Overheating after freshwater conversion

[Hornblower]

This post is long overdue and I’m sorely in need of the advice of my fellow Sea Ray owners. Sorry it’s a little long, but I want to be thorough.

Background:
SEP ’09 - Purchased ‘04 260 Sundancer 350Mag B3 with verified 15 hours on engine. Boat was used in salt water, but equipped with fresh water flush out.
SEP ’09 - Contacted Monitor Products for recommendation to freshwater cool above engine. Monitor recommended their MFH-5320-B (Block and Manifold cooling)
OCT ’09 – My mechanic installs the above kit.

After the conversion and running the boat in the cool November waters of Moriches Bay, NY the engine would tend to get hot after coming off of plane. Here’s an excerpt of an email I wrote Monitor Products Support at that time:

“I can run the boat all day at normal cruising speed approx 3600-3700 RPM and the engine will stay around 167 deg.

Here's the problem: If I come off plane and go to idle (600RPM) the temp will slowly rise above 195 deg (the overheat alarm goes off at 195 or 196 deg).

If I then give it some throttle with or without putting it into gear 1000-2000 RPM the temp drops into the mid 170's fairly quickly, and then I'm OK.

I repeated this cycle about 4 times today. Each time I got up on plane I ran at 165-167 DEG.

I can run it at idle all day and it won't overheat.”

This was Monitor’s reply:
“When you go from high RPM’s to low RPM’s you’ll always get a spike in the water temperature, because your pump flow rates go down with the RPM’s and it takes some time for the system to stabilize. If the spike is excessive you may have an obstruction somewhere in the raw water supply line, check the hoses leading to the heat exchanger especially at the oil cooler and fuel coolers if your engine has them.”

Around this time my mechanic:
- Checked over the entire installation, verifying each connection.
- Changed the raw water impeller (the old one came out with no missing pieces and was in generally good condition).
- Found and replace a broken stud on one of the Monitor fittings (We believe this was letting air into the freshwater side)

I at this point I also discovered:
- The Coolant was nearly 100% Extended Life Prestone. Not as efficient in moving heat as a 50/50 mixture.
- The engine was only flushed with fresh water prior to the heat exchanger installation.

The symptoms persisted but we winterized the boat and agreed to tackle it in the spring.

MAY ’10 – My mechanic flushes the engine again, this time he used baking soda to clean out the block and replaced the coolant with pre-diluted 50/50 Shell Rotella ELC

The problem persisted but I think it performed a little better, but as the bay water warmed in subsequent weeks the issue got increasingly worse. One week when the bay water reached the low 80’s the engines operating temperature at 3,500RPM would reach the high 180’s when on plane (3,600PRM), which is too hot for it to recover easily (at least in its current state), requiring me to slowly bring the RPMs down to cool off the engine to prevent the temp from spiking.

July ’10 – My Mechanic removes the 160 Deg thermostat.

No change except it takes a little longer to warm up.

After persisting with Monitor Products support they reached out to their engineer who said it sounded like too much coolant was passing through the bypass. So Monitor shipped me a brass reducer to install on the bypass side to restrict flow though the bypass and send more coolant through the exchanger.

AUG ’10 – My Mechanic puts back the thermostat and installs in the bypass reducer.

No change!

I called Monitor back, but I think they’re puzzled. I asked them to please deal with my mechanic directly, which I’m waiting for either for them to reach out to the other.

I’m a pretty patient person, but now I'm determined to have this resolved once and for all. I want to take the family on a couple of long weekends and cruise to Block Island, Greenport etc. before the season is over, but this issue makes that impossible. So I want to do anything I can to remedy this situation soon.

BTW, the engine has never come close to getting too hot when running at idle (600 RPM) to about 2,000 RPM even after running like that in gear for well over an hour.

To summarize: The engine runs a little too hot at higer RPMs (3,500 and up) particularly in warmer seawater. It will overheat if run it at higher RPMs like WOT (I don't do that). It doesn’t recover well when coming off of plane. In order to prevent an overheat situation I have to run the engine at a fast idle (2,000RPM) for around 30 sec to keep the temperature from spiking and exceeding the 195 deg threshold for the overheat alarm.

Any ideas as to what’s the problem?
Has anyone seen this symptom before, with or without a heat exchanger?
What do you think we should check next?

Thank you in advance for your help.:smt100

Sincerely,

 

[larrytbull]

have you checked your risers perhaps they are due for replacement

 

[Dave S]

The only thing you didn't clarify was in the month between the purchase of the boat and the installation of the system did you run the boat with only raw water cooling and was everything fine then?

 

[rcknecht]

How is your raw water pump impeller???

 

[J Levine]

How about adding a thru hull intake for the motor and bypassing the intake from the drive?

 

[SCORPIO]

How much pressure are you running in the system? Are all the block and manifold water passages clean? Is there any gelled coolant present in the heat exchanger? If there is any salt residue in the block, it will react with the AF and produce a gel like sludge that will clog the exchanger and cause heating.

 

[Hornblower]

Hey thank you for your quick replies.

Risers - I guess it's possible it's the risers as they are 6 years old, but the engine has only 50 hours on it now, and the problem started when the engine had only about 21 hours on it when the freshwater conversion was first put in. I'll mention it to my mechanic for sure.

Prior to conversion - We did put about 6 hours on the boat before the conversion. 2-3 on Lake Erie where I purchased the boat, and the remaining on Moriches Bay. I never watched the temperature gauge very close but the overheat alarm never went off (never reached 195 deg). I had a reputable marine surveyor look over the boat and take it for a sea trial it before I purchased the boat. He opened it up (WOT) too for a bit, no problems.

Raw Water Pump – That was the first thing we replaced (the impeller), and the old one looked fine.

Adding a thru hull – My mechanic mentioned he did this for another boat that had a similar issue. He determined that air was being picked up from the outdrive at high speeds and the thru hull took care of it.
He said that he wants to add a clear piece of 1.5” hose on the raw water side and look for air. I’m not sure that’s my issue as I’m not being cooled off very well at idle speeds too.

Pressure- Back in the fall post conversion I could cruise at 3,600 RPM and the engine temp would stay around 165 to 167 deg (salt water/raw water temp 55 deg), Water pressure 22.5 or so, Oil pressure 55.6 and running around 11.3 GPH. I don’t have notes on the pressure is at idle but I I’ll check it the next time we try to debug this problem.

Gelled antifreeze – We thought of that too, but this spring I had my mechanic flush the system again and he added Shell Rotella premixed antifreeze. The extended life Prestone that came out was fluid but a little brownish from fine rust particles.

 

[Sundancer]

I've never heard of baking soda being used to flush an engine? I've heard of using various acids to clear the salt from the block, but baking sode?? I'm not familiar with that and I'm wondering if that's a normal practice? Anyone else used baking soda?

I agree with Scorpio that the salt will react with the AF to cause a jello like substance that can create havoc in your block. That's why the acid is generally used to flush it all out.

Keep us posted! I'm sure Monitor will stand behind their products and maybe they need to increase the size of the heat exchanger?

 

[fc3]

Sounds like a lot of effort, time, and cost for nothing. Most gas engines wear out before they rust out. Take the system off, get a refund, go boating.

 

[Hornblower]

I've never heard of baking soda being used to flush an engine? I've heard of using various acids to clear the salt from the block, but baking sode?? I'm not familiar with that and I'm wondering if that's a normal practice? Anyone else used baking soda?

I agree with Scorpio that the salt will react with the AF to cause a jello like substance that can create havoc in your block. That's why the acid is generally used to flush it all out.

Keep us posted! I'm sure Monitor will stand behind their products and maybe they need to increase the size of the heat exchanger?

I never heard of Baking Soda either. It's certainly not going to hurt anything and it is a good general cleaner. I thought acid was for removing rust not salt.

I doesn't appear to be a gelling issue as the Prestone we flushed out in the spring looked fine (liquid no symptoms of gelling) and we replaced with fresh coolant and still had the same symptom (well before any gelling could occur if it was that)

Monitor tells me that it's the right size exchanger for the engine and they have sold many of these that are working fine with this engine.:huh:

 

[EricW]

My 2005 Mercruiser 4.3s with factory FWC use thru-hulls for the water intakes. The original RWC engines used the drives for the water intakes, and the thru-hulls were added when repowered with FWC engines.

I assume you already have the accessory belt-driven sea water pump? Pulling water from a thru-hull rather than the outdrive might be a good option.

 

[Hornblower]

My 2005 Mercruiser 4.3s with factory FWC use thru-hulls for the water intakes. The original RWC engines used the drives for the water intakes, and the thru-hulls were added when repowered with FWC engines.

I assume you already have the accessory belt-driven sea water pump? Pulling water from a thru-hull rather than the outdrive might be a good option.

I do have a belt driven raw water pump.
Why did they go with thru-hulls, do they perform better? Was it because of the FWC or the new engines?
I also like the idea of locating the pickup higher than the botton of the outdrive and having a screen. Moriches Bay is quite shallow and it's easy to churn up a little mud in many of the coves particulary, getting in or out of my marina at low tide.

 

[EricW]

I really don't know for sure why they added thru-hull water intakes when it was repowered. I bought the boat that way.

The previous engines were also 4.3s, just RWC. I have to assume that the thru-hulls were added due to the change to Closed-cooling.

The previous owner repowered with brand new complete 4.3 MPIs with closed cooling. I wonder if Mercruiser recommended thru-hull water intakes? I think the shop that did the work does a lot of repowering --- maybe they installed the thru-hulls due to past experience?

 

[Hornblower]

Thanks for your reply Eric. I'm sure the thru-hulls would work fine, but the Monitor heat exchanger is supposed to be able to operate with the raw water pump drawing from the lower unit too.

 

[Chris Dauth]

OK, I've been down this track, only difference is that my 383 has the Mercruiser heat exchanger.

Here is a posting I made a little while back.

Bravo III and 2's also have a issue where the sea water hose passes thru the outer transom plate. The hose gets crimped down from corrosion on the outside of the hose.

It is an easy check, just remove the 2 bolts that hold the plastic barbed hose fitting on the transom plate and see if the hose is not squashed down. The outter hose terminates just behind the plastic fitting.

A sure fix is to change to "thru the hull" cooling. Mercruiser make a kit to achieve this. Once done, you get a much better water flow.


And from the same thread,


OK, with the Merc Kit, there is not much to it. Just a metal plate and a gasket with a printed sheet of instructions.

Basically, all you need to do is remove the plastic hose fitting and place a solid gasket under it to blank off the hose, and then put the hose fitting back, tighten up the 2 bolts.

The most important part of this proceedure is to cut away a section of the hose between the transom plate and the top gear box. This allows water to be forced into the intake on the leg and up thru the water passages to cool the gear box. If you leave the hose intact and blanked off, you will have no cooling.

The next step is to install a bronze skin fitting, 1.25", designed as a scoop with a grate on the leading edge.

Inside the boat you'll need a ball valve, bronze with SS ball, and a hose fitting and a length of 1.25" hose that won't collapse under vacuum. The hose runs from the ball valve to the inlet of your raw water pump.

On top of the ball valve, I installed a "Tee" with a garden hose fitting so I can flush out the system with fresh water. To do that, you will need an extra ball valve.

Here is a picture when the motor was out, the skin fitting is on the starboard side just aft of the engine mount. You can see the yellow handle on the ball valve under the red starter cables.
The hose fitting for the engine is aft and forhead is the extra ball valve and the garden hose fitting.

The thread is here :- http://clubsearay.com/forum/showthread.php?p=379361#post379361

It is a fact that you will get a temperature spike when you throttle off. I have seen the 383 go to 200F, but never had an alarm. The "spikes" are not good for the motor, the thermal shock stresses the block. I is a common cause of failure in Volvo diesels.

I normally drop the engine down to about 2250 RPM for about a minute before I go on the hook, and the same before I enter the marina on the way home. The engine stays at about the normal 170F.

Hope this helps out.

.

 

[magster65]

I had the same problem (exactly) on my '06 240. It was the location of the temp sensors... here's a copy of the email I sent the manufacturer.
I installed the kit as per instructions and everything fit pretty well except for the drive oil relocation bracket had to be notched for the oil filter housing bolt (no big deal though).
It didn't warm up on the muffs like I expected, the temperature fluctuated a bit. I decided to take it out to see if it was ok in the water. It warmed up alright (kinda) so I left the dock and put it up on plane... with no problems. The temperature stayed normal. However, when I slowed down the high temp alarm went off so I shut it off, let it cool and putted back.
I took it home to troubleshoot after I couldn't get it to 'burp' or anything easy like that.
After some frustrating driveway testing I borrowed a infra-red 'gun' and found that it was the location of the 2 temp sensors (they're apparently very sensitive). The engine wasn't getting hot, just the brass 'T' and fittings in the kit were. The fittings made that 'tree' too tall and it caused the flow to stop just long enough to allow the sensors to read a false temp when the throttle was backed off. It acted like 'heat soak' mimicking like if you have too small of heat exchanger. To remedy this I made a new t-stat housing that puts the sensors back on the housing where Merc puts them. It was easy to make. I used the housing that comes in your kit and sliver-sautered a 90 degree elbow (with a sleeve inside) it right on top of it. It directly faces the exchanger tank inlet with about 1/8" clearance. Then I drilled two holes on a 22 1/2 degree angle (roughly... just off enough so the bolt can go in) and silver-sautered two 3/8" threadlettes for the sensors. The only other thing was to shorten the upper hose down to about 4" inches to cover the small gap instead of the angled hose in the kit. I painted it black and that was it... it looks right at home.
I just thought I'd send you this for your information and thanks again for the tour while we were there.

 

[Hornblower]

Chris Dauth thank you for your reply. It seems reasonable to assume that thru-hulls will provide a better less restricted flow of raw water. At this point I’m almost certain to do it too, even though I think it should work without this modification.

I will also have my mechanic check the hose at the transom plate.

As for the temperature spikes, I’ve been very careful to avoid them by slowly coming off of plane and keeping my eye on the temp gauge. But since the bay water warmed up the problem got much worse making it impossible to go for an extended cruise, and forget about running with the RPM’s over 3,600. I understand the temperature will naturally want to spike after you come off a plane, but not to this degree (no pun intended).

 

[Hornblower]

John aka Magster65, Did you install a Monitor Products Exchanger too? My temp sensors/senders were relocated to the Monitor Lower Heat Exchanger Bracket (See page 9 on their MFH-5320 Kit Instructions).

 

[Chris Dauth]

Did you get to see the picture FLcatsailor posted at ???

http://clubsearay.com/forum/attachment.php?attachmentid=11227&d=1281655302

One other bit of poor design is, there is no isolation valve between the transom plate and the inlet of the raw water pump. A friend who has a 280DA, had the hose pop off the inlet of the pump due to a rotten hose clip, almost sank the boat. It was a good thing he was still onboard and noticed the boat was much lower in the water as he was about to leave the marina !!!

BTW He also discovered the float switch on the auto bilge pump was not working, a wire had rotted off.

 

[Hornblower]

Did you get to see the picture FLcatsailor posted at ???

http://clubsearay.com/forum/attachment.php?attachmentid=11227&d=1281655302

One other bit of poor design is, there is no isolation valve between the transom plate and the inlet of the raw water pump. A friend who has a 280DA, had the hose pop off the inlet of the pump due to a rotten hose clip, almost sank the boat. It was a good thing he was still onboard and noticed the boat was much lower in the water as he was about to leave the marina !!!quote]

Chris, I did see it, impressive clog! My mechanic said he checked the flow from the raw water pump but I'm not sure if it was anymore than a quick visual. I think we'll take a look at this and maybe install thu-hull intakes too. At this point I'm certainly not adverse to spending a few extra bucks to improve the situation. I hope to catch my mechanic in the morning to discuss a new plan of action. I'll keep you posted.