View Full Version : Gauges giving some wierd readings

09-14-2012, 10:11 AM
So I am going on one month with my 91' MC Tristar...been able to get it in the water 3 times so far. I am however enjoying playing with it in the driveway which leads me to this post. When I fire it up on the trailer and let it run for a few minutes my gauges read as follows; RPM 800 or so, Oil pressure 30 & bouncy, temp 110-120 at most, volt meter 12-13. The boat starts almost always at the first turn of the key...underway @ 3000-3400 rpms speed is good runs around 36 mph @ 3400 rpm volt meter goes up to around 14, oil pressure stays at around 30 or so but the temp never reads above 120 or so. I actually took my wife's meat thermometer and measured the temp of the water coming from the exhaust (in the driveway of course) and it read the same as the temp gauge. Not sure if that's meaningful or not. Anyhow I wanted to toss it out there and see what others might think about this. I appreciate any feedback. I find myself wishin' I was just a little more mechanical when it comes to this boat but I have always wanted an inboard and will learn what I need to to keep this baby running so this is a great site for folks like me!

09-14-2012, 10:33 AM
This time of year I would think that the hose-water temp would be more than 120 there.:rolleyes: Seriously, the previous owner probably removed the thermostat. Even without the stat in on my boat at the moment, I can hit 150-160 idling in the driveway. Checking the stat is the first place to go.

09-14-2012, 10:39 AM
Is the thermostat fairly easy to find & get to?

09-14-2012, 10:54 AM
Nothing to it. Right at the front of the engine. Should look something like this.

09-14-2012, 11:03 AM
So when I take the housing apart it might just be an empty space underneath? Oh and me doing this brings to mind a saying about a monkey and a football...is there any way for me to totally screw things up taking this apart?

09-14-2012, 11:21 AM
Anything on a boat has potential to get screwed up, but this is relatively easy. In the picture, you see the thermostat in the housing. If you don't see it.........it's not there. BEFORE you take it apart, have a new gasket and some automotive silicone sealant to apply to the gasket fore-assembly.

Possible things that could go wrong:
Wrong thermostat
Thermostat in up-side down
Over-tighten and crack thermostat housing
Not center thermostat in housing

Pretty simple procedure to unbolt housing, clean both sides of housing, replace thermostat, apply a little silicone to gasket, replace gasket and tighten housing.

09-14-2012, 11:35 AM
I sure do appreciate all the help! Hopefully just one more question...is there a NAPA thermosat equivalent or do I need the official marine part? Thanks again for the input!

09-14-2012, 12:40 PM
I don't have the Napa number handy but the Sierra number is 18-3671. Someone should post that Napa number before long.

09-19-2012, 02:45 PM
Installed thermostat today...there was none when I opened housing. Got everything hooked-up and started engine in the driveway...quickly ran up to 155-160 degrees and stayed there. I am wondering if this is more like it and what to expect on the water.

09-19-2012, 02:56 PM
Yes that is the normal operating temp for your boat. Glad you got it figured out.

09-19-2012, 02:58 PM
160 is about perfect. You'll get better performance and fuel economy running 160 over running at 120. Lower temperature is not always better. See, working on these things isn't that hard. Soon you'll be tackling bigger things. Happy you got it working right.
Your voltmeter and oil pressure readings are about right. Not sure why it bounces at idle.

09-19-2012, 04:22 PM
Man this is a great site! Thanks for the feedback. But check this out...I get my new stat installed run the engine for 5-10 minutes or so and now it wont shut off had to disconnect at distributor. Now it's as if the key is turned on all gauges powered up, hour meter running, etc with out the key even in ignition. I've disconnected the battery and I am thinking I will next learn how to change an ignition switch and this boat has original key!!

09-19-2012, 04:35 PM
Perhaps your engine is just so much happier running at the proper temp it didn't want to stop? Seriously, you are probably on the right track with a new ignition switch. A fair bet to throw that in as it's cheap and you will need a new one sooner or later.

10-18-2012, 08:17 AM
So I got the stat problem taken care of...replaced the ignition switch...had throttle adjusted...gave my boat lot's of tlc while waiting to get her back on the water....put some marine gas in the tank and launched yesterday for a test run. Not good. After a good start engine began running really rough rpms would not exceed 2000-2500 engine nearly stalled in a turn. We limped around for a bit at idle and after a while the engine seemed to straighten out so we accelarated rpms went to almost 3000 but after a few seconds engine began running badly. At that point we concluded test run and came home to cry in our beer. Does anyone know a good Mastercraft mechanic in SE Georgia / NE Florida?

10-18-2012, 08:30 AM
The water coming from the exhaust isn't going to be boiling hot- some of hte water going through the cooling system bypasses the engine so it can cool the exhaust gases.

When you change the ignition switch, remove only one wire at a time or label the wires.

10-18-2012, 10:10 AM
Yep, I wired mine wrong once so that there was no accessory position, only on all the time and hour meter was running. Only had it out on one trip though before correcting the problem.