1990 ProV 150 Overheating

[MNY4m4h4]

I have a 1990 ProV 150LD that has me at my wits end. The motor runs great but overheats at idle.

I bought this used and when I first replaced the impeller I saw signs of overheating. The plastic around the cup was a bit melted. It seems reasonable to assume the old impeller burned up for some unknown reason and the seller simply replaced it and dumped his problems off on me.

I have performed the following in order as listed and I still get a weak tell tale stream, 0 pressure on the gauge (gauge could be broken), and goes into alarm in about 5 minutes.

Replaced water pump, impeller and housing
Cleaned out tell tale hose and nipple
Replaced Popit, rubber grommit, and gasket.
Replaced both thermostats and gaskets
Replaced temp sensors
Pulled water jackets on heads, cleaned and replaced gaskets
Pulled Heads and cleaned water jackets and replaced head gaskets
Pulled exhaust manifold (one that houses popit) cleaned water jackets and replaced both gaskets.
Ran a camera up the tube from water pump to bottom of powerhead and didn't find any blockages.

I was convinced I had a blockage in my cooling system but found nothing when I pulled it apart and cleaned it. I just put heads and and exhaust manifold back on and ran to launch to test and she still had the weak stream and alarm came on in first five minutes.

Heads, jugs and cylinders all look great and like I said the motor purrs but gets hot at idle. If I take it up to 1500 rpm or more then I have no issues, she only overheats at low rpm.

I really hope there is a Jedi Master Yamaha Mechanic that reads this and has seen this before!

Defeated in MN

[99yam40]

Replaced water pump, impeller and housing


Did you use the kit with cup and wear plate?

[MNY4m4h4]

Replaced water pump, impeller and housing


Did you use the kit with cup and wear plate?

Yes, replaced with factory Yamaha kit, all the way to the keyway

[99yam40]

How did the passages look when you pulled it all apart?

[MNY4m4h4]

How did the passages look when you pulled it all apart?

They looked really good, in fact the motor is in awesome condition for 25 years old.

I was hoping to find a clear blockage but found nothing. The only issue I saw was on both head gaskets there was a small tear on one end where the gasket is solid and covers a pocket. The gasket looked like it had sucked into that pocket and had a small tear in it like someone poked it with their finger.

That pocket in the head doesn't have a port or go anywhere, but I was hoping it was somehow causing the issue because I saw nothing in any of the water jacket passages to show any type of blockage.

I expected to find something and when I didn't I was hoping that a full cleaning of the water jackets and new gaskets fixed the issue....sadly it didn't.

[99yam40]

Maybe there is some disturbance causing air to be sucked into the water pump, but I would expect that to be at higher speeds.
Maybe exhaust getting into water flow

I would think about dropping lower unit and hooking up a water hose to the tube leaving water pump. turn on water and crank up motor to see if that would let motor run without overheating.
At least that would say if problem was in power head or maybe lower unit

[MNY4m4h4]

Maybe there is some disturbance causing air to be sucked into the water pump, but I would expect that to be at higher speeds.
Maybe exhaust getting into water flow

I would think about dropping lower unit and hooking up a water hose to the tube leaving water pump. turn on water and crank up motor to see if that would let motor run without overheating.
At least that would say if problem was in power head or maybe lower unit

Makes sense in that it would either identify or eliminate the water pump from being the possible problem. That said, it seems kind of wild westish ...... not gonna F up my motor doing this am I?

[erniefish]

No, you will be fine,the water hose on the pick up tube will answer your question, also a great way to flush a motor if used in salt water . Let us know what you find

[MNY4m4h4]

I'll give this a go and post the results

[zenoahphobic]

Prima faces sounds like water pump - they are fickle
You said burning on previous pump housing; this raises the possibility that a previous impeller may have also broke leaving a small piece stuck in a passage somewhere. I hope not because if the case you may again have to pull it apart.

[zenoahphobic]

Reverse flushing into thermostats housing with thermostats removed. But don't spray water everywhere.

[MNY4m4h4]

Prima faces sounds like water pump - they are fickle
You said burning on previous pump housing; this raises the possibility that a previous impeller may have also broke leaving a small piece stuck in a passage somewhere. I hope not because if the case you may again have to pull it apart.

Thought the same initially as it made sense, which is why I pulled it all apart specifically looking for a chunk of an old impeller lodged someplace in the system but found nothing. All I found was clean water jackets, not that that is a bad thing but was hoping to find an obvious blockage.

[MNY4m4h4]

Update:

I dropped the lower unit and hooked up the hose to the water tube and before I even started the motor it was pissing way more than it was at the launch.

I started it up and let it run for 10-15 minutes and got no alarm. The water pressure gauge does work and was reading 18-20 PSI.

I did make a video but I don't know how to upload it. I can pull the heads and extract 8 snapped off bolts in the block (not head bolts) but I can't post a video...lol

So it's probably the water pump....what could I have done wrong when I replaced it?

[99yam40]

Using wrong parts are the only thing I can think of at this point

I dropped the lower unit and hooked up the hose to the water tube and before I even started the motor it was pissing way more than it was at the launch.

With water pump( lower unit) removed starting the motor will not increase water flow

[MNY4m4h4]

If the popit valve is somehow stuck open would I read zero pressure at idle or is this most likely the water pump?

Obviously the hose had enough pressure on it to put out a lazer beam stream from the tell tell, but I wonder if it was so much pressure from the hose that it was masking the issue at low RPM, as like you stated without the lower unit attached there is no water flow function being performed by the power head.

I have always had good cooling at speed in the water, which would naturally increase the pressure on its own.

What kind of pressure will a properly working water pump put out at idle?

In theory I could hook the hose back up and back off the spigot on the hose to a water pressure that would simulate a working water pump at idle and see if it goes into alarm

I'd like to narrow this down and see if I should be buying a new pop it spring (I just replaced the grommet) or if I should just buy a whole new water pump assembly and try that one more time.

So far you guys have been a great help…..I felt great to see that good stream last night.

Thanks in advance.