The Boating Forum - High Idle Overheating...

I have a 1995 Nitro Bass Boat with a 1995 150HP xri EFI outboard motor. The boat developed overheating problems last year...when you idle or go fast..no problem, but if you cruise from 1300-2000, then it goes up past 180 degrees (I don't know how much farther, I stop and let it cool down!!)..if I let it idle again or go full throttle, the temp gauge immediately drops. The garage that worked on it found a leaking right bank head gasket, and a hole burned in the Intake/exhaust divider plate. That fixed the problem. Now. almost six months later, it's doing it again. I decided to do this job, to save money, (I used to be a mechanic). I just removed the divider plate, and it looks fine. There is a scant amount of water stain down below one bank, but it's not impressive. I don't think that it's a leaking head gasket though. The garage told me that maybe the transducers that are mounted in the back of the transom may be interfering with water intake, or that the hull may have a "hook", what's your take, and should I go ahead and pull off the caps and replace the head gaskets, as well as getting the heads milled? Thanks, Blaine-Merced, CA

Unusual. Is there a water PSI gauge on the dash?

sorry..yes there is...it reads 15 PSI at that range and 10-12 PSI at idle. It goes up to 20+PSI when I have it open throttle...

sorry..yes there is...it reads 15 PSI at that range and 10-12 PSI at idle. It goes up to 20+PSI when I have it open throttle...

sorry..yes there is...it reads 15 PSI at that range and 10-12 PSI at idle. It goes up to 20+PSI when I have it open throttle...

That engine have the poppit valves?....because that is the rpm range where it will definently affect it if it does...., Evinrude had a defective batch on some etecs....we had one....it didn't overheat but one cylinder bank on the starboard engine would repeatedly climb into that nervous zone...., water was leaking past the poppit valve seal...., they replaced it and no problem....but that is the identical rpm range....same thing....slow down,...cooled right off, sped up...cooled off....but it did not like the 1100-1600 range at all....I know Yamm's have had some issues with a few of there's as well.

RButterworth
30 Grady Marlin
250 ETECS

Mine turned out to be a stuck poppet valve. It un-stuck when I took the valve apart and put it back together - never gave me any more trouble after that.

Causes of this problem are probably various and many, but I had a 135 v6 Merc that did the same thing. Ran cool up to about a fast troll and on plane, but in between trolling and planing speeds the temp would rise. Fortunately, my tolerance was lower than it's . . .

Than the poppit valve it stuck! :o
3-7 PSI at idle and 12-15 any other time.

are those hard to replace...I believe that it's on the passenger side of the motor...I just bought a REAL manual, so I am sure I kind find it....what you say sure makes sense....

I just tore apart the lRight end cap (cylinder head), it's definitely leaking on the bottome side?....my quandry, should I get the heads milled?

OK..it's been awhile.I replaced the gasket, diaphragm, and spring on the poppet valve, I replaced the leaking head gasket and divider....still overheating from 1200-2000..also if I leave the boat in neutral from 1200-2000, then there is no overheating...I need help!!!!

Also..just for reference..what would happen if I removed the poppet valve completely?

If you leave the boat in neutral and it doesn't overheat...that would lead me to water turbulence around the intakes....that's a pretty large rpm spread though..., timebandit may have an answer for you....it's got to be frustrating at this point.

Just for testing, you could try droping the engine down one hole.

If you decide to change the water pump install the impeller with the brass hub.

Same part number as the old one but the last two numbers/letters are T4.

I have resolved allot of mid range overheat issue wit this impeller. The T4 is used on Merc race engines and the merc production engines use the impeller that have a nylon hub.


89984T3 nylon hub

89984T4 brass hub.

bshultzrn - 9/9/2007 2:23 AM

Also..just for reference..what would happen if I removed the poppet valve completely?

If it is removed the block won't fill up with water. :nono:
These are touchy. Get new thermostats if you have not already. Don't over tighten the poppit bolts. The gasket is cork and will squish. The diaphram needs to be sealed. Put perfect seal around the rim of it and the gaskets. Just snug it up.

Now that you guys mentioned it..it looks like the engine had been moved up a notchon the bracket...if it's too far up..that could lead to too much turbulence....I out the poppet valve diaphragm in without sealant..so maybe I'l do that as well...any other advice?..thanks for your help...

I have a 95 XRi 150HP that does the same thing, I guess it isn't just mine. Mine climbs up to around 170 when I run it around 1000-1400(slow speed no wake zones). Drop it to idle and the temps will level off around 150, hit the throttle and it immediatly drop to 140. I know my engine is mounted high on mine, but with the low water pick-up I have this shouldn't be a concern. When running at this speed water pressure is good(6-10 pounds), but I don't see much from the pee stream. Compression on mine is 128 all 6 holes, and it was a freshwater motor until 3 months ago. I replaced both T-stats and a complete water pump kit with factory parts, no change. I'm going to replace the poppit valve soon, but my water PSI seems fine. I get 6-7 at idle with t-stats closed, drops down to about 4-5 when stats go full open. PSI stays pretty close to 8-13 until I hit 4500, at which point pressure will climb up to almost 25 at WOT. I've never had an alarm go off, but would like the temps on it to stay down like my old 150 did(81 2.0L).