Nissan 35 fourstroke hot idle problems

"I have a two year old Nissan

"I have a two year old Nissan 3.5 long shaft 4 stroke that I use as an auxiliary on a 19 ft sailboat. Most of the time this motor runs flawlessly, starting on the first or second pull and has a steady idle. However, when run for longer periods of time, like an hour or more at half-throttle, the motor will not idle when hot. It runs perfect as soon as the throttle is opened again but the idle circuit becomes inoperative. After the motor has cooled all returns to normal. Does anyone else have this problem? Is there a fix?"

"Your first step is to take it

"Your first step is to take it into a dealer to find out why the engine is getting hot. That can be anything from a water pump problem, thermostat problem, oil problem to an operator problem. There isn't anything inherently wrong with the design so there can't be a "fix" as such. Usually the problem with an overheat is that the water pump pick up point is obscured or was blocked at some point causing the impeller to become prematurely worn. Frequently plastic bags will get sucked to the pick up causing the impeller to run hot...When you stop the engine the bag floats away and you have no way of knowing what caused it to begin with. Even running the engine in sand or grass can wear out the impeller so that it becomes to degraded to cool the engine at high RPMs. On the other hand, its always possible that your engine could have a part failure. But you have to get it into a dealer as your first step."

Dave I also have one of these

Dave I also have one of these and the 3.5 has a very poor water pump. As the pump wears it will not pump water past the thermostat. The weep hole will show water discharge but it has not cooled the engine. I suggest that you totally remove the thermostat or at least put one with a lower opening point.

"This motor has maybe 50 hours

"This motor has maybe 50 hours of use since new. Discharge from the weep tube is plentiful, and at quite a good pressure, so I am not too concerned about a pump problem yet. Checking the thermostat sounds like a good first step. Does anyone know where it is located on this engine and what the opening temperature should be?"

"You need to take it into a de

"You need to take it into a dealer as the engine is under warranty. However, the thermostat is located on the port side of the engine block and begins to open at 125 degrees. It should be fully open at 140. The likelhood of you having a thermostat problem is less than one in a 1900 based on warranty claims since that model has come out."

"I bought the motor online fro

"I bought the motor online from Cabela's and, consequently the local Nissan dealer (who is a couple french fries short of a happy meal anyway in my opinion) doesn't want much to do with it other than selling me parts.

However, I have quite a bit of experience as a mechanic and am comfortable working on it myself. Tohatsu Guru, do you have a suggestion as to something to check before looking at the thermostat. As I mentioned before, other than the hot idle issue, the motor runs flawlessly and, even hot, only the idle circuit is affected. I'm concerned that I may have a really elusive problem like a crack in the carburetor die-casting that only opens up when the carb is physically warm, as it would be after running for a half-hour or more."

"Think in terms of KISS. While

"Think in terms of KISS. While you could always have some sort of rare mechanical defect, its just that....Rare. Eliminate the the most common possible reasons first. Worn water pump parts, application error(heavy sea causing the engine to come up to high), blown head gasket, etc. In my 46 years of working on outboards I have never seen a cracked carb that opened up when hot. But, I have seen tens of thousands of worn water pumps.

Also, I would let the dealer have at it anyway. In the end he gets paid a crap load of money to work on your engine under warranty(if it is a warranty problem). Most dealers are desperate to keep their doors open and aren't stupid enough to turn away service work in this economy. If your local dealer is an idiot I would suggest calling Tohatsu/Nissan at 972-323-6003 and asking them to intervene. They can light a fire under all but the densest of lead bottoms "

"Thanks Tohatsu Guru, your log

"Thanks Tohatsu Guru, your logic rings true. I'll check the most probable things first and think about giving the dealer another chance. It never hurts to put in a fresh impeller......."

"Look at the wear plate and th

"Look at the wear plate and the liner really closely. We always replace with a kit as any wear on those two items will cause premature wear on a new impeller. No lines or grooves allowed. You would be surprised how many people think wear marks on them are actually machined"

"Follow up:

I pulled the th

"Follow up:

I pulled the thermostat cover off only to find the thermostat and it's cavity full of salt. The downstream side was clean. Once the deposits were removed the thermstat functioned correctly heated in a pot of water on the stove.

I think it is clear that the way I use the motor and, more importantly, the way I flush it does not allow the engine to run long enough to fully warm and open the thermostat. As a sailboat auxiliary, 90% of the time the motor is only run for a few minutes to pull away from the dock to an area large enough to raise sails. When becalmed, the engine will be run for a longer period, but that is rare here on San Francisco Bay."

I'm actually surprised tha

I'm actually surprised that salt was the cause. Try switching over to a 10w-30 oil and only fill the engine up to the lower mark on the cap/stick. Anything you can do to raise the operating temp would help. Avoid synthetic oil as well.