[milo98]

I have a 1998 Mercury Optimax 135 that I recently purchased used. The engine temperature sensor comes on between 2,000 and 3,000 rpm, but if I accellerate to 4,000 rpm, the alarm goes off. I was reading the article about the tropical poppet valve on Kencan's motor; do you think this is a similar problem? the dealership claims that they have had a mercury rep in to look at it and that he has given it a clean bill of health. Every time they have operated the boat, they couldnt get the alarm to come on for them. I can get it to come on at will. Any info would be greatly appreciated.

[vinney]

There are two different tempure sensors. One is on the air compressor. The other is on the cylinder head. The tempure light comes on at 173 degrees. If its intermitting you will only find it with a scan tool. Mercs scan tool is a DDT. It has an light on the top that will come on when the engine light is turned on. I have had the customer run there boat with the ddt hook up so I could look over the stored data. It will store past and present data. The other way to find out what is going on is to use a heat gun. Run the engine and watch the cylinder head tempure. It shouldn't run above 150 degrees. If the bypass valve is leaking it will effect the water pressure at idle. I think you probably have a spun hub on you water pump impeller. I would replace the impeller with a factory impeller and factory thermostats. You are loosing pump volume.(spun hub impeller). Vinney

[milo98]

I appreciate it... but I am a little confused as to how the impeller could turn in the housing once the hub has spun. I am assuming you mean that the rubber portion of the impeller is no longer attached to the metal portion with the keyway.Impellers are a rather tight fit, so I dont see how the inertia of the shaft could make the impeller spin unless the fins of the impeller were wore out.The dealer claims that by examining the past data of the ddt that the engine has never been hot.Its particularly annoying, because 2,000-3,000 RPM is where my boat cruises good.

[vinney]

We define a spun hub. (impeller) The impeller has two parts the incert and the impeller. The incert can be made of brass,alu.and plastic. The rubber is the other portion of the impeller. The incert and rubber are bonded together. They can turn inside each other.(spun hub). The drive shaft drives the impeller when you have a spun hub the incert is spinning at a different rate than the rubber. That is when you get low pump pressure and volume problems. The impeller itself can be worn on the outside of the rubber blades and cause low volume problems. If the engines been dry fired you can hert the impeller. I would still go after the pump if the engines running hotter than it should at 2000 to 3000 rpms. There is a problem with some of the water tubes that run from the pump to the power head. rotting out. This causes poor pump volume. Vinney

[milo98]

I havent had a chance to look at my motor since your last post, Vinny, but I was wondering if there was a way to check the pump volume without tearing the engine apart? Also, the dealer INSISTS that he has had the engine on a dtt scanner and that it never got hot.Sounds like I either have to do this myself or get another mech. what do you think?

[EVMIII]

Did the dealer actually put the boat in the water and operate it to test or did it perform tests in the shop? I had a heat alarm sensor problem (short in sensor)that caused the alarm to sound based on the wire moving in the housing. Happened everytime with the movement/bouncing of the boat, but would never happen in the shop. Just a thought. Good luck.

[vinney]

You can put a water pressure guage on the engine most of my fish guys have them. If the engine sensor is thinking the engine is hot it will go into rpm reduction. The only way you are going to find out whats going on is to prove or disprove whats going on. You either need the ddt scan tool or get a heat gun for 100 bucks and run the engine with the cover off and shoot the thermostate housing. It should run no more that 150 degrees. You need to prove to the tech its overheating. I will let my customer run his boat with one of our ddt hook up and when he returns we will look over the data. The ddt stores active and history.If it hicup it will store it. If the sensor trips rpm reduction you will know it. The engine light comes on and the engine goes into reduction. You need to do some work for your tech. I not saying that you should have but sometimes you have to take matters into your own hands. If you find the problem i bet 100 buck he will be up for listing next time. I never tell a customer no problem found I think its an insult if someone has a problem or complaint you need to follow it up. Prove or disprove. If you use tools instead of guessing you can go wrong. Vinney

[vinney]

You can put a water pressure guage on the engine most of my fish guys have them. If the engine sensor is thinking the engine is hot it will go into rpm reduction. The only way you are going to find out whats going on is to prove or disprove whats going on. You either need the ddt scan tool or get a heat gun for 100 bucks and run the engine with the cover off and shoot the thermostate housing. It should run no more that 150 degrees. You need to prove to the tech its overheating. I will let my customer run his boat with one of our ddt hook up and when he returns we will look over the data. The ddt stores active and history.If it hicup it will store it. If the sensor trips rpm reduction you will know it. The engine light comes on and the engine goes into reduction. You need to do some work for your tech. I not saying that you should have but sometimes you have to take matters into your own hands. If you find the problem i bet 100 buck he will be up for listing next time. I never tell a customer no problem found I think its an insult if someone has a problem or complaint you need to follow it up. Prove or disprove. If you use tools instead of guessing you can go wrong. Vinney

[vinney]

JB I dont know how it doubled up the reply. Thanks