Help in solving an Overheating issue

[clinche]

I'll try and make this one as short as possible. I changed the engine of my maxum 2400SCR last month with a 5.7ltr V8 2BBL (yr 2000) raw water cooled..alpha 1 gen 2 leg..These are the symptoms with 2 adults onboard and full tank of gas and water..


Starts great
Idles to 160F - stat rated @ 160F
Planes well with tabs and drive down
Cruising @ 3600 revs for a long time - just under 175
Cruising @ 3800 revs for a long time - touches the 175 mark
Problems arise now..when i rev her up to 4K revs the temp starts creeping up very slowly however if i tilt the outdrive up (stil lleaving the lower drive completley immersed in sea water) the temp creeps up @ a higher rate..at a point where it reaches the mark after the 175 mark which i presume would be around 200F..alarm doesnt sound however i cant risk doing any damage so i lower the revs to 3800K and temp goes down to 175 in a matter of seconds...

Other things i noted was that last weekend the temp gauge freeked for a couple of seconds went down to 0 and back to 175 for 3 times and came back to normal again..My voltmetre is not reading the correct voltage of the batteries as well when i tested the batteries with an independant voltmetre...

Things i have changed and checked
Changed - Manifolds, Risers, Thermostat, Impeller, Spark Plugs, all filters and oils

Checked - Cooling hoses in engine compartment for leakages and for water pressure, compression good on all cyclinders, oil level good and clean..


Spoke to my mech and he is very confused..he will be connecting another set of gauges to bypass the current ones (thinks a bad earth or a bad earth in the lower drive which causes the temp to rise when the outdrive is tilted upwards)..should problem persist he will check the engine temp with an infrared temperature reader...Should the temp alarm sound if gauge needle is on the mark after the 175F mark??

Any suggestions guys on other things i can check..this is gettin kinda frustrating and expensive..

 

[Fun Times]

Re: Help in solving an Overheating issue

Hi, keep in mind your gauge or temp sending unit or wiring might be out of adjustment or have a bad connection some place and could be just reading hi as I have seen this in the past And there might not be nothing wrong with the engine it self. Or you might have a cloged up cooling system some place also. Have you ever burned up an impeller in the past, You might have some old rubber parts or dirt stuck some place in the cooling system, Like maybe one of the oil coolers or maybe the thermostat or in the intake water hose in the transom assy behind the bell housing going all the way up to the engine.You might also have a blocked exhaust some place. Also this tool in this link will be a grate help as you are looking for you engine temp problems.http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96451 Also keep in mind if you have used any kind of sealent to the thermostat gasket with the too little rivet metal rings in the gasket then you might also get a bad reading from the temp sending unit to the gauge because the sender will loose it's ground from the sealent and make the gauge read some times hi and some times low. Also you could have a bad "O" ring or cork type gasket in side the theremostat housing that helps kind holds the thermostat in place and seals it up so to speak. And also the thermostat housing it self could be bad. Also you might need to do a leak down test to the engine to make sure every thing is in working order inside the engine itself. http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=94190. Also have you installed anything new to the bottom of the boats hull in the path of the water flow to the sterndrive that could be making air bubbles or installed a new water pick up on the bottom of the boat? Also if you did a new impeller then some times the impeller housing/base in the lower unit might not be right, Also is the impeller after market or is it made by mercruiser? big differents there sometimes. Or maybe the water pick up tube inside the drive between the upper and lower housing is not sealed up right or in place right. Also keep in mind engines will over heat at around 3000 rpms if the the head gaskets are going bad. Also here is some good info out of a service manual on what to look for while trying to find out why your engine is getting hot. Well I hope some of this basic info will help you out while trying to find out why your engine is running hot, Good luck to you with it.

Engine Overheats (Mechanical)
Cause Special Information
Engine RPM below specifications at wideopen-
throttle (engine laboring)
Damaged or wrong propeller; growth on boat
bottom;false bottom full of water
Wrong ignition timing Timing too far advanced or retarded
Sticking distributor advance weights
Spark plug wires crossed (wrong firing order)
Lean fuel mixture Refer to ?Carburetor Malfunctions? in this section
Wrong heat range spark plugs
Exhaust restriction
Valve timing off Jumped timing chain, or improperly installed
Blown head gasket(s)
A blown head gasket(s) normally cannot be
detected by a compression check. Normally the
engine will run at normal temperature at low
RPM, but will overheat at speeds above 3000
RPM.

Engines that are seawater cooled

: Using a


clear plastic hose, look for air bubbles between


seawater pump and engine. If there are no

bubbles present, install clear plastic hose

between thermostat housing and manifold(s).If
air bubbles are present at a higher RPM, it is a
good indication there is a blown head gasket.
Insufficient lubrication to moving parts of engine Defective oil pump, plugged oil passage, low oil






level.


IMPORTANT:



The first step is to verify if the engine



is actually overheating or the temperature gauge or


sender is faulty

Loose or broken drive belt

IMPORTANT: Best way to test gauge or sender is
to replace them.
Seawater shutoff valve partially or fully closed
(if equipped)
Clogged or improperly installed sea strainer
Loose hose connections between seawater
pickup and seawater pump inlet (models with
belt driven seawater pump only)
Pump will suck air. Pump may fail to prime or will
force air bubbles into cooling system.
Seawater inlet hose kinked or collapsed
Seawater pickup clogged
Obstruction on boat bottom causing water
turbulence
Obstruction will be in front of seawater pickup,
causing air bubbles to be forced into cooling
system
Defective thermostat
Exhaust elbow water outlet holes plugged
Insufficient seawater pump operation Worn pump impeller
Obstruction in cooling system such as casting
flash, sand, rust, salt, etc.
Refer to water flow diagram for engine type
being serviced
Engine circulating pump defective
Also refer to ?Engine Overheats (Mechanical)?
IMPORTANT: In addition to previous checks,
make the following checks if engine is equipped
with closed cooling.
Low coolant level
Antifreeze not mixed properly Antifreeze should be mixed 50/50 or maximum
60/40 (60% antifreeze, 40% water)
Heat exchanger cores plugged
Water hoses reversed at the water distribution
block






Refer to water flow diagram in Section 6.
Insufficient Water Flow From Belt Driven Seawater Pump
Cause Special Information
Drive belt Loose, worn or broken
Seawater shutoff valve partially or fully closed
Clogged or improperly installed sea strainer
Loose hose connections between seawater pickup
and seawater pump inlet
Pump will suck air, pump may fail to prime or will
force air bubbles into cooling system
Seawater inlet hose kinked or plugged
Seawater pickup plugged
Obstruction on boat bottom causing water turbulence.
Obstruction will be in front of seawater pickup,
causing air bubbles to be forced into cooling
system

Faulty seawater pump

 

[clinche]

Re: Help in solving an Overheating issue

Thanks for the very useful information..looks like an elimination method would detect an overheating issue..i plan to work it out as follows:

bypass current gauges with another set
Read engine temp with the laser reader
Go through all hose pipes and confirm that they are all clean..and yes impeller had been changed because previous owner had burned his out..

is there a particular order on which hoses to remove first? i only found the water flow diagram in the manual...

i know this may sound stupid to some or all of you but i am finding it hard to understand the following causes in the manual.
"loose hose connections between seawater pickup and seawater pump inlet" - is the seawater pickup the impeller and the seawater pump inlet found in the transom? can you check this out with the drive in place and in water?

"sea water inlet hose kinked or collapsed" - where is this hose?

appreciate any help

 

[NoGin]

Re: Help in solving an Overheating issue

This should be a sticky! I am having the same issues except 175 plus degrees at around the 3500 mark. Seems like this is a common problem among boaters and gets very frustrating very quickly! My mechanic has been on board diagnosing this problem to the tune of 8 hours and $400!! Still having the same high temp reading....

 

[coastalcruiser]

Re: Help in solving an Overheating issue

NoGin This should be a sticky!

+1 excellent post

 

[dodgezilla04]

Re: Help in solving an Overheating issue

its not just the impeller that needs/should be changed. the wear plate also can cause the pump to have poor performance.

 

[bruceb58]

Re: Help in solving an Overheating issue

To answer one question, a lose hose clamp can allow air into the system.

A loose hose clamp is not going to be his problem. This is an alpha drive so the impeller is in the drive. Everything between the impeller and the engine will have a positive pressure so the only problem you would have with a loose hose clamp is some water coming out...not air going in.

 

[cr2k]

Re: Help in solving an Overheating issue

Melted impeller housing allowing water to blow out. Check housing for any signs of melted plastic top and bottom.

175 is no big deal if this is a true reading.

don't get the "earth" thing???

 

[bruceb58]

Re: Help in solving an Overheating issue

"Earth" is another term for electrical ground. Not sure why a mechanic things there is a ground problem with the drive.

 

[Don S]

Re: Help in solving an Overheating issue

He has a Gen II guys, no plastic pump housing to melt. But the Gen II's do have other problems that cause overheats in the 3000 rpm range. Have a read of this service bulletin.

http://www.boatfix.com/merc/Bullet/95/95_13.pdf

 

[QC]

Re: Help in solving an Overheating issue

earth = ground

Edit: Never mind . . . Service letter is better than my drivel . . .

I love that the Service letter pays 2 hours . . . Does Merc pay diagnostic time too?

 

[Fun Times]

Re: Help in solving an Overheating issue

is there a particular order on which hoses to remove first? i only found the water flow diagram in the manual... [I think you will see what hose to remove when you open some of the links I posted below].


loose hose connections between seawater pickup and seawater pump inlet" - ??? {Is the seawater pickup the impeller???] [YES] [And the seawater pump inlet hose is found in the transom assy??? {YES the first half of it is on the out side of the boat, Then you have a hose on the inside going to a oil cooler.] Can you check this out with the drive in place and in water??? [not really] With it in the water about all you can do is maybe blow a lot of air/water from the inside water hose back down to the drive in hopes to change a clogged area for a minute if you are lucky, But at the same time it is worth a shot, You never know. Also keeping in mind if this is where the problem really is.

"sea water inlet hose kinked or collapsed" - where is this hose?

appreciate any help[/QUOTE]Sorry about the sew water pump confushion, Your impeller is in the stern drive it's self and it pushes water all the way over to the engine, If you had a bravo style drive then the impeller would be mounted to the engine block some place and it would be sucking water all the way from the lower unit stern drive up to the engine mounted impeller housing. You have a water hose that starts where the stern drive it's self is mounted to the bell housing on the out side of the transom assy, Sometimes the old impeller rubber parts, sand, or a kinked hose, ect, Will clog up this hose, See nuber 15 in this link, http://www.mercruiserparts.com/Show...96/4.png&inbr=1942&bnbr=90&bdesc=BELL+HOUSING. Then the water will need to pass thru fitting number's 16,17,18, And for some reason one fitting is not showing up in this link, And that is where you would hook up the water hose number [11] on the inside of the boat. http://www.mercruiserparts.com/Show.../2.png&inbr=1942&bnbr=70&bdesc=GIMBAL+HOUSING. Then on the inside of the boat the water flow starts at number 11 in this link. http://www.mercruiserparts.com/Show...r=2697&bnbr=110&bdesc=Standard+Cooling+System. Well I hope this info helps you out a little bit more And I did not get you too . Good luck.

 

[NoGin]

Re: Help in solving an Overheating issue

In my case I had a mechanic install a new impeller and housing, gaskets and O ring in early July before launching the boat. My new mechanic says I may have a weak impeller or perhaps the other mechanic only changed the impeller and not the other items as he said. I do have the Gen 1 outdrives.

 

[clinche]

Re: Help in solving an Overheating issue

hey boat tech...i really do appreciate your detailed explanation and links..you got me going for a day i will keep you posted with any news..hoping to check these out tomorrow..thanks again mate

 

[clinche]

Re: Help in solving an Overheating issue

let me see if i got this correct...

the u joint bellow is used for the driveshaft and the exhaust bellows is where exhaust and water is discharged from the risers? these have nothing to do with water intake right?

the water hoses and connections in the bell housing can be inspected when the outdrive is out. However i can test whether a problem arises from the outdrive by removing the hose intake in the thermostat coming from the outdrive and checking the water discharge..should discharge approx 7ltrs in 15seconds right? if not the case i still can not elimate the hoses in the outdrive to be the problem as a restrction could be felt when engine is revved up and not at idle right?!

i really think there is a restriciton in the outdrive as the overheating speeds up when outdrive is tilted upwards...

 

[QC]

Re: Help in solving an Overheating issue

the u joint bellow is used for the driveshaft and the exhaust bellows is where exhaust and water is discharged from the risers? these have nothing to do with water intake right?

Right.

Why are you ignoring the Service Letter that Don posted?

 

[Thad]

Re: Help in solving an Overheating issue

Right.

Why are you ignoring the Service Letter that Don posted?

You can lead a horse to water...

 

[Don S]

Re: Help in solving an Overheating issue

I love that the Service letter pays 2 hours . . . Does Merc pay diagnostic time too?

That is what Merc pays the dealer if it's a warranty claim, and includes diagnostic time. May take 3 hours to do the job, but Merc will only pay the dealer 2 hours.

 

[QC]

Re: Help in solving an Overheating issue

Yup ^^^^^ that's what I was curious about. I can't see how you could do it in three with the water test included . . . plus you've got to pull the boat out.

 

[clinche]

Re: Help in solving an Overheating issue

Right.

Why are you ignoring the Service Letter that Don posted?

no no i did not ignore it. actually i am going to try it tomorrow.

Don - can u please tell me the diametre of the pipe so i can buy it before i head to the boat?

Thanks for your help...