PDA

View Full Version : LT1 overheating


Jorski
08-23-2004, 01:35 PM
I posted about my t-stats on the old board...but I am not convinced that all is well.

1993 LT1:

I have replaced the impellor and the t-stats. 143 degree in the bottom, 160 degree in the top, this t-stat came from skidim and has two holes drilled into it; it does not have a built in gasket. Both installed with pointy end out and pellet towards the block.

The symptoms:

Temp fluctuates wildly on the guage going from 140 to 220 and then to to 0 and back in a matter of seconds. I can hear the t-stat opening and closing repeatedly.

If I take out the top t-stat, and run with only the bottom one everything works fine, but a little cold. No wild guage fluctuations and no overheat/limp home mode.


My best guesses:

1) Heater (came w/ used boat) is hooked up incorrectly and this is somehow interfering with the water flow. Is this possible ?

2) T-stat is just not going to work if it is not the absolutely correct one from Indmar w/ the gasket. Hard to imagine, but maybe ?

3) The impellor and the t-stats are fine and the water pump is broken. The basis of this theory would be that when the upper t-stat is removed the restriction is reduced and the raw water pump and the circulating pump can provide enough water, but thaty once the upper t-stat is installed the increased restriction is to much for a failed circulating pump to over come !??

4) Anything else ?

While it seems okay when it is run with just the lower t-stat, I know that is not the correct set-up. Please any and all suggestions would be appreciated. Also any pictures showing cooling hoses and/or heater connections on an LT1 would be terrific.


Thanks,
Jordan

MYMC
08-23-2004, 02:02 PM
Have you bled all the air out of the system? LT-1s are extremely prone to getting air trapped in them. With the upper stat in and air trapped you get the condition you described. This would be where I would start.

JimN may have a few other ideas but this is why LT-1s installed in street cars had bleed screws all over them. :steering:

JimN, any thoughts?

Jorski
08-23-2004, 02:18 PM
What do you bleed ? Do you just open up the petcocks or do you remove any of the hoses ?

Thrall
08-23-2004, 02:48 PM
You have one of the earlier LT-1s. There was a thread on the old board I think mine "LT-1 Stalls After Ext Use" where Jim explained about modifications to the LT-1 cooling system, including the hole in the upper t-stat and bleeder/recirculating hose coming off of the heads, that remedied overheating problems on the lt-1s. See if you can find that, maybe your boat has not been updated.

Diesel
08-23-2004, 03:11 PM
2) T-stat is just not going to work if it is not the absolutely correct one from Indmar w/ the gasket. Hard to imagine, but maybe ?


This is your answer. When I did my water pump I had to go back with the Indmar stats. I tried every model the parts house had on the shelf and I could not find an off the shelf automotive model that would work. It had the same symptoms you are experiencing, open and close really fast with extremely high spikes. My guage was all over the place.

For the life of me I could not figure out what the difference was. In addition I could not get anyone to give me a good explination. The guy at the parts house said it would not work and he was right. I put in a new set of stats from the MC dealer and it worked perfectly..........

Hope it helps.

Diesel
08-23-2004, 03:17 PM
Have you bled all the air out of the system? LT-1s are extremely prone to getting air trapped in them. With the upper stat in and air trapped you get the condition you described. This would be where I would start.

JimN may have a few other ideas but this is why LT-1s installed in street cars had bleed screws all over them. :steering:

JimN, any thoughts?

The bleeder screw was there to remove trapped air in the system (in cars) since the radiator cap was not the highest point in the system and could not self-bleed like most systems. Since we do not have a closed cooling system it is not be possible for air pocket to form. If this occured the system would have to be bled every time the boat was put in the lake.

JimN
08-23-2004, 06:31 PM
Have you removed the bleeder hoses at the top of the motor and looked for any restrictions? Remove them and make sure they and the brass fittings are free of blockage. You may have some rust scale stuck in one or both of the lines. You may want to check the circulating pump to make sure it's A) the right one and B) working properly. The housing gasket should be available and it's worth knowing if that's the culprit. It could be worn and not moving enough water.

Did you look through the oil cooler to see if anything was stuck in the small tubes that the water flows through?

MYMC
08-23-2004, 06:46 PM
My apologies, I thought I read that there was closed cooling involved. You are correct that this should not be an issue with a raw water cooled boat. :confused:

We have seen this issue many times on closed cooled boats.

Sorry...

JimN
08-23-2004, 09:33 PM
The high temp at idle with raw water cooling is somewhat common, but goes away when the RPM's are higher. Especially on the earlier LT-1 boats with the bleeders at the rear of the heads. (kinda defeated the purpose)

MYMC
08-24-2004, 08:42 AM
We had a customer recently melt one of these to the ground...the steel coolant transfer line was plugged (rust and debris). He was in the intercoastal and needed to make it to shore...thought it would be okay.

The repair cost of one of these is staggering!

JimN
08-24-2004, 08:54 AM
I know the heads were around $1500 each a few years ago, but how bad was the rest of the motor?

Jorski
08-24-2004, 09:02 AM
Thanks guys, I really appreciate the help.

Jim when you speak of the bleaders, do you mean the small diameter rubber hoses that run between the exhaust headers and the the front of the engine ? Also, does anyone know where one can get a service manual or schematics for an LT1 ?

Thanks again guys.

JimN
08-24-2004, 09:28 AM
Those are the bleeders. Don't know where you could get the marine manual, unless your dealer has one they would want to part with or get for you. They're not cheap, though.

Jorski
08-30-2004, 03:52 PM
Quick update:

I replaced both t-stats with ones from a Mastercraft dealer..they for some reason did work better than the ones from SKIDIM (Thanks Diesle). It appears that the root of the problem, or at least part of it, was the heater. Once I shut off the valve that feeds water to the heater the boat was running at the correct temperature (160) consistently.

It appears that I now have everything running properly as it was when it was new.

So now, the only problem is that it does have the heat soak issue that it gets too warm when the boat stops after pulling a skier, engine management system cuts in, when the guage is reading only 180 degrees or more. It will cool down if I rev it in neutral.

In some earlier posts, it was mentioned that there was a MC service bulletin put out to correct this problem. It involved rerouting the bleeder that goes into the rear of the engine and drilling and tapping into the front of the head, so that cooling water stops the engine management system from thinking it is too hot.

Currently, the passenger side bleeder runs between the upper t-stat housing to the passenger side exhaust header and the other one runs between the driver's side exhaust header and the same side of the rear of the engine.

Is there anywhere that I can get a copy of the bulletin or does anyone know exactly where this has to go ?

Thrall
08-30-2004, 04:01 PM
I will look at my boat tonight if you don't get it figured out by then and tell you where all the lines run.
I don't know if there was an ECM cal update with the rerouting of the bleeder lines and hole in the tstat update.
Jim?

JimN
08-30-2004, 04:07 PM
There was a recal for high temperature climate users. I never heard that it was really necessary in other parts of the country. You can turn the bilge blower on and get rid of the hot air, too.

Diesel
08-31-2004, 10:00 AM
I replaced both t-stats with ones from a Mastercraft dealer..they for some reason did work better than the ones from SKIDIM (Thanks Diesel).

Glad I could help!!! I still have no idea why there is a difference in the stats :confused: .

I am not sure why you are having the heat soak issue. My LT1 is a 95 model so evidently something was changed because I have never had the issue you described. Hopefully someone else will have the answer.


Good Luck!!

Jorski
08-31-2004, 10:50 AM
Hi Diesel,

Any chance you could post a picture showing the bleeders ? Apparently they changed the location to dump some cooler water near the temp. sensor. It appears that the sensor is giving false overheat signals, causing the engine management system to go into limp home mode. Yours probably came with the new set-up. My year (1993 LT1) was one of the first ones out there.

BTW...if anyone else could post a picture...that also would be greatly appreciated.

Jordan

Diesel
08-31-2004, 11:00 AM
I'll will snap a few pics tonight but I don't have a picture hosing site. PM me you email and I will send them directly to you.

Jorski
09-01-2004, 09:39 AM
Thanks diesel...my email address is in your inbox

greeneng
09-01-2004, 09:30 PM
I have read this a few times, but just caught on that you said the replacement 160 Degree thermostat did not have a built in gasket.
Did you remove the gasket, actually a seal around the circumference of the thermostat, from the old thermostat and put it on the new one? If you do not have the gasket, you need to get one and put it in. When I ordered an LT-1 thermostat from Ski-Dim, in July, it came with the seal (gasket).

Diesel
09-02-2004, 09:46 AM
Here you go:

http://img50.exs.cx/img50/2541/DSC1164.jpg

Diesel
09-02-2004, 09:49 AM
Another:

http://img50.exs.cx/img50/7082/DSC1163.jpg

Jorski
09-02-2004, 11:36 AM
Thank you Diesel...Your driver side bleeder goes into the heads at the front near the temp sensor...mine goes into the back. That seems to be consistent with the "fix" I have heard about.

I am still somewhat unclear about what to do about this. I have heard that there was a service bulletin, anyone know where or if an individual could get a copy of this ?

Ther are not any MC dealers within a convenient driving distance and if possible I would prefer to do it myself. It sounds like all that is required is to cap off the old hole. Then drill and tap (in the correct spot-yikes) to insert a threaded hose barb into the cooling passage and then connect the bleeder.

Any ideas would be great.

Thanks again guys,

Jordan

Jorski
09-07-2004, 10:11 AM
Greeneng,

You were correct, you have to have the gasket ! In summation, LT1s must have t-stats from Mastercraft. Upper one drilled and installed with gasket.

Finally..the end to this thread. Thank you to all of you. This site has been a wonderful guide.

Cheers,

Jordan