


The mechanic has not had an opportunity to get back to my boat, yet. (it has only been a one actual work day since the test drive) Probably go in again this coming week. And I will be available to be there to ask questions (LOL! JUST what he wants! LOL!)

[Carbo]

I am assuming he replaced the "s" hose so that means he cleared both ends...they do the same thing. Problem is the motor end is a PITA to get to on some boats.

If he just shortened the hose to repair the bell housing side then your problem is probably the other end at the motor.

Any air leak on the intake hose/fittings/transom nipple will cause an overheat.

Surge temp when pulled back is normal as previously said.

[Last Tango]

So here is what we know so far:
RANMAN gets an A+ for his suggestion about checking the blue drain plugs. And everyone else had great ideas that seemed in some fashion to also be part of the problem. Most likely it was an air leak, perhaps in more than one place.
The previous mechanic sort of walked away on the project a couple months ago, and left the motor partially disassembled. So after waiting patiently for his return, I was fortuitously given a referral to an different mechanic through a most unlikely source (the guy who services our community water and sewage system knew a guy...LOL!) So this guy comes out promptly, surveys the motor and disassembled parts and begins to dig in. 3 hours later, he has completely removed and inspected and reattached every hose, fitting, and attachment on the motor and drive and put them all neatly and tightly back together. He says the first guy appears to have actually done the thermostat replacement, although with one that is 10 deg too high. He also says he is taking the risers home with him to clean up the mating surfaces with a grinder before reapplying the new gaskets that he will put there. The risers are completely clear as are the manifolds. No blockage of any kind and he says they look perfectly good for years to come. So he takes the risers home for the weekend to prep them for installation.
Monday he is back with all the right stuff, completes the reassembly in about an hour, takes a lunch break to let the gaskets dry, comes back and fires up the motor. He makes adjustments to all the controls, zeros out the trim gauge on the drive, and we watch the motor warm up.
It is on the hose with earmuffs and nose fob.
It starts to over heat again.
Water is flowing through the system, the risers stay cool, no hot engine parts or smells, but the actual flow out the exhaust tips is weak compared to my previous experiences on the hose in the yard.
We shut down the motor.
He climbs in and notices water dripping slowly from the lower blue drain plug. He tightens it up again. We switch from the hose to a deep bucket of water under the drive to ensure the motor and drive are sucking water on their own without being pressure fed by a hose. Yes, techincally we changed two things at once so that sullies the scientific method of troubleshooting, but we do it anyway.
Boat fires right up, water starts sucking through the drive and motor and out the exhaust tips at the normal rate of flow, and the engine warms up BUT DOES NOT OVERHEAT! TA-DAHHHHHHH! Probably was an air pocket, and probably from more than one point of origin.
He is going to replace the thermostat back to the correct 160 deg vs the 170 deg part the previous mech put in. Then we are going to give it the ultimate litmus test by lauching, with him along for the ride just to make sure.
I'll report back here when we have completed the test ride.

[VetteLT193]

The new blue drain thing is nice in winter but seems very sensitive. My engines have always run a bit on the warm side, upwards of 180 on the analog gauges.

Well, I developed a small drip on the port engine at that lower blue drain and now that engine runs 10 degrees cooler.

I'm wondering if I should try Ranman's idea this weekend... purge the water while in the water on the Starboard side to see if that one drops.

On a side note I developed a habit many years ago of slowing down well short of the slow speed zones and keeping the engine(s) up to 1200 rpm or so for a bit, then dropping to 1000, then dropping all the way down. it seems to really help the temp flux as well as oil PSI flux.

Also... I noticed my oil pressure stays roughly 10 psi higher after going to the Mobil 1 double sized filters this season. They used to drop to 20 psi after a run, now they stay around 30 psi.

[Last Tango]

I agree with you. Since my first powerboat many years ago (Classic 16, then Classic 18, then Z3250, then this 22ZX) I learned right away to always ease down on the throttles when coming off plane and going to idle, in order to minimize the rise in heat or lack of water flow when the block is still hot from running. Exactly like a race car ar the track - take a cool down lap after running hard so as not to overheat anything. I always ease the speed down slowly, and then try to keep the idle revs at about 900-1200 when still underway. I very rarely let the engine idle at 650-ish. Just not enough water flow in my opinion. Even on the trailer when flushing the system I usually run the engine at about 1300-1500.


And Ranman's suggestion is good. I believe we accidentally did just that after the mech saw the drip from the blue drain plug, because the water was still running into the engine from the hose (just like sitting in the water) when he readjusted the plug.

My analog gauge normally reads just a needle-width under 180 deg under normal cruising conditions. The digital gauge reads 159 deg normally. I attribute that to three possible things - all of which could be happening:
(1) Accuracy of the analog gauge, including it's small size (therefore lack of good detail), and paralax error (reading the gauge from different angles).
(2) Different locations on the engine for the temperature sensors for each type of water temperature gauge. Analog is up near the thermostat - digital is somewhere else internal.
(3) Basic accuracy of the analog gauge to begin with. I consider all analog gauge readouts to be "suggestions" rather than facts. My analog tachometer reads a couple hunder RPM higher than the digital tach in the SmartCraft display. Which would correllate with all analog gauges. Analog speedo's "always" read whatever that want - high/low/not-at-all, compared to GPS speedo's or RADAR gun.



Off Topic: I consider RADAR guns to be less accurate than GPS readouts because the RADAR gun reflects off the surface of the water for its info. That requires at least some ripples to get the reflection. Ripples and waves are driven by the prevailing wind which adds a speed vector that the RADAR gun does not calculate out. And if the reading is taken on a lake filled with wakes or crossing wakes, then it has all of that to deal with, as well, and it does not. GPS is a pure speed over the bottom reading, not speed through the water which is what an analog gauge reads - the biggest factor being current on the river or lake. Analog is great for speed through the water but is not an accurate system since it does not factor for water temperature or density and relies solely on the water pressure coming into the pick-up tube. And analog gauges rarely have the depth of detail available from GPS or RADAR - thus not the best instrument when doing prop testing and such.

[Last Tango]

So the mechanic took home the "old" thermostat, and plunked it in the water with the new thermostat that he ordered. The new one opened right spot on at 160 as advertised. The "old" themostat started to open at 170-ish but never fully opened


He installed the new thermostat and we ran it on the trailer for over half an hour. Both temperature gauges recorded perfect warm-up and temperatures at all running RPM's. Excellent water flow in and out.


So we will still do an actual sea trial in a few days, but it looks like we have resolved the issues.


To review the solutions: obviously the thermostat, and also the blue drain plug seems to have been the problems.

[Phil S]

Was hoping I was about to hear, "your wish is hereby granted ! "

"Problem solved"...is equally nice to hear though. Thanks for the feedback on the solution.

WKR,

Phil S.

[Last Tango]

Zoltan did in fact grant the wish I prayed the hardest for... and that was that the Repair Bill would NOT be BIG. LOL!

[Last Tango]

So today we finally got the chance to do the sea trial.

Problem with overheating is still as bad as ever.

Naturally I am disappointed since we had such a good trailer run a few weeks ago.

Mech was in the boat with me and saw clearly what happens. Now he is going to remove, inspect, and replace as necessary two flow valves in the lower part of the motor. The motor was too hot to try that today, so he is coming back tomorrow afternoon. Perhaps, if the clear weather holds, we'll get another sea trial late tomorrow evening.

Water is flowing well from the drive to the motor and out the tail pipes.
There is plenty of water pressure showing at all speeds.
The risers are relatively cool to the touch, even after running.
But the block heats up as though the water is not flowing through it.

I'll update you when we run the boat again.

[MOP]

Ask you mech to install clear hoses in place if the riser feeds, run it up and watch for a stream of air. If you see air even the tiniest amount it indicates either air entering the intake water flow or a head gasket leak, that is an old very simple test to check for that condition without tearing into it. If you have air entering the system it ends up filling cylinder heads allowing the block to heat up while everything else stays cool. I have seen something as simple as a loose hose clamp on the intake side of a sea pump cause a condition like you have. Another test is to use a heat gun check the heads and low on the block there should only be about 15 degrees difference, with the top being hotter any major variation means the air is forcing the water out of the heads!