Engine help 2000 Scorpion - Mercruiser

[Wish]

Buddy's boat- 2000 Gekko

 

Replaced: tstat, manifolds, risers. Rebuilt raw water pump, new impeller. Checked/cleaned heat exchanger, transmission cooler. Checked water pick-up. Checked hoses from tstat housing to manifolds. Inspected tstat housing. No issues or clogs or narrowing.

 

Problem is temps still in 180-190 range and one manifold is warmer then the others.

 

Thoughts?

[Gloersen]

laser temp gun read each cylinder above/near the plug. may be clogged cooling passages/head (corrosion/gunk/fragmented impeller blade, etc.) Check them all with engine fully warm at idle.You'll get an idea pretty quick if any cylinder or more is way out of CHT range.

[Orlando76]

All inboard engines have 1 manifold that's hotter than the other. Look at the the tstat housing, it's always closer to one manifold, PCM it's the starboard side, water flows path of least resistant..... On my 75 & 76 Ski Nautiques with dual exhaust, when cranked in the driveway, starboard side shoots water 6 feet farther than the other. Maybe I missed it but did the hoses get changed? I suspect it's sucking air, usually at the tips of the hoses, usually not noticeable. 180 isn't bad, actually ideal but gives lesser room for error.

 

[Orlando76]

To help pin point and for giggles, bypass the PITA water strainer if equipped and replace hoses from pickup to cooler then cooler to RWP and see what happens.

[gregy]

What temp T-stat did he put in? Seems a little odd that its staying at 190ish. Might even be guage, wiring, or sensor? You could stick a non-electric gauge in to verify temp.

[DW]

@Wish: did you check the inside of the raw water pump to ensure no scores or gouges in the housing? Sometimes I get impellers that must be "softer" than ideal and temp runs a bit higher than expected.

[Wish]

@DW he did say he rebuilt raw water pump and he's a gear head so guessing yes but I will ask. He also has the link to this thread and is checking it periodically.

 

He wanted me to add that the gauge swings from 170-195 and then back down again in about a minute and a half for the cycle both ways. A pulse reading in other words..up then back down..then back up and so on. This occurs at any RPM motor fully warmed up.

[oldjeep]

Sounds like a bad/wrong thermostat to me

[DW]

@Wish: is the swing random or in synch with either loading the engine or does it tend to spike when the engine returns to idle after pulling a skier or running under load? If totally random, I would check the gauge ground or connection & hose clamps for tightness particularly on the pump inlet side.

[Wish]

much as described. So he set the RMPs at 2500 and watched it cycle up and down and back up in that minute and a half time frame. Same occurs at 3000 and 4000 as random checks. So basically all RMP sets it repeats that up and down cycle of readings.

[oldjeep]

Sounds like it has a 190/195 degree thermostat in it. Stat stays shut until 190/195, opens dumping ice cold lake water in that quickly drops it to 170 - cycle repeats as long as the engine is generating enough heat to get to 195. Typical Marine 350 has a 160 degree stat in it.

[pkreusch]

Okay, I'd like to introduce myself. I'm the silly bugger that owns the 2000 model Gekko GTR22 with the one-off Black Scorpion Mercruiser engine. Thought I'd go ahead and get in the conversation since doing this through a third party (my good buddy "Wish") is getting a little cumbersome. Thanks Wish for posting and a big THANK YOU to all who helped so far.

 

Here is what I know:

The 2000 model year Black Scorpion is a quirky motor that has a "cool fuel" cell, and no strainer (other than the small holes in the heat exchanger :) ). I replaced the tstat last year, checked it in hot water on the stove (2 times, once last year and once last week) and it opens fully at 160. It is stamped 160. I feel like Arnold Swarzeneger.... (in my best Austrian accent) "It's nott ahh tuumorr". :D It's really not the tstat... Although I will probably remove it to completely rule it out.

 

Last season it slowly (over 5-6 months) started showing signs of higher operating temps While skiing. We attributed it to the age of the manifolds and this year purchased and installed new ones. The problem is still persisting. I took it to the local river here where I could get a good long test drive. I started out at 2500 RPM fully warm and started to drive. The temp slooooowly rose to 190-195 over a 45 second time frame. Without reducing RPM's the temp slooooowly fell back to 160-165 over the next 45 second time frame. This "rise and fall" of the temperature continued for a 15 minute ride at 2500 RPM. I checked again at 3000 RPM and 4000 RPM with the same results using the same testing method and testing times.

 

Checked these items so far:

Water pickup

Hose from pickup to RWP

RWP/impeller

Hose from RWP to trans cooler (heat exchanger)

trans cooler

Hose from trans cooler to cool fuel cell

Cool fuel cell

Hose from fuel cell to tstat housing

Tstat housing

Thermostat

hoses from tstat housing to brand new manifolds

No blockage, no bad hoses.

 

Next on my list:

Engine circulation pump

Mufflers

Blocked water passages in the heads

Head gasket(s)

 

Any help?

Thanks

P...........

[pkreusch]

@Gloersen - Bought a laser temp gun and got inconclusive results. Temps varied when read above and below each plug but overall seemed to be consistent across all measurements. nothing really measured above the operating temperature.

[pkreusch]

@Orlando76 - The hot engine water exits through the tstat housing where it is equally distributed to 2 exit passages. Neither path is resistively further than the other. I did find a small water leak on the pressure side of the hose connector that is located in the middle of the trans cooler to fuel cooler hose but this would not suck air. This is where the hot water shower is tapped into to get it's cold water for tempering. The last few times I had it out I had more than usual bilge action and I suspect this is where the excess water was coming in. I'll check again for small air leaks. Thanks for the suggestion. I will probably switch out the tstat-to-manifold hoses for clear tubing so as to see if any air bubbles are being generated from the engine.

[pkreusch]

@gregy - I'm ruling out bad gauge/wiring/temp sender from the way it cycles to warm and back to cold. the gauge appears to be working correctly and is consistent with the measured cylinder head temps.

[pkreusch]

@DW - Rebuilt RWP last year. Ruled out. No scoring.

[DW]

On the Mercs there usually is a water relief device to ensure the manifolds always have water flowing though them. The device has 2 white balls attached to a bar with springs that force them in the closed position until water pressure opens them when the thermostat is closed to allow water to flow to the exhaust manifolds. Check the springs to make sure they are working, having one manifold warmer might be an indication of a broken spring.

 

Could there be a recirculation issue with the way the hot water shower is configured?

[thager]

I have had a similar experience with a 73 Hydrodyne. Had to be real careful with first lake runs of the year. Manifold would develop an air pocket and that manifold would be hot to touch and other manifold cold. Cure was to bleed hoses until good water flow from the hose then tighten up.

[pkreusch]

@DW No balls, no springs in the tstat housing. Where would said balls be located? The housing directly short circuits the raw water to the manifold path AND to the engine circulation pump path. The engine circulation pump provides positive pressure to the engine for cooling. This arrangement will mix hot water from the engine with all the raw water pump can give to cool the manifolds at all times. I'll try to post the water flow diagram shortly.

[DW]

@pkreusch: the ball/spring/rod device is located in the thermostat housing. In ones with the setup, there are 4 ports that feed the exhaust manifolds, so if you only have 2, as you commented, probably don't have that system. The system basically serves as a water bypass for when the tstat is closed to ensure water always flows through the exhaust manifolds.

[pkreusch]

Light bulb just went on.... I'll bet the small engine bypass hole that allows small water to bypass the thermostat is blocked. I'll check tonight when I get home. Now I just have to find it....

[Jordan]

^^^ That would explain the swinging temps

[pkreusch]

@thager Thanks, but it doesn't seem likely with the riser setup that I have. By design, the air pocket would be forced out the top.

[Waternut]

Thermostat installed backwards? If the bypass hole starts allowing really hot water through, it would still open the thermostat but only for a short time. Have you tried running without the thermostat yet?

 

My old boat would start to get really hot if I was running slalom speeds for any extended periods of time. I put a 140 thermostat in during the hot months and it helped.

[gregy]

My friend actually had a boat with a mercruiser I/o that had the thermostat installed backward. I remember him saying the cooling was weird.

[pkreusch]

@Waternut @gregy The tsat is installed correctly.

 

For today, I tested the tstat again and it tested fine. Opens at 160 deg's. Fully open at 185 per service manual testing procedures.

 

Tomorrow will probably have me pulling the engine recirc. pump to inspect. Maybe that will shed some light on the situation.

 

Here is the cooling diagram I promised.

Blue is cold water. Red is hot water after thermostat opens. Brown is recirculation water before and after thermostat opens. The tstat is in the upper portion of the tstat housing. The only path from the downstream side of the tstat is out through the manifolds. The path upstream of the tstat recirculates back to the engine circulation pump. It appears that there is no bypass hole in this system. It will purge the air from the system when the tstat opens, through the manifolds.

 

 

[pkreusch]

@DW Correction DW, on May 4th I quoted this " The housing directly short circuits the raw water to the manifold path AND to the engine circulation pump path." This is incorrect. The tstat housing downstream of the tstat ONLY goes to the manifolds. The raw water pump basically pumps cool water to the "circulation" path that incorporates the engine circulation pump and the engine block. This provides the "feedback" circuit that allows water to flow through the engine until it warms to operating temperature. After which, the tstat lets water out to the manifolds and is replaced by the raw water as needed.

 

I spoke to a local shop that had a similar symptom recently and the customer had a malfunctioning water recirculation pump. Seems I may have been on the right path but just didn't get there yet....Maybe tonight.....Stay tuned.

[DW]

A malfunctioning water circulation pump could certainly create the scenario you are seeing, from your circuit diagram the cold water from the raw water pump passes through the output side of the thermostat housing prior to entering the water circulation pump then to the engine block. If the circulation pump varies the flow or resistance it could create an engine temperature variation by pushing more or less water to the engine block. Good luck & make sure if a replacement is required you get a marine version since it appears your engine is open cooling & does not use antifreeze.

[pkreusch]

Update.... Circulation pump is fine. I am out of ideas... Local mercruiser mechanic says that the symptoms are not typical of a head gasket leak. He indicated I should see steam coming from the exhaust if its a head gasket. I'm pretty sure I haven't seen any steam in the exhaust. I'll check the block drains (on his suggestion) to make sure I don't have blockage in the block.

[Sethro]

The only thing I see you haven't checked is the exhaust hoses from the manifolds to the mufflers. I once had a Supra (Indmar Conversion) that had overheating issues. I tried many of the things you mentioned already, but found the baffles inside the exhaust hose had collapsed causing flow restriction, obviously. Didn't find the problem until I was standing on the dock and watched my dad take off and noticed no water coming out the port exhaust flapper.

[pkreusch]

@Sethro Thanks for the great suggestion! Unfortunately, the setup I have is the hard "S" pipe. It is an option for this motor from Mercruiser. There's a short rubber coupling (6" long) from the riser to the pipe, the "S" pipe, then another rubber coupling connecting to the muffler. Great thing is I never have to replace that traditional $75 per foot expensive exhaust hose. See attached image below. #14 is the optional pipe and #13 is the regular hose you mention. As I work my way around the rest of the boat, I still need to inspect the mufflers. I believe they are fiberglass so they may have come apart inside like Wish's boat's did last year.

 

[Waternut]

Usually when the mufflers start coming apart you get some power delivery issues but that's just my experience.

 

I still think you should try to run without a thermostat completely. Costs like $3 for a new gasket and if you're still running hot, you'll know that this issue lies deeper than the simplest of parts. Could be that a rubber impeller or some rusty shale has come apart in the past and finally lodged itself in one of the cooling jackets in the engine which isn't allowing enough flow. The only way to truly know that's the case is if you give it full flow through the thermostat housing.

[pkreusch]

@Waternut thanks! Will do. Stopped by one local shop to discuss symptoms and he agreed they don't really add up to head gasket. I have a few more items on my list to check which includes open tstat. P..

[thager]

If it worked last fall when you put it away bleed all your hoses. If water comes out move on to next. Won't cost you anything but 3 minutes of time. OK, I'm done.

[prk]

just fired up my 2002 gto22 with the black scorpion 330 for the first time this year crossed my fingers and turned the key seems to be working fine going to take a set this evening, been recovering from a cracked rib the past 3 weeks but the weather is to good to past up here in Vancouver hope you get yours running soon. go gekko

[pkreusch]

@prk thx. Nice to know there's another Gekko owner out there

[RAWSki]

Good Luck, I have a Scorpion 330 and it has been a good motor. The only time I had a cooling issue was when weeds starved my impeller of water and it disintegrated. I quickly replaced with a new spare I had but failed to check "down stream' of the raw water pump where pieces has lodged. Took about 10 minutes to overheat again and set off the alarm.

 

[oldjeep]

Typically when you shred the impeller all the bits wind up in the trans cooler

[pkreusch]

@thager Thanks for the insightful response. This issue came on slowly last year and for personal reasons we parked the boat for the winter season. I've never had to bleed the air from any of my 3 ski boats. This is an open cooling system, it bleeds itself. I'll try your suggestion anyway though.

@RAWSki I've had every downstream component apart now chasing this issue. Thanks for the suggestion.

@oldjeep When I first bought this boat 8 years ago, my pre-first-ride checklist had me cleaning bits out of just that. the previous owner just didn't take care of the boat very well. Fortunately I've never had to learn that lesson on my own boat. I always replace the impeller at the first of the year. The Scorpion 330 HP motor has been bulletproof for me as well.

[pkreusch]

Update....Today I put the water pump back together and reinstalled it. I cleaned the temperature sending unit with a wire wheel and tested it with the gauge in the boat to rule out both. See a pic below of the funky setup I used. I was able to verify the gauge and sender are good. I was able to hold the temp steady on the gauge for 10 minutes each without any deviation at 160, 180, and 200 degrees. Confirmed temperature at sender with IR thermometer. I used a small propane flame heat source (coming from right side of pic). I reassembled the tstat housing (sans tstat) and will be going to the river for a test in the a.m. Stay tuned...

 

 

[pkreusch]

Update..Couldn't get to the river on Sunday or today. Broke my fake-a-lake today. An aggravating few days... Hmmmmmph.

[pkreusch]

Update.. Ran without tstat today and the temp never got over 105 degrees. Ran for 5 minutes in neutral at 2000 RPM, then for 5 minutes at chug speed down the river where the boat plowed without getting on plane, then for 10 minutes at 3000 RPM (on plane), then back to the dock for about 7-8 minutes at 4000 rpm with 5500 max throttle at short 30 second bursts. IR thermometer indicated 108-110 degrees at the manifolds and 100-105 at the hoses. When I pulled the throttle back hard to neutral to stop and turn around, the temp never spiked.

 

Soooo.... What can I rule out? What does this test tell me? I assume I'm getting full flow through the cooling system.

 

Put a new tstat back in tonight and will river test on Friday or Sunday.

[gregy]

Mis-labeled tstat?

[pkreusch]

Possible... Not very probable. Tstat bench tested good 2X.

[pkreusch]

Update...You'll all be glad to know that the issue has been resolved, although the exact problem cannot be definitively diagnosed. This weekend, I purchased a new tstat (even though the old one tested good twice), water pump impeller even thought it was replaced last year in November and it looked good visually), and a pump body (even though I replaced it the same time as impeller). I checked/cleaned all electrical connections related to the circuit. Finally, I cleaned the temperature sender of a buildup of crud that may have been causing a slow reaction on the gauge. Since all these things happened at the same time it is difficult to tell what the issue was. Drove down the river for 45 minutes at 175 degrees... Perfect....

 

Thanks to all for your suggestions/comments. Another issue resolved. :)

[DW]

Glad it is fixed. You might want to check the old stat for a water bleed and (not that you want to open up the housing) try to recall if new stat had a bleed. Lots of other work could also have been the root cause.

[pkreusch]

@DW Thanks. No water bleed on either tsat. Triple checked replacement tstat part # to original parts list to ensure. Even had help from our local Mercruiser dealer here in town. The manifolds DO get cooling water from somewhere as it only takes 15 seconds to see water in the exhaust but I haven't any idea how. I had it all apart, looked and looked, but found no path. It's mystery to me. I have the old manifolds and they only get fed water from the elbow at the bottom of the manifold via the tstat housing. I searched that tstat housing 9 ways from Sunday and it only has 1 water path downstream from the tstat - that's out to the 2 manifolds. I'm forever bewildered....