help diagnosing overheat at idle

[the_dude]

So about a month or two ago I took my boat into the dealer for an unrelated problem.

When I got it back I took it out on a test run and everything was great until I got back to the dock and was sitting there idling. Saw the temps rising and reved up the motor and they dropped down. Did this a few times to make sure it wasn't a fluke. Figured the dealer must of run the engine to aggressively on the hose and put in a new impeller.

Two weekends ago I took the boat out again and it had the exact same symptoms. I plan on checking the tranny screen tomorrow (2 impeller changes I've done since owning the boat have never had any visable dmg to the impeller).

Given that the temp is rock steady at anything much over 1200 rpms I'm having a hard time believing it's the thermostat. Anything else it could be?

[tvano]

checking the trans cooler is the right first step.

if that does not pan out i would head back to the impeller, again.

although you have checked it, twice, you don't really know if the dealer ship gives a rip or if they ran it dry.

[Sixball]

I also would checking the trans cooler is the right first step. my ski buddy's boat started overheating at slow or idle speeds last year. I pulled the impeller and all looked good so I reversed the impeller and it ran just fine. I think the impeller took a shape and was not pumping to it full extent. We did put a new impelled in as soon as he could get one and kept the old one for emergency. I know my last two inboards would run fine at speed with a bad impeller. The boat speed was enough to force water through the system. I would not do it if it is not a emergency but it works it worked on my Budd's boat after blowing a impeller we pulled the bad one and put it on plane got home and on the lift no problem. The boat ran right at 180 deg.

[the_dude]

Thanks guys, love this site.

Just to be clear. I changed the impeller as soon as this symptom showed when I got it back from the dealer. With a brand new impeller it did it again.

The part about the two impellers was not inspecting but actually replacement. The impeller that was in it when it went to the dealer was 6 months old too.

EDIT: oh yeah, forgot to mention that if I bump up the revs a bit in neutral the boat still cools fine. I don't have to be moving or on plane or anything but no wake zones aren't too friendly right now :P

Edited March 28, 2009 by the_dude

[FFCole411]

Did you ever get this problem figured out? I am having a similiar problem. When I go 5-10MPH my needle on the temperature gauge is in the middle of the gauge. When I go roughly 25MPH or faster the needle on the temperature gauge comes down to stone cold. When I slow down to 5-10MPH the needle comes back up to about half way on the gauge. I do not have a temp. reading on the gauge so I do not know the exact temperature it is going to when going slow. It is not overheating though. If you have any insight on this problem I would appreciate it.

Thanks,

Cole

[rinconking]

try backflushing the water intake hose at the sea pump. you may have a clog in the pickup

[pup]

My friends nautique has a strainer mounted high on the engine. Between the thru hull fitting & the pump. The oring wasn't sealing properly. At idle speed the pump would pull air & the engine would heat up. Higher engine speeds the pump could get past the leak & move enough water so the temp was fine. If you have a strainer set up like this it's one more thing to check.

[the_dude]

Did you ever get this problem figured out? I am having a similiar problem. When I go 5-10MPH my needle on the temperature gauge is in the middle of the gauge. When I go roughly 25MPH or faster the needle on the temperature gauge comes down to stone cold. When I slow down to 5-10MPH the needle comes back up to about half way on the gauge. I do not have a temp. reading on the gauge so I do not know the exact temperature it is going to when going slow. It is not overheating though. If you have any insight on this problem I would appreciate it.

Thanks,

Cole

Hey Cole,

Nope never figured it out. I also haven't been able to get the trans cooler hose off to check it for obstructions. I have backflushed the vdrive unit and the hose to the impeller is clear I'm sure.

I am planning on swapping the motor soon and will inspect everything then.

I did take the boat out two more times after this post. 1st time the problem was very minimal. It took a long time to start to heat up at idle and any forward throttle at all and no problems. 2nd time old symptoms came back. It was odd that there was a change in the symptoms.

[electricjohn]

+1, the slightest air leak will cause your problem, even if you don't have a sea strainer.

edit; The problem will be more apparent as the engine room heats up.

Edited April 14, 2009 by electricjohn

[eyepeeler]

Did you ever get this problem figured out? I am having a similiar problem. When I go 5-10MPH my needle on the temperature gauge is in the middle of the gauge. When I go roughly 25MPH or faster the needle on the temperature gauge comes down to stone cold. When I slow down to 5-10MPH the needle comes back up to about half way on the gauge. I do not have a temp. reading on the gauge so I do not know the exact temperature it is going to when going slow. It is not overheating though. If you have any insight on this problem I would appreciate it.

Thanks,

Cole

Hey Cole,

Nope never figured it out. I also haven't been able to get the trans cooler hose off to check it for obstructions. I have backflushed the vdrive unit and the hose to the impeller is clear I'm sure.

I am planning on swapping the motor soon and will inspect everything then.

I did take the boat out two more times after this post. 1st time the problem was very minimal. It took a long time to start to heat up at idle and any forward throttle at all and no problems. 2nd time old symptoms came back. It was odd that there was a change in the symptoms.

Why can't you get your tranny fluid hose off?

[BlastRlxi]

Did you ever get this problem figured out? I am having a similiar problem. When I go 5-10MPH my needle on the temperature gauge is in the middle of the gauge. When I go roughly 25MPH or faster the needle on the temperature gauge comes down to stone cold. When I slow down to 5-10MPH the needle comes back up to about half way on the gauge. I do not have a temp. reading on the gauge so I do not know the exact temperature it is going to when going slow. It is not overheating though. If you have any insight on this problem I would appreciate it.

Thanks,

Cole

Hey Cole,

Nope never figured it out. I also haven't been able to get the trans cooler hose off to check it for obstructions. I have backflushed the vdrive unit and the hose to the impeller is clear I'm sure.

I am planning on swapping the motor soon and will inspect everything then.

I did take the boat out two more times after this post. 1st time the problem was very minimal. It took a long time to start to heat up at idle and any forward throttle at all and no problems. 2nd time old symptoms came back. It was odd that there was a change in the symptoms.

That's one way to fix it!

[surferbobo]

I am having the same problem with my 08 VLX. It only started after we started it up after the winter. Had it winterized by the dealer and had it outside all winter. The dealer summerized it and then the first time in the water we were idling around and the high temp alarm went on. I speed up the boat and the temp went from 200 to 140 in 5 seconds.

I took it back to the dealer and they looked at the impeller and said everything was good. I took it out again and it the temp guage was all over the place. Took it back to the dealer again. This time the Malibu factory guys were there doing the make it right services. They hooked the water up to it and ran it - the temp was all over the place. They could not figure it out. They took the thermostat out and replaced it with a new one. Also replaced the sending unit.

Today I took the boat out again. The temp went to 160 and stayed there for 1 1/2 hours. Thought everything was fixed. Then we went surfing and we were idling changing riders the high temp alarm goes off again. Temp was 200 so I put in it in gear and speed up to 10 mph and the temperature dropped to 140 in 5 seconds.

Another thing we noticed was that when surfing we had alot of steam (exhaust) coming from the back of the boat. Dealer said this normal when the lake is cold (44 degrees).

Going back to the dealer on Monday.

[FFCole411]

I am taking my to a mechanic on the 28th, will keep you updated on the problem. I put in a new temp. gauge. This one actually gives me the readings of the temp. After doing some tests the other day, figured out it was dropping from 200+ degrees to 155-160 degrees at WOT. At idle is when temp. is going up. I told the mechanic what was going on over the phone. He said it sounded like some sort of blockage that at idle wasn't allowing water to get through the system and at WOT it was making it through. I also noticed the other day when I put it in neutral and rev the engine up the temp is coming down. As mentioned above, taking it in on the 28th and hopefully get the problem solved.

Cole

[JUST-IN-TIME]

i would inspect the impeller and housing first and back flush

[Sunsetter95]

I have heard of a few other things but they may not app;y to your case. I have seen the inside wall of a hose be partially collapsed which caused a restriction. I have also heard of the heat riser gaskets blocking the water holes. But like I said I don't think that applies to yours. Do you have a seacock on yours? If so, is it opening all the way despite where the handle is positioned. Was the pump housing installed in the correct position. Mine could go in two positions. One for the right side of the engine, and one for the left. Belt tight enough? That is about all I can think of besides what you have done all ready.

Edited April 19, 2009 by Sunsetter95

[the_dude]

May have found the culprit. As I mentioned above i planned to change out the motor anyways due to an over rev accident that occurred a while back. While swapping the motor over the weekend i discovered that low and behold the tranny cooler had quite a bit of foliage in it. I picked up quite a bit of reed looking material. There were even a few random bits of impeller from long ago.

The last time I had taken the boat out I couldn't do the inspection for fear of damaging the house that connects to the trans cooler. It was not in the greatest shape and I felt that I would destroy the hose getting it off. I replaced the hose when swapping the motor so I was free to destroy it getting it apart

Haven't fired the new motor yet but I'll update you guys if it didn't fix the problem.

[JUST-IN-TIME]

yea i think you found it

most shops do not flush, even if the impeller comes out all in 1 piece

I always back flush no matter what

I have seen pieces fo into the v-drive also on some boats

[Serg22]

Hello I’m having the same issue with my Searay. Can someone give me detailed instructions on how to perform a back flush? Thank you