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Overheat Problem - Yamaha VMAX 150

R

robrich

New member
I am having a devil of a time diagnosing an overheat on my 2004 Yamaha VMAX 150 (model number V150TLRC ). Initially, I had two problems – poor carb adjustment and an engine alarm (either overheat or oil alarm).

During my troubleshooting, I cleaned and adjusted the three carbs. That problem is solved. And engine runs a lot better now!

Still have the engine alarm to deal with. My gauges don’t tell me if it’s oil or heat causing the alarm, so I replaced the oil pump as it was old. Problem was still there. I used an IR heat gun on the heads during the next alarm, and the temp was in the high 160 range if I recall correctly. So – overheat. This is a 2004 and I run her in salt water on the Texas Gulf Coast, so I decided to replace a lot of the parts as they are over 10 years old.

  • Replaced Water Separating Fuel Filter
  • Checked Fuel Ball – all okay
  • Checked fuel flow to carbs (using Fuel Ball) – all good
  • Replaced Oil Pump (remote tank)
  • Replaced Spark Plugs
  • Replaced fuel pumps
  • Replaced Thermostats
  • Cleaned Poppet valve

I thought I might have a lean mixture problem, so I ran the boat this weekend and adjusted the fuel screws to a very rich mixture (4 turns out from closed). Still had an overheat.

Last night I removed the head covers and heads and inspected cooling passages. Everything looked pretty good for a 14 year old motor. No significant blockages.
The impeller has less than 8 hours on it, and the tell-tale is streaming water at full strength. Everything seems to be just as it should be, but I am consistently getting the overheat and limp mode after 5 minutes of operation at 4000 rpm. Allowing the engine to idle for 10 to 20 seconds will cool the engine enough for the alarm to turn off.

Anyone have any ideas of what the problem might be? I am totally stumped.
Rob
 
Last edited:
You haven't mentioned thermostats and have you checked the poppet valve which should allow extra cooling water through at higher rpm?
 
Sorry, disregard that, just re read your post. Try disconnecting the temp sensors and run it hard for a short while to see if it is actually getting hot, it could be a faulty sensor.
 
Thanks iang6766 - I have checked the temp on the heads with an thermal infra red gun and they do get hot enough to sound an alarm, so the sensor seem to be acting correctly.

I bought access to the Yamaha manual through this website and I am following the troubleshooting steps. I just cleared out all the cooling passages and ensured water was flowing to each cylinder bank. The water seems to flow a little better on the Left bank, and the Right bank seems to get about 80% of the flow that the Left gets. I don't think that's enough to cause an overheat, but it's worth noting. I also don't know if that's just normal for this engine, or if there may some restriction deeper in the motor.

My next step, now that I have cleaned the water passages in the head and around the cylinders, is to install the new head gaskets and see if the problem is still present. Should be pretty easy to tell after a little testing.

Any other suggestions anyone?

Rob
 
Soooooo- new headgaskets and head cover gaskets. All the water passages are clean, waterflow is good, and new thermostats are functioning. My IR heat gun shows the head covers at 128 degrees at idle. Both sides show this now, which is good.

I ran her at about 3000 rpm on the trailer at the ramp last night for 10 minutes - no overheat problem. I think launched her and did a few laps in the area close to the launch. in less than 5 minutes, the overheat alarm came on and the boat went into limp mode. It recovered within 20 seconds when I put her to idle. I couldn't even get the cover off to take a heat reading on the heads before the alarm silenced itself.

I am beginning to think it is either a bad temp sensor, or a bad poppet valve. I plan to test the heat sensors today. I have a poppet valve on order. I also plan to change out the 4 month old impeller, just in case.

Any other possible ideas guys? This is getting to be an epic freakin' troubleshoot.

Rob
 
Your last resort will be to remove the exhaust plate and and inspect the little cooling water slots in there and failing that you will have to remove the powerhead and checjk where water passes through the sandwich plate.
 
iang6766 said:
Your last resort will be to remove the exhaust plate and and inspect the little cooling water slots in there and failing that you will have to remove the powerhead and checjk where water passes through the sandwich plate.
Click to expand...


Thank you IanG - I will put that on the list.

This weekend I tested both thermoswitches extensively - they both operate within spec, so they appear to be reporting the overheat correctly.

I had a spare impeller, so I changed it out. The water flow out the tell tale was much stronger than it was previously, so I am beginning to suspect a worn impleller that was not getting enough flow through the powerhead at higher RPMs.

I will keep this thread updated in case other VMAX 150 owners in the future run into this problem.

Thanks all for the advice!

Rob
 
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