Honda 150s overheating

[kevin ware]

Has anyone had this problem with their Honda engines on a Tom Cat powering down due to an overheat warning?

When running the Honda 150s at about 3000 RPM with the engines at +1 tilt (lower unit closer to the transom), at random intervals the engine overheat alarm sounds and the engine automatically reduces power to idle. Both engines have done this, but not at the same time. It has never happened (at least yet), with engines at +3 tilt or greater.

I suspect the problem is related to related to inadequate cooling water intake, perhaps due to cavitation near the intake with the boat on a plane, and the engine tilted close to the transom. Mechanic has found nothing wrong with the engines, intake or pumps.

Ideas?

Kevin Ware
Tom Cat 25.5

[thataway]

I would look at where the cavitation (anti ventilation plates) are when on a plane. They should be running right at the surface. If the engine were up too high or too low, there could be increased cavitation or water starvation...We never had that on the Suzuki's even with radical down trim and the Permatrims, trying to get planing speeds down at 9 to 10 knots.

With a 2007 boat you should have the 24" bracket (only a few of the early boats had the 36" bracket--which should require the outboards to be mounted higher.

[Dreamer]

Been there! There are three temp senders on each engine. In the Honda manual, there are ohm. values for them, hot and cold. I tested them cold and then in hot water and found one out of range. Once it was replaced, no more overheat light. I no longer have the boat and manual or I'd give you the numbers.

[kevin ware]

Have not had a chance to check the temp senders, but will do so.

However, Honda dealer mechanic today says he doubts a sender issue, because it has happened on both engines, and it is unlikely there would be that problem occuring at the same time on different engines.

His thought was that the Honda engines mounted on the 2007 Tom Cat are too far out of the water. He says with a 24 inch outbound mounting platform on the stern, the cavitation plate should be no more that 2 1/2 inches above a line carried back from the transome and following the lowest point on hull. We did that measurement with a straight edge and found the Honda's at 5 1/2 inches...that is a good 3 inches too far out of the water.

Unfortunately, with the engine mount installed by the manufacturer, it is not possible to lower these normal shaft length engines any more than an inch further (which he is doing) without altering the aluminum extension itself. (Of course, if the engines were long shaft models, this would not be a problem).

Interestingly, a friend involved in the boat design and building business pointed out this very thing to me some time ago when seeing the Tom Cat out of the water, and then mentioned it in passing to an acquaintance who worked for Sea Dory in the mid-2000s. This fellow told him yes, those Honda normal length engine shafts were too short for the installation, and a long shaft would have been better, but at that time the company had much greater concerns than finessing engine installations.

I do not know enough about this to draw any definite conclusions, and am a bit puzzled that if all the above is true, why other owners have not been noting the problem.

In the meantime, will lower the engines down about an inch, and avoid tilting them parallel to the transom (which drives the bow down, and the stern up, further raising the water intake).

Was also considering moving the house batteries from the stern, to the port side, mid-cabin, but am now having second thoughts about doing that, because it would further raise the engines relative to the water line.

Comments?

Kevin Ware
Tom Cat 25.5

[letitride]

My 2008 honda 150 was overheating at >3k rpm there are 2 thermostats on top of the motor opened it up and found them both almost completely crusted with salt cleaned them up and all fixed took 5mins to pull them and 1 hr to clean them. Previous owner must not have washed the motor out after with fresh water.
I would check both thermostats and proceed debugging really easy.
Hope you find the problem.

[Wefings]

If this just started happening , its probably not engine height. The engines should be XLs meaning 25" . We have never had the problem on a Tomcat . Cats are different than monohulls and most folks "go for what they know" which is monohulls . I would look at those sensors, water pumps , cooling passages, T Stats , etc, before moving motors if this is a new problem .Honda sensor failure is not that uncommon.
Marc

[Dreamer]

I agree with letitride on the thermostats. However, flushing with fresh cold water doesn't help much in that area. As soon as the cold water hits, the t-stats close!.I removed all 4 once or twice a year and soaked them in Salt-A-Way. If you have water pressure gauges, the ports for them on the thermostat housing will plug up with salt also and have to be drilled out.