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  #51  
Old 08-12-2009, 09:33 PM
gibbons
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I will beat a dead horse.. if you re-route your heater as shown in my picture, you will get full, hot heat at 650 rpm. It's the only way we survived years of skiing in the spring and fall with air temps in the 30's and 40's. I have ridden a wakeboard while it was snowing...

Anyway, that pdf shows the stock plumbing configuration. Note the "bleed tube"... that doesn't work that well with a boat. The hole is offset to the back, and the hole if the fitting is pretty tiny to catch a big bubble. That's why I capped mine off, and fabricated that big Tee with the bleed tube on top of it. I am pretty sure I am catching all the bubbles with that unit.

Even if your cooling system is working right, you will get heat soak spikes. That happens with any engine, the big block in my Chevelle runs 195 but soaks to 230 when shut off. My LT-1 goes to 100 or so, but I am running it a 170. No problem, I am below the level that the ECM freaks out. What my head plumbing gig does is keep the heads from filling with air so they spike while running.
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  #52  
Old 08-17-2009, 02:56 PM
Jorski Jorski is offline
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Boat: 1993 190 with LT1
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Hey Gibbons,

Thank you for pointiong all of this out.

Turns out my crossover tube is on the back of my block. So, I am going to try and reconfigure things this weekend.

Is there any kind O-ring or gasket under the banjo bolts? Or does it seal in the threads?
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  #53  
Old 08-21-2009, 06:52 PM
redlightning redlightning is offline
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Boat: 1994 Mastercraft 225VRS LT1
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Gibbons,

Any chance you could post the entire TSB? I would like to see the parts list if you have it.

Thanks
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  #54  
Old 08-24-2009, 02:12 AM
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gibbons gibbons is offline
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Sorry, been gone playing with the Chevelle and bikes for a while.... I will see if I have the subsequent pages to the bulletin. It was just a bunch of bushings, barbs, and stuff like that. It's intuitive if you look at the situation. Banjo bolts have recessed o-rings in them that self seal.
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  #55  
Old 08-25-2009, 02:25 AM
redlightning redlightning is offline
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Boat: 1994 Mastercraft 225VRS LT1
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I made the swap. I ordered a new crossover tube from GM dealer. A little bending and it fits just fine. Pretty long tube, so i cut it off about 6 in from the fitting. I tied it into the drivers side exhaust manifold and swapped the hose coming from the t-stat housing over to the pass side exhaust manifold.

I do believe that this has made a difference. Temp is much more stable. I am still seeing a rise in temp when i run 3200+ rpm for 10 - 15 min steady. It creaps very very slowly up. Now does not seem to go past 185. This is the only time i see a temp issue. I can pull skiers and wakeboarders all day, starting and stopping.

Once it heats up to 185, it does not come down just slowing down to 2k rpm. It takes it a bit to start cooling down, even in neutral reving the motor a bit.

I have replaced the raw water impeller, hoses and t-stats. Looked for blockage in the system with no luck. The only things i have not replaced are the circulation pump, the molded hoses and the temp sensor. It does not seem to be erratic enough to be a temp sensor. Circulation pump? Could i have a hose collapsing? Any Ideas?
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  #56  
Old 08-25-2009, 08:48 PM
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gibbons gibbons is offline
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What value of thermostats did you put in? 185 sounds quite high, especially if you used a 160 in the circulation pump (on the motor). My custom 170 stats give me 170, when I tried a 180, I got about 185. That was too high, it allowed it to heat soak high enough to cause reduced RPM function.

The stock thermostats were Robertshaw brand, they look like they have a big brass cup off of the bottom. As I mentioned, I like Stant Superstats. They are stainless steel, and have larger stronger "thermal motors" and return springs. I went through all kinds of feel-good testing, and found the stove top test to be quite revealing. The Robertshaw seemed quite notchy in operation, and seemed like it wanted to search for an all or nothing opening operation. Stants open quite smoothly and very linear. I think they contribute to temperature stability.

Another thing that leads to stability is re-routing the heater lines like I my pictures showed. I'm not so sure the mixing stat does a great job as configured on an LT-1, I get plenty cool water into the top Tstat housing. Rerouting the heater lines as shown puts hot water back into the circulation pump and seems to stabilize the temp more, vs having such a temperature gradient between the hose into the Tstat housing and the circulation pump.

The circulation pumps are quite robust, but it could be that, I guess. There's nothing marine magic about them, you don't need an Indmar or even a GM. I would look for an Edlebrock or something like that to save money.
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  #57  
Old 08-25-2009, 10:41 PM
redlightning redlightning is offline
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The temp is acutally stable till running at higher rpm for several minutes.
150-160 is stable. The temp creeps up very slowly.

I have purchased 5 tstats. from 2 different mastercraft dealers as well as Skidim.

the motor has never gone into limp mode.

I actually removed the heater connections for now until i get this resolved. Not sure if i will reinstall it. We just dont use it.

I think the temp sensor is in the drivers side head. I think i will replace it next and see what happens. I wish i had a MC mechanic i could have look at it that i trust.
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  #58  
Old 09-29-2009, 10:12 AM
Lev24
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Cooling issue inquiry

I have a 1998 Prostar w/ the LT1 motor w/ about 450 hours. It is going into Norhtstar shut down mode after about 10 mins of operation. This problem just started out of nowhere about 2 weeks ago. I have...1) Cleaned the transmission cooler screen. 2) Checked the impeller which is new last year and working fine. 3) Changed the thermostat. 4) removed the water pump and flushed it and the ports into the heads with both water and compressed air. Boat runs fine out of water but the strange thing is that the water coming out the exhaust is cool. It is not steaming at all. It's like the water is not gettting through the heads. Any ideas?

Thanks!

Lev24
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  #59  
Old 09-29-2009, 10:28 AM
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JimN JimN is offline
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Quote:
Originally Posted by Lev24 View Post
I have a 1998 Prostar w/ the LT1 motor w/ about 450 hours. It is going into Norhtstar shut down mode after about 10 mins of operation. This problem just started out of nowhere about 2 weeks ago. I have...1) Cleaned the transmission cooler screen. 2) Checked the impeller which is new last year and working fine. 3) Changed the thermostat. 4) removed the water pump and flushed it and the ports into the heads with both water and compressed air. Boat runs fine out of water but the strange thing is that the water coming out the exhaust is cool. It is not steaming at all. It's like the water is not gettting through the heads. Any ideas?

Thanks!

Lev24
Check the ECT (Engine Coolant Temperature) sensor. It's the two-wire sensor with one yellow and one black wire. Use a multi-meter set to Ohms. If the resistance at ambient temperature is lower than what's in the chart I posted several times, it's bad. To test it further, remove the sensor, measure the resistance at ambient temperature and put it in hot water of a known temperature. Using the chart, compare the resistance at the higher temperature(s) with the chart. If it's not close, replace it.

If you're idling for a long time, occasionally put it in neutral and rev it up. If that doesn't help, clear out the bleeder lines from the heads to the intake manifold.

You also posted that you "changed the thermostat". Your motor has two of them. If you only changed the one in the normal thermostat housing, you missed the one behind the water circulating pump.

BTW- it's not a Northstar RPM reduction. This happens even with the motors that use a distributor.
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  #60  
Old 03-22-2012, 10:53 PM
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Jerseydave Jerseydave is offline
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Boat: 2005 X-STAR & 1993 Prostar 190 Limited
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Ok so I just purchased this '93 with an LT-1 and have not really run it much yet. (just a water test with the old owner)

I was going to install a new crossover tube on the front of the engine, but the alternator and bracket are blocking the right side cylinder head so it can't be done. I could remove the pipe plug on the left cyl head, but it seems pretty tight.

The previous owner didn't say he had any problems with it overheating, so I will try running it as is this spring and see what I've got.

Any other suggestions?

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