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COboarder
06-26-2007, 02:45 AM
Hello Everyone,
First of all I would like to say thank you to everyone who has in the past, and continues to post so much useful information on this site. I have read through many of the posts and as a new boater I have learned a lot from your experience.
So here is my situation. Last Fall I purchased a 1994 Prostar 205 with the LT-1 engine, I am unsure of which transmission it has, it does have a mesh filter on the raw water intake. It passed a pre-purchase inspection at the local boat shop with flying colors. Taking it out on the lake, it ran perfectly, but then began to overheat. I quickly shut it down, let it cool, started it up, and with a quick acceleration the temp fell back to the normal range.
I took it back to the boat shop and they replaced the raw water impeller and the thermostat. The impeller was worn, with several missing fins and looked rather beat up. The next time on the lake, the same result. I noticed that the problem was worse at idle speeds, e.g. - picking up a fallen boarder, or just leaving the marina.
By reading several of the thorough postings on TeamTalk, I informed the boat shop that the LT-1 had two thermostats. They replaced both thermostats during the winterization process and it sat for six months. I took the boat out for a shakedown run in the spring and spent four days at Lake Powell with perfect and consistent engine temps. Hurray!
Then this weekend…the problem returned. Watching the temperature gauge, the engine temperature would fluctuate from 140-180 degrees up and down. Then it crept higher and higher. Once again, after cooling some, a quick acceleration and the temperature dropped back to normal. Needless to say, I am becoming a bit peeved and quite neurotic driving with one eye on the temperature gauge the whole time.
So here are my questions. 1) Do any other LT-1 owners have such fluctuations in the engine temps? 2) Barring a faulty thermostat (I understand this is a possibility) or a dead raw water impeller (I will check it tomorrow), what else should I check or have the LBS do? I am hoping to borrow a laser thermometer for this weekend to actually check the engine block temperatures if it has a repeat performance. Please keep in mind that at this point I know next to nothing about boats, and while not mechanically experienced, I am not afraid to learn. Thanks, Shawn

kbrum
06-26-2007, 06:31 AM
Possibly a piece of the old pump got into the new one and trashed it.

COboarder
06-26-2007, 02:02 PM
OK,
So I pulled the mesh filter and it had minimal detritus in the receptical. I checked the impeller and it appears fine. After replacing the impeller and cap, I ran the boat on the hose for several minutes while I was looking for leaks etc. Water was flowing out of the intake on the bottom of the hull before I turned the engine on, when the engine was running there was a lot of water coming out of both exhaust pipes. The temp climbed up to about 160 and then dropped to 120-140.
I shut it down for several minutes and then turned it back on to fiddle with the shower. Within a minute or so the temp climbed up to 180 degrees and then beyond. I shut it down promptly. I didn't have a way to check the physical temperature, but the engine didn't "feel" hot. Any ideas?

Oh, and I lost the brass cap for the hose adapter....where did that thing go. Crap!

tommcat
06-26-2007, 02:22 PM
if i remember correctly the t-stats are each different on the LT-1 and putting the wrong one in the wrong location can cause temp issues. since the boat shop wasnt even aware there were 2 t-stats i would check to make sure they are in the correct location.

SkySkiSpokane
06-26-2007, 07:48 PM
This is very interesting. I have just started having the same problem. I replaced the T-stats and the impellor just to cover all of the bases. I used the two different ones as advertised (140 & 160). I was pulling a wakeboarder the other day and looked down and the temp gauge said 210. :eek: I had no light, no beeps, and no engine shut down like you are supposed to get when that happens. I threw the engine box open and everything felt "normal" Manifolds where fairly cool to the touch and nothing seemed overly hot.

That was the first time it happed when I was under way. It happens at idle sometimes and I just put it in nuetral and give it 1500-2000 rpms for a second or two and it drops to the normal 140ish. I thought that maybe it just wasn't getting enough water at idle but it is still happening after changing all t-stats, gaskets, and impellor.

I have no fix for this but hopefully someone does (JimN). Just glad to see I am not alone.

tommcat
06-27-2007, 07:45 AM
what kind of impeller are you using? i used a blue one last year that was supposed to last longer and be able to run dry(which is true) but i found the vanes were too bendy(technical term) and at low RPM they just wouldnt pull water to the engine correctly. i always had to rev it up and then it was fine.

i switched to a stock impeller and everything was fine from there

ProTour X9
06-27-2007, 11:26 AM
This may not work at all, but we had a 190 with lt1 try driving fast utnil the temp goes down

Thrall
06-27-2007, 01:50 PM
One possibilty is that the temp sender is going bad.
LT-1 takes 2 tstats. Upper is a 160 deg w/ a small hole drilled in it (important part, right size hole, forget the theory behind it, something to do w/ low speed cooling maybe). The upper controls water to the engine. The lower tstat is a 140 deg, runs to the exhaust manifolds.
Only cooling issues I've had were when the raw water intake or the trans cooler got plugged, so can't help w/ this situation.

Jorski
06-27-2007, 04:21 PM
By the way, one thing to make sure of, is that you get the correct part from Mastercraft. Apparently, this t-stat is unique, you can't just use any 160 degree t-stat and drill a hole in it.

It is explained well here:

http://sstilletto.tripod.com/sstilletto/id11.html

COboarder
06-28-2007, 12:47 AM
Thanks for all of the posts!

Tommcat: I am not sure what type of impeller the shop put in for me. Is there a way to pull it and check? Are impellers stamped with some identification of how soft or rigid they are (durometer)?

ProTour X9 and SkySkiSpokane: When is has overheated in the past, I will allowed it cool a little and I have had some success with quickly accelerating to get up to speed. The higher RPM's, higher speed or both will sometimes cause it to drop right down to 140. And sometimes it will overheat at speed. My initial hypothesis last Fall was that the thermostat was old and the "extra" pressure at high speeds/RPM would allow it to pop open. The thermostats that are in now have six days on the lake. I would hope that they have not failed in that short of time, but I suppose it is possible.

Thrall and Jorski: I am hopeful that my shop put the proper thermostats in, and in the proper locations. Can you use a 160 degree thermostat such as this one ( http://www.skidim.com/prodinfo.asp?number=98-6034 )? This one from SkiDim does say that it is drilled, or does the part have to come directly from Mastercraft. If that is the case I likely do not have the proper thermostat.

Thrall: Sorry that I am a bit uneducated here, but how do you test to see if the sender is bad. If I do have the boat out this weekend I am hoping to check the engine block temp with something like this (http://www.infrared-usa.com/Product.aspx?ProductID=2270 ) if I can borrow one. Is there a better way? Just out of curiosity, what kind of problems did you have when the trans cooler was plugged? I seem to remember a thread that mentioned a plugged cooler on a boat without a strainer or due to impeller debris. The old impeller that was in my boat was definitely shredded.

Thanks for the input everyone!

SkySkiSpokane
06-28-2007, 01:03 AM
I purchased all parts from skidim. All parts were ordered by phone so I was sure I got the right stuff and not made the internet order mistake. I have the standard black impeller. My mastercraft dealer service reps(which will change on July 7th :woohoo: FINALLY) are a bunch of idiots. I trust skidim for all of my parts. I have also ordered stuff from Rambo Marine down south. I was having the same problems before and that is why I changed all of the cooling parts. Just having the same probs after the replacements. :confused:

Thrall
06-28-2007, 03:24 PM
[QUOTE=COboarder] The higher RPM's, higher speed or both will sometimes cause it to drop right down to 140. And sometimes it will overheat at speed.

If it's overheating randomly (or appears to be by the temp guage), then it's likely a bad top thermostat (top one cools the engine and this is the temp you're seein on the guage). Or debris somewhere that is getting hung up and restricting flow, some of the time.
Another possibility, however, I'm just specualting. There could be an air leak in the raw water line somewhere that makes the rw pump cavitiate sometimes???????

Thrall and Jorski: I am hopeful that my shop put the proper thermostats in, and in the proper locations. Can you use a 160 degree thermostat such as this one ( http://www.skidim.com/prodinfo.asp?number=98-6034 )? This one from SkiDim does say that it is drilled, or does the part have to come directly from Mastercraft. If that is the case I likely do not have the proper thermostat.

Yes you can use Skidim thermostats, they have the right stuff. You can actually use automotive tstats. I replaced both of mine a few years ago, preventative maint, and used Napa ones, just drilled the same hole in the new one as the old one had. Thrall: Sorry that I am a bit uneducated here, but how do you test to see if the sender is bad. If I do have the boat out this weekend I am hoping to check the engine block temp with something like this (http://www.infrared-usa.com/Product.aspx?ProductID=2270 ) if I can borrow one. Is there a better way? Just out of curiosity, what kind of problems did you have when the trans cooler was plugged? I seem to remember a thread that mentioned a plugged cooler on a boat without a strainer or due to impeller debris. The old impeller that was in my boat was definitely shredded.

I believe, don't know for sure, that the temp sender is just a resistor that changes resistance w/ temp change. I don't know what the specified values (ohms) are though. Sure wish I had a complete Indmar repair manual!
An ir thermometer will probably work, shooting the block near the temp sender (close to a water jacket there) and comparing #'s.
The temp sender, I'm pretty sure is inexpensive. Easiest way, get a new one at Napa, and eliminate it as a possibility. Take the old one w/ you b/c it's likely not the same as the Vette part.
When the trans cooler plugged, the engine heated up. Noticed it didn't drop down after restarting, was aroung 200 deg. Pulled a wad of seaweed out of it.
If your old impeller was shredded, likely, there's part of it in the engine somewhere. I didn't winterize my boat until I had it a couple years (skiing's good in AZ in Dec) and was suprised to get a bunch of old impeller parts out(not mine) when I drained the exhaust manifolds.
It's reccomended to try to blowout/wash out all water passages. Take hoses off, etc and go thru the cooling system in it's entirety. Haven't had to do that, sounds like pain, but.....

bowtie355
06-29-2007, 12:43 AM
I assume the new MC LT1 has a heat exchanger coolant set up. If this is the case this might be the problem:
When the LT1 in Corvette and Camaros have there coolant changed, the coolent system has to be purged of trapped air in the system or the engine will overheat. This is done by a Schader valve on the thermostate housing.

dh_bennison
06-29-2007, 08:52 AM
I had exactly the same problem, when I bought my LT1. It turned out to be a simple fix. Some of the fins on the Impellor were bent around the wrong way so they couldnt pull water through properly. From memory the impellor turns clockwise ( couple of the fins on my impellor were bent forward as though they should be going anticlockwise. I hope that make sense!!

COboarder
06-29-2007, 09:49 PM
I checked the impeller on Tuesday and it looks like it is all in good shape and fins facing the proper direction. Good idea however and something that would be a quick check if anyone has problems in the future.

Farmer Ted
06-29-2007, 10:42 PM
I had exactly the same problem, when I bought my LT1. It turned out to be a simple fix. Some of the fins on the Impellor were bent around the wrong way so they couldnt pull water through properly. From memory the impellor turns clockwise ( couple of the fins on my impellor were bent forward as though they should be going anticlockwise. I hope that make sense!!


I'll call Bull$hit, everytime the impeller rotates the fins go from being compressed on the right side to no compression on the left. If your fins were bent over the incorrect way, was your impeller rotating backwards?

Thrall
07-03-2007, 05:38 PM
I had exactly the same problem, when I bought my LT1. It turned out to be a simple fix. Some of the fins on the Impellor were bent around the wrong way so they couldnt pull water through properly. From memory the impellor turns clockwise ( couple of the fins on my impellor were bent forward as though they should be going anticlockwise. I hope that make sense!!

That's caused by the engine sometimes rotating backward part of a revolution when you shut it off (hit's the next compression stroke, but no power to turn thru it). It will bend the impeller fins backwards, but they straighten out as soon as they go back around once the right direction.

COboarder
07-06-2007, 08:18 PM
So I replaced a ruptured hot water supply hose on the shower today and ran the boat in the driveway to check for leaks. It was running on the water supply from the house and was picking up water. I ran it for several minutes and the temp climbed up to 160, 180...I turned it off when it got over 180. I didn't have an infrared thermometer, so just out of curiosity I (carefully) felt around the engine block. Yes it was hot, but I could safely touch all parts of the engine without getting burned. Somehow I doubt that I would be able to touch the heads and block if the temp was REALLY 180 degrees. Any opinions?

Farmer Ted
07-06-2007, 10:30 PM
when you told the dealer that winterized your boat that the LT1 has 2 thermostats, did you tell them that they are not the same?

I've got the Indmar manual and the only thing it says for overheating is to ensure your thermostat is operating correctly " A faulty new thermostat is a common occurence" page 348 bottom right paragraph

make sure the thermostat is installed in the correct direction

the only LT1 info in the book is "On 5.7L LT-1 Models, a special thermostat housing and recirculation pump are used to create a revers flow cooling system. On this model, water flows through the cylinder heads and thenthe cylinder block. This arrangement increases overall performance by lowering the cylinder head temperature compared to other models. The special thermostat housing contains two thermostats to offer a two stage cooling system that provides optimum control of the engine temperature."

Have you checked the indicating system? It indicates hot but is that accurate?

John B
07-06-2007, 10:51 PM
I have a friend with a 94 PS 190 with a LT1 that had the same problem as you.When it was first started in the morning it would heat up way to fast,it would hit 180+ when we would idle out of the 5 mph area.As soon as the motor's RPMs were brough up it would drop to 140(drop like a rock). Then it would run at 150, 180+ all the way to 200 and drop to140.It had new thermostats 160,and 143,and a new impeller. Well we put a new 160 thermostat in and that fixed it.It now runs at 160
New thermostats can be bad, I also have a LT1 in my boat(96 PS 190)and it runs at 160 with a heat stoke of 190 to 200