LT-1 owners: There is a fix for cooling system issues

[gibbons]

I did that... that box is currently showing "Logged in" in green. If I wouldn't have registered as "gibbons", I couldn't have posted. It required all my personal info, etc. Is there a daily batch update that needs to come up before I show up as a member to everyone else?

[JimN]

JimN- Yup, moving the bleeders from the rears of the heads (where they work on cars) to the fronts of the heads. MasterCraft, Indmar, and GM Powertrain all missed that. I guess it's like you can't proof read your own documents effectively, it was obvious to me. It wasn't rocket science, but I caught it. The Service Bulleting was MC96-001, I have a copy that Nathan sent me when it came out. I will post the pics so everyone can check their LT-1's as soon as I am official.

OK, but the motor in the boats is at a different angle, too and that would make a big difference. The cars have a bleeder screw on the highest point of the cooling system and the boats can't have that luxury.

Stinkin' gravity!

Since that was the first bulletin of '96 (we had a binder with all of them), you probably came up with it in the middle of '95, right? I can't see them going out and acquiring data for normal performance in extremely cold weather, regardless of whether a few people were still boating. Cool, but not extremely cold but I know they could have done a custom program. Setting the fuel tables in extremely hot weather doesn't work well, either. There was one year Alan was pressured by someone (I don't remember if it was Indmar or MC) but they wanted the programs before they were ready and it resulted in cold start issues. Late '98, I think.

[Ski-me]

I have heard that once in awhile someone registers and it doesn't click all the way in. The new member can see he is logged in but for some reason, the posts still show up as "guest". Hopefully a moderator can check it out for you.....

And yes, I have an LT1 and know that it's reverse cooling and aluminum heads. I also would like to see what you have available. I'm also a Civil Engineer.

[gibbons]

OK, I will assume I am "in" and see if I can get pics to post. Attached (hopefully) is page 1 of the service bulletin. I messed around with the overheating during 95, got it zeroed in and submitted to MC in early 96.

In a car application, there is a tube that connects to a port on the rear of each head with big "banjo bolts". The tube hooks up to the cooling system to purge any bubbles that may get in the head. Once the bubbles in a car are gone, they're gone since it's a closed system. In the boat application, GM Powertrain and Indmar didn't think that one through, they left the tube on the back of the heads. Since the motor is at a large angle, and even larger when the boat is on plane, there is no way that bubbles can exit efficiently. They naturally float upwards and can fill the heads so water can't circulate. At higher RPMS, they can get scavenged out, but at lower speeds like wakeboarding, they can fill the heads. When that happens, there is no water cooling, and things get too hot really quickly. The bubbles get sucked into the cooling system through the hull intake when crossing frothy water, bouncing over rollers, etc. Heat soak can create bubbles when the engine temp goes over 212, so you can fill the heads with steam air when the motor is first turned off. Remember, car systems are pressurized up to 16psi and have antifreeze, which raises the coolant boiling point, so they don't have this problem.

The heads are symetric, they can be installed on either side of the engine. So they have port holes on the fronts and backs. The fronts, the best place to purge bubbles, have pipe plugs in them. I thought the rear porting was useless, so I removed the plugs and tube and swapped them front-to-back. The tube doesn't fit the front because of the water pump, so I spent quite a bit of time hand bending it to fit. But it can be done. The service bulletin page 2 has a list of threaded bushings, elbows, barbs, etc to pick up at a hardware store to do the job, but that would look cobby. They should have just said to bite the bullet and carefully bend the tube. Once the tube is hooked up to the front, take it to one of the exhaust manifolds like it was when in the back.

To make sure I wasn't introducing any bubbles into the system, I fabricated a bubble catcher from a soldered copper Tee, cap, and brass nipple. It installs before the thermostat housing. Any water entering into housing has to pass by, and the bubbles will rise into the cap and get purged into the other exhaust manifold. MasterCraft didn't see the need for that extra piece, but I did just for piece of mind.

After I did this, I never had another temperature spike with the accompanying RPM reduction. My temperature has been rock steady at 170 degrees. That's the topic of another post upcoming in this thread.

[mbpd312]

I give up!!

[gibbons]

I mentioned above that my motor runs 170 degrees steady. The next trick is to plumb the heater right. You gotta get the right source point and return point. This was devised by a guy a met, not me. He was crossing a lake in a bad storm, at a lower speed to keep his bow up. His heads filled with air, and his boat went into reduced RPM mode, which dropped his bow. He almost got swamped. He spent a lot of time with clear tubing on his cooling system to determine flows and what was needed. It works.

The right point for the source is in the circulation pump, cuz it has good pressure and the hottest water. You remove the Engine Coolant Temperature sensor from the pump housing, and install a Tee. The sensor goes back into the Tee, and a hose barb goes in the other leg as shown below. The return is into the port on top of the water pump, as shown in a picture in a post above. This works out great, because it keeps water flowing through the heater at any engine speed, and keeps water flowing consistantly past the ECT. If you do this, your heater will put out full heat at idle. Promise. It's great!

I like my motors to run a little hotter, they run these motors 220 in cars. 160 didn't "feel" intuitively right. I tried a 180, but that was too hot, I was getting too much heat soak when it turned off. It would go into reduce RPM mode. I needed a 170 degree stat. I like the Stant brand design, they seem more linear than the Robertshaw style that comes stock. I called Stant and drilled around until I got an engineer in the test lab. He actually made me 2 custom 170 stats. I installed one and keep the other for a future spare. Rats, that was years ago, I doubt I could repeat that event. I have scoped the Summit Racing and Jegs sites (muscle/race car guys) looking for an off the shelf 170, I don't believe one exists. If you ever see one, buy it for your newly plumbed LT-1.

[flya750]

A few notes:

flya750- if your boat is a '97, it probably as (better have) the cooling system changes incorporated from the factory. Hence, no cooling problems.

Gibbons,

I will check my '97 LT1.

Thanks for the heater fix info. I will look into it. The girls I ski with in the spring and fall will love the modification.

Welcome to the forum. I can't believe this is your first time visiting since you've been a MC nut for awhile now.

Anyway.. Welcome!

[Kevin@MWMC]

Welcome to the forum Gibbons, and here is the way to fix your account.

http://www.mastercraft.com/teamtalk/showthread.php?t=26931

Same thing happened to me when I first signed up......

[gibbons]

By the way, when (if) you winterize your boat, it's a good idea to back flush your heater. In the case of my set up, I remove the hose from the water pump and route it through the bilge hole (so the yuck goes right out). Then I connect a strong water pressure source to the return hose on top of the thermostat housing. Even running a sea water strainer, it's amazing the amount of junk that comes out. That includes rust scale from the engine block...

[TripleThreat]

gibbons,

There was some kind of issue when I registered also and at first I showed up as a guest. It all had something to do with some changes that were made to the forum a while back. If you send an email to this address and let Phil know you are having a problem, he will take care of getting it fixed for you.

[email protected]

Oh, welcome to the forum...

Jeff

edit... just noticed that Goliath pointed you to the thread with the contact info for Phil... Oh well...

[redlightning]

How does this apply to the 225 vrs? This motor is inverted. I have been trying to work out a heating problem all summer. I finally removed the t-stat to keep the motor cool until i figure out what is up. I notice the problem when i run the motor rpm's above 3200 rpm or so.

[captain planet]

I have been watching this thread and there are 2 things about which I am curious. First, my engine came with a 143 degree thermostat and runs at that temperature. Never had a problem with the lower temp, however my LT-1 isn't your typical LT-1 as it is rated at 350 HP because it is an Anniversary boat. Second, I have a heater and it does not run hot at idle, only at about 1000 rpms or so. Do you have any other pictures of where to replumb the heater? I don't use mine very often, however I had it on Saturday and going through a couple no-wake zones it cooled off.

[gibbons]

The 143 is the stat in the triangular "mixing" housing. It's job is to take motor warmed water and mix it with cold lake water, so there isn't so much of a thermal shock at the block's thermostat. The thermostat for the motor is under the aircleaner, under the filler neck. It should be 160 degrees. They used Robertshaw brand stock, I like Stants. That's the one that I got a custom 170 made, and it works great.

If your motor is running 143, that's too cold. The tolerances and clearances between components were designed for a higher temp, so everything has to thermal expand to fit right. That's the whole point behind "warming up" an engine. Plus will never burn off moisture and diluted fuel.

Back to heaters.... I'm not sure what my pictures aren't showing(?) The water comes out of the front of the circulation pump at the added Tee and returns at the nipple on the top of the pump. Ask questions....

And yes, I promise you will get full heat at idle. If you get the right temp range stat in there so it runs more like 160, all the better!

[Jorski]

CP,

Early LT-1's often had overheat issues. Sometimes owners (incorrectly) solved the probelm by removing the upper (163 degree) t-stat. That maybe the case with yours - it was with mine when I bought my 1993 used.

I would doubt that yours should be running at that cold of a temperature since the in cars they run at 180 degrees.

[flya750]

Gibbons...

You are Da Man! and a refreshing addition to this forum!!!

Keep the knowledge coming!!!!

THANKS!!