Hi guys need some experienced input... Maybe I'm missing the obvious... I have a set of twins in my boat... One runs perfectly at 160, the other runs warm around 190-200... This all started when I had a water pump failure on the garden hose warm up, dewinterizing and flushing the rv antifreeze out of the open cooling system... The alarm went off and the motor got very warm like 210 degrees... Shut it off immediatly. I rebuilt the sea water pump on the side of the engine, still runs hot on garden hose, or in the river. Changed thermostat, no difference. took thermostat out and it will run below normal around 100 degrees. i assumed the worst so I pulled the heads and had them pressure checked.. No cracks.. they were out of plain .005".. had them plained and reinstalled them... None of the water jackets in the block nor the heads were plugged.. The gaskets showed no signs of any leaks or seepage. Reinstalled everything all new gaskets, even riser gaskets.. The damn thing still runs warm.. What am I missing? There is plenty of water flow out both exhaust ports... This engine has the newer style thermostat housings on it with the check valves... Here's something else I noticed.. There is two hot water returns and two cold water exits on top of the thermostat housing that go to the exhaust manifolds and to the risers? These are not plumbed the same on both sides... The right side has the cold water going to the manifold, and hot water going to the riser..... the left side is just opposite with the cold water to riser and hot water to manifold...... Doesn't this seem wrong? I searched everywhere with no luck on a full sea water cooling diagram ,, everything comes up for an MPI.. My serial number on my engine is OC 389263

Thanks

can you throw a bunch of pics of your set up cooling side

here is a SB about possible the problem and it does not have to be a saltwater boat either.

http://www.boatfix.com/merc/bullet/90/90_14.PDF


Did you change the water circ pump to new -

It really is not that hard to find cooling problems especially if you used clear hoses in place of the some of the rubber hoses for test purposes only.

Does exhaust manifolds and or risers have no restrictions or rust build up in the water jacket areas.

Does your t-stat housing have the T fitting with the spring loaded check balls in it ???

Mercruiser for 1989 on the big block OEM stock did not have an MPI engine. That came into play 1993 - FYI

I would check the inlet side of the oil and or power steering coolers.The rubber pieces will clog up there and will not pass thru the smaller holes in those oil coolers. good luck hf...

IMO says dealer stumped - I really would think they would know this already about impeller pieces blocking backside of the oil cooler and possible other areas. this is such common knowledge even for people who are not in the marine industry, If in fact that is your problem I would like to know who the dealer is hopefully not a John Deere tractor dealer here or the salemen. Just saying.

I have found pieces of the rubber impeller wedged into the thermostat housing passages. Use a piece of a coat hanger and work it through the different passages.

You sure the t-stat, t stat sleeve, and etc are installed correctly ? Sleeve is orientated coectly ? People screw this up all the time.


The check ball outlet hoses go to the risers,

http://www.mercruiserparts.com/image...R/19378/29.png

Thanks for the quick reply.. I will try to upload some pictures tonight.... The hoses are correct now only one was reversed. The cold water bypass does go to the risers so the exhaust is cool going through the fiber glass hull.... I did not change the engines circulating pump this go around since it was changed about 4 years ago when it started leaking out the weep hole.... All of the water jackets were clean on the risers and manifolds when I had it apart doing the head gaskets (which was un necessary) My T stat housings do have the spring loaded check balls and the balls & springs were replaced recently.. I'm just amazed this thing can get warm since the water I used is from a cold well at 45 degrees. Not rural city water... Half fast I also did what you said and checked the oil / power steering coolers, no restriction, even back flushed it. As for the dealer being stumped, I haven't taken it to one yet, This is all verbal in person communication... Honestly there's no one around here within 60 miles that works on boats except a small dealer down by where I work who mostly works on out boards, few in board sales , . SB i will double check the thermostat housing for the sleeve's correct installment but the way mine is made its notched and only goes in one way i'm pretty sure... I agree with all you when saying this problem should be an easy fix , these cooling systems are pretty simple.. I pulled the hose off coming from the sea water pump after the exchanger to verify good water flow on both engines for comparison and they are identical.... One thing i did notice is that when facing the port side engine the right manifold risers is ALOT hotter than the left... I don't understand why either as the their is no restrictions in the cold water by pass or riser inlets. The starboard engine has the same characteristics in regards to one manifold riser running warmer but its not much of a difference at all.. I'm guessing its because of the direction the water is coming in it naturally flows to the left easier than having to make a complete 180.... Do any of you guys believe when it warmed up on the initial pump failure that maybe rust or sand that was lodged in various places internally could have broken loose and now blocking something? The cylinder walls, pistons and water jackets all looked in excellent condition when the heads were off. The engine has zero blow by out the valve covers also. Do dealers have clear hose test kits that can be installed for testing purposes ?

I just went to home depot and bought all different size clear hoses & lengths but made sure the wall thickness was stout. Then I bought plastic adaptor barbs all different sizes for connections to adapt to the rubber hoses already on the engine so I just had to take off one side only for a few of them. I use them for all different brand engines, Indmar, Volvo, PCM, Ilmor - (Mastercraft) and of course all Mercruiser when needed so I had to buy a lot of sizes and extra hose clamps. I also double up hose clamp connection when using the clear hoses because I do not water a leak that can induce air into the cooling system giving me a false reading.

What you are looking for is a solid stream of water with no air bubbles in the clear hoses. Also advance the rpms in increments to see how well the water flow stream increases or decreases or puts air bubbles in the flowing stream. The section(s) were you find this taking place is the section of the cooling system that is having the problem. I have been doing this for 20 plus years. It is also taught in marine OEM schools and Volvo penta even had a video and work sheet about this form of testing. Just saying.

Also you have to watch out doing this on the water hose as it is not recommended because the water muffs induce air in the cooling already giving you a false problems & readings. It is highly recommended to do this form of testing in the water and deep enough clean water.