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gibbons 08-01-2009 01:57 AM

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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 08-01-2009 03:12 AM


Originally Posted by gibbons (Post 619966)
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.


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!

[email protected] 08-01-2009 03:51 AM

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

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

gibbons 08-02-2009 03:21 PM

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 08-02-2009 03:55 PM


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...


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

redlightning 08-10-2009 12:47 AM

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 08-10-2009 10:03 AM

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 08-10-2009 07:29 PM

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 08-10-2009 10:00 PM


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 08-10-2009 11:01 PM


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

Keep the knowledge coming!!!!


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