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View Full Version : LT-1 Thermostat question - JimN?


kpickett
04-28-2005, 02:27 PM
Two quick questions -

I changed out the thermostats on my '94 LT-1 this morning. It was running a little warm - not hot, but it seemed a little warmer than it should be. I got the new thermostats from my MC dealer, so I know I got the drilled 160.

Here are the questions - when I pulled the old thermostats out, they were both 160 degrees. The dealer gave me a 140 and a 160, and I'm pretty sure I've read that the lower should be 140. Is that the case? Is that also why it would have been running warm?

Also, there's no gasket on the upper thermostat housing, and I now get a very slight water leak out of it. I tightened it up pretty tight, and I don't want to strip the bolts out. Should there be a gasket up there?

Thanks so much for the help. I've learned an awful lot from this board.

Kyle

PornStar190
04-28-2005, 02:49 PM
Not really related to your thread, but RPM what does your LT1 Idle at when it's in neutral?

Thanks

PS190

NatesGr8
04-28-2005, 04:28 PM
the upper should have a rubber ring that wraps around the lip of the t stat, and the lower is lower temp thermostat.

What temp was your engine running at? I"m having the same problem right now of it running too hot. I'm around 178. I have changed both tstats, impeller, and backflushed just in case of any clogs, and still hot. My next plan of action is to check the circ pump and take apart the risers and manifolds to check for any good clogs.

erkoehler
04-28-2005, 05:00 PM
JimN, he is slacking today! But no matter when he shows up he will provide the solution.

kpickett
04-28-2005, 05:22 PM
the upper should have a rubber ring that wraps around the lip of the t stat, and the lower is lower temp thermostat.

What temp was your engine running at? I"m having the same problem right now of it running too hot. I'm around 178. I have changed both tstats, impeller, and backflushed just in case of any clogs, and still hot. My next plan of action is to check the circ pump and take apart the risers and manifolds to check for any good clogs.

Yeah, the upper does have the rubber ring. Strange that they had two 160 degree thermostats in there. I just took the boat out, and it runs cooler now. It was running around 170 or so. Now it's about 150 or so. It's hard to tell exactly on that analog guage.

I've been told that running hot can be a problem with the computer. I'm going to take mine in next week to have them check/update/recal the computer. You might check whether you're updated before you start tearing things apart.

My idle is aroun 650 or so.

NatesGr8
04-28-2005, 05:29 PM
update/recall????? i've heard no such thing.

kpickett
04-28-2005, 05:55 PM
Sorry - that's recalibrate, not recall.

PornStar190
04-28-2005, 06:23 PM
650 in neutral, I'm closer to 950 is there anyway to adjust the idle or is that controled by the ECM?

Tom Jones
04-28-2005, 07:45 PM
I was going to change the thermostats on my 94 LT1 this year because it was running cool (120). After talking to the local MC dealer they convinced me not to change them as the guages are not that reliable. They told me that unless I had black smoke scum on the back of the hull from unburned gas that it was probably running just fine. Mine idles at 650 also.

kpickett
04-29-2005, 02:23 AM
I was going to change the thermostats on my 94 LT1 this year because it was running cool (120). After talking to the local MC dealer they convinced me not to change them as the guages are not that reliable. They told me that unless I had black smoke scum on the back of the hull from unburned gas that it was probably running just fine. Mine idles at 650 also.

I always get a little black smoke scum on the back of my hull. Do you not get any at all? It wipes off easily when I wipe down the boat, but now you've got me worrying.

I figured that for $25, it was worth changing them out.

erkoehler
04-29-2005, 03:30 AM
Remember, if it ain't broke don't fix it!

Engine Nut
04-29-2005, 08:09 AM
Two quick questions -

I changed out the thermostats on my '94 LT-1 this morning. It was running a little warm - not hot, but it seemed a little warmer than it should be. I got the new thermostats from my MC dealer, so I know I got the drilled 160.

Here are the questions - when I pulled the old thermostats out, they were both 160 degrees. The dealer gave me a 140 and a 160, and I'm pretty sure I've read that the lower should be 140. Is that the case? Is that also why it would have been running warm?

Also, there's no gasket on the upper thermostat housing, and I now get a very slight water leak out of it. I tightened it up pretty tight, and I don't want to strip the bolts out. Should there be a gasket up there?

Thanks so much for the help. I've learned an awful lot from this board.

Kyle

The seal for the upper thermostat is Indmar P/N S556221. Your MC dealer should be able to get you one.

Engine Nut
04-29-2005, 08:16 AM
the upper should have a rubber ring that wraps around the lip of the t stat, and the lower is lower temp thermostat.

What temp was your engine running at? I"m having the same problem right now of it running too hot. I'm around 178. I have changed both tstats, impeller, and backflushed just in case of any clogs, and still hot. My next plan of action is to check the circ pump and take apart the risers and manifolds to check for any good clogs.

Are you sure it is really running that hot or is just the gauge indicating that temperature? The LT-1 has two tremperature reading devices. One for the temp gauge on the dash and one for the computer. It is not unusual for the two to be reading differently. I would trust the one that sends info the the computer as being right. Unfortunately, you will probably have to take it to a dealer and ghve them hook up their scan tool to get the reading.

kpickett
04-29-2005, 01:00 PM
The seal for the upper thermostat is Indmar P/N S556221. Your MC dealer should be able to get you one.

Is that the gasket for the housing or for the thermostat. I have the rubber seal around the thermostat. It's the housing that is leaking slightly. There was no gasket there when I took it off, so I wondered if there needs to be one.

Thanks for the suggestion.

Engine Nut
04-29-2005, 01:49 PM
There is no gasket for the 160 degree thermostsat, just the seal that goes around the thermostat. You might just have to replace the seal.

Thrall
04-29-2005, 04:50 PM
kpickett, yes, the 140 is the lower t-stat. Upper just has the seal around the thermostat.
Idle speed, on my LT-1 ('96) is 650-700rpms, except on a cold start it idles up to around 950-1000rpms and then idles down after 20-30 sec.
I am pretty sure the idle speed is ECM controlled, but check that the throttle body is not sticking open a little bit, maybe gummed up a little, if it opens up a little, your idle speed will go up.

Jorski
05-01-2005, 10:31 AM
Pornstar190,

Last year the throttle speed on my LT-1 was high, having increased all of a sudden. I found that a rubber tube (vacuum hose ?) located on top of the engine had slipped off of a metal tube that it should have been connected to (I figured this out solely because they were so close together). Upon slipping the hose over the open tube the RPM's fell right down to 600 or so.

I don't even know what this part does, maybe someone here can comment, but take a look.

JimN
05-01-2005, 11:19 AM
Pull the "metal tube" out and it should be a PCV valve. Same as on a car. When the rubber hose came off, it became a bad vacuum leak. Any vacuum leak behind the throttle plate will cause the idle to increase.

This PCV needs to be replaced during regular maintenance(annually).

sfitzgerald351
05-01-2005, 07:08 PM
Here's the hijack... will a bad/non functioning pcv valve or one that has slipped out of the block cause knocking under high load/heavy accleration and maybe an erratic idle? My 1992 Bronco has been knocking lately forcing me to run 89 or 92 octane and I can't figure out why. You'd think an EFI motor would correct, but who knows? I did notice the other day that the PCV valve was covered in oil and where the hose goes into the intake under the plenum (where you can't see) it was halfway out and loose.

What the heck does the PCV valve do anyway?

And does my 1984 have one? I do have a hose going from the valve cover to the flame arrestor. What is that for?

lakes Rick
05-01-2005, 07:28 PM
Your knock sensor has probably gone bad..... Call your dealer and see how many they sell for your year and model......

JimN
05-01-2005, 07:39 PM
The PCV ventilates the crankcase's combustible gasses and keeps them from mixing with the oil, breaking down its ability to form a film. If the PCV gets too dirty, the valve sticks and in that case, can affect idle because it's blocking the flow. If the hose cracks or comes off of the valve, the idle immediately raises because it goes into the manifold below the throttle plate. There's no way to control the RPM change from this. If the PCV valve comes out of the valve cover, it won't raise the RPM but it also won't draw the gasses in to be consumed.

An EFI will adjust only as much as it's programmed to. If you have detonation and it's not hot yet, try running some fuel system cleaner or something that gets rid of carbon deposits. If the motor has extremely high mileage, I would be checking compression, oil use and condition when changed and anything else that will indicate the health of the motor. The coolant temperature sensor can affect this, too. If it thinks the motor is really hot, it leans the fuel mixure and it can cause detonation on acceleration or under heavy load.

All of this is moot if there is a bad bearing or crack in the cylinder wall, though.

Ric
05-01-2005, 09:04 PM
Are you sure it is really running that hot or is just the gauge indicating that temperature? The LT-1 has two tremperature reading devices. One for the temp gauge on the dash and one for the computer. It is not unusual for the two to be reading differently. I would trust the one that sends info the the computer as being right. Unfortunately, you will probably have to take it to a dealer and ghve them hook up their scan tool to get the reading.
Larry can an average joe get an adapter to connect a scanner to the indmar pcm? My ski buddy is a ford tech and could probably look at the pcm if he could connect his scanner.
Further, what do you engine guys think of pcm tunes like the one from wester's garage? Is it a waste on a marine open loop motor or is it a question of what each user might ultimately want from his motor?

sfitzgerald351
05-01-2005, 09:28 PM
Your knock sensor has probably gone bad..... Call your dealer and see how many they sell for your year and model......

This is crazy, but from everything I've read and people have told me, the 1992 351 EFI motor in my Bronco doesn't have a knock sensor. Apparently it detects abnormal conditions through deciphering the conditions from all the other sensors.

sfitzgerald351
05-01-2005, 09:42 PM
And so I don't continue to hijack this thread... see

http://www.tmcowners.com/teamtalk/showthread.php?p=48177

sfitzgerald351
05-01-2005, 09:52 PM
The PCV ventilates the crankcase's combustible gasses and keeps them from mixing with the oil, breaking down its ability to form a film. If the PCV gets too dirty, the valve sticks and in that case, can affect idle because it's blocking the flow. If the hose cracks or comes off of the valve, the idle immediately raises because it goes into the manifold below the throttle plate. There's no way to control the RPM change from this. If the PCV valve comes out of the valve cover, it won't raise the RPM but it also won't draw the gasses in to be consumed.



Thanks for the explanation. Looking at my motor I don't see anything like a PCV valve, but I do have one hose going from the valve cover to carb below the throttle plates. I have another one coming from the other valve cover into the flame arrestor. Venting the crankcase makes sense, but why do the hoses go to separate spots from basically the same location on either set of valve covers?

JimN
05-01-2005, 10:35 PM
Look at the fitting that the hose is connected to, in the big grommet. That looks just like a PCV valve.

If Ford didn't advance the timing very much, it may never knock under normal conditions. However, I can't think of a way for any other sensor to detect knock. A knock sensor is basically a microphone that is tuned to the specific range of sounds produced during detonation.

I suspect that the one going to the flame arrestor is more for supplying a bit of fuel under load, when a little more gas is not a bad thing. Don't connect this one to the base, below the throttle plate. This is where you'll see the RPM go nuts because the PCV isn't there to limit how much air goes in. Also, if you were to put the left valve cover on the right side, I think it fits. This way, GM makes one part for both sides.

The hose from the PCV is a great place to spray fogging oil during winterization, though.

Tom Jones
05-03-2005, 07:32 PM
I don't get any black scum on the back of my boat.
The dealer advised me that if that happens and the temp. is running low the computer could be compensating for the low temp. by making it run a bit on the rich side. Since my temp. is showing a cool temp. but everything else seems fine, he thinks the gauage is just inaccurate.

JimN
05-03-2005, 09:54 PM
Remember that the sensor for the temperature gauge is not the same one that sends tempreature indication to the computer. Your gauge could read 0 and the ECM could still be getting the right info. I would have the dealer connect their diagnostic computer to see what the sensors are indicating. You may have an issue that the gauges don't show and the ECM won't throw a code.

Engine Nut
05-04-2005, 11:24 AM
Larry can an average joe get an adapter to connect a scanner to the indmar pcm? My ski buddy is a ford tech and could probably look at the pcm if he could connect his scanner.
Further, what do you engine guys think of pcm tunes like the one from wester's garage? Is it a waste on a marine open loop motor or is it a question of what each user might ultimately want from his motor?
You can buy an inexpensive scan tool from Rinda Technologies. Check out www.rinda.com they also have a real slick comouter program called Diacom that lets you use a laptop computer as a scan tool.

The marine ECM is not able to be upgraded with a chip like some automotive systems. Changing the Calibration requires the use of some very sophisticated computer software that is only available to the OEM engine manufacturers and a few select others.