GT-40 Temperature Problem (or gauge problem)

[Verruckt32]

Not sure what happened, but here is the scenario (sorry, it's kind of long).

We were out on the water wake surfing and all of the sudden noticed that the temp gauge was pinned hot. We shut off the boat and looked around the engine and felt the risers and all of that stuff and it all felt fine. We swam under the boat to see if anything was caught in the raw water intake, and nothing was there. So we tore apart the water pump and pulled the impeller out. It looked ok (vanes a little bent) but since we had it out, we replaced it with our new spare. While we did this and the boat was off, the temperature gauge stayed pinned hot eventhough the boat was off (all the other gauges don't read anything when the boat is off, shouldn't the temp also?). Anyway, we started the boat up and let it idle for a bit and everything seemed fine, the risers felt just warm like they should so we emptied the ballast and cruised around for a bit and kept the hatch open to keep a hand on the risers as we went, and they stayed cool. All this time, the temp gauge never moved, it stayed pinned. We pulled the boat out and then we ordered a thermostat and replaced it. Once we did that, the temp gauge finally reset when we started the boat again and read 160, but we took it out to ride that weekend and the temp gauge will go from 160 immediately to pinned, then back sometimes and the gauge is just all over the place. It's not doing it slowly, like the water temp is actually changing, the gauge is showing 100 degree changes instantly. So anyway, I'm thinking that either the gauge itself is bad, or the water temp sender is bad. I can't think of anything else to replace. Thoughts???

[jchamlin]

RE: GT-40 Temperature Problem (or gauge problem)

I've had some inconsistencies with my temp gauge when my battery was not fully charged...but I've never seen it jump quickly. Sometimes the temp would read 170 or 180....but when the battery was fully charged, it seemed ok.

[15offbum]

RE: GT-40 Temperature Problem (or gauge problem)

I had a similar problem with my GT-40 two years ago. The temp guage was reading high but everything seemed fine. I replaced the thermostat but still had the problem. It eventually started falling into limp mode from time to time. It turned out to be a bad water temp switch. Once I replaced the switch, it was back to normal. Skidim.com has the part, I think it was about $30 and might be worth trying. You might want to call before ordering. There were a few on the website so I called to make sure I got the right one and the one I almost ordered online was not the right one for my engine. Definitely worth the call - those guys know their stuff.

[Verruckt32]

Thanks for the info. I think that is going to be my next course of action. I'll call SKIDIM and talk with them. They have a part that they call a water temp sending unit that is only $9. Is that the same part that you got. That is the only thing I see on the site.

[15offbum]

If you search "temp" on skidim's website, you'll see the sending units ($9) and the PCM Pro Tec temp switches ($30). I can't recall which one I needed for my '99 SN, I just remember that the descriptions on the website led me to one part, but the info I got on the phone (and the part I actually bought, which worked) turned out to be different. When you call, they might also have ideas about other possible causes. Good luck.

[bobchris]

well, the issue is either the gauge or the sending unit, plain and simple. I would have never changed the impellar and gone to all that hastle. Your hand on the manifolds should have told you that the guage wasn't reading right so what you should have been done was to diagnos if it's the sending unit or the guage its self.

Not sure on the newer models but on the older ones you could ground the lead to the sending unit and it pegged the gauge then it was the sending unit, mind you once the lead was disconnected it should have went to zero, or maybe I have it backwards, but just .02, also I believe you can check the resistance at the sending unit and you could tell that way too, sorry for not being a little more specific.

[my94sport]

Have you used the fresh water flushing system??? I had an overheating problem on my 94 proboss 2-3 months ago and it ended up being the fresh water flushing system value got stuck and did not allow enough water to flow through. Hope this helps

[JUST-IN-TIME]

to test sender and gauge
find the sender wire
turn on key
touch the sending wire to ground
gauge should read maxed
if not bad gauge
if it does read max bad sender

[hokiesax]

Thanks for the info! (i'm co-owner of this boat). We will be getting a new temp sender today, so we'll see how it goes.

However, last weekend we rode (yes, with temp gauge not working) and everything seemed fine for a while...but we were loaded down with 9 people plus 1500lbs ballast. At the end of the day, the red warning light in the center of the dash came on and then the engine started running like it was about to run out of gas (I guess this is "limp mode"?). I felt the risers and they were pretty warm, but they weren't "scorching hot" like a CC mechanic told me they would be if the engine was overheating (he said I wouldn't be able to hold my hand on the risers for more than a few seconds). I think the oil pressure was only slightly high, but not at the upper end of the gauge...maybe 60psi. I turned the engine off for a few minutes and then turned it back on and everything ran fine. I just drove the boat for another 15 minutes to get it back to the ramp. No lights.

Last night we put the boat in to work on the trailer, so we just drove it 5min to my dock. No lights on the way there, but when I turned the engine on (hours later) to bring it back to the ramp, the light came on within a few minutes. Again, the risers were pretty warm but not scorching. And there's no way the engine could have overheated that quick, right? If replacing the sender doesn't work, then is the "temp switch" the next course of action?

[hokiesax]

To clarify my question, I'm assuming that there is both a "temp sender" and a "temp switch," correct? Or does the GT-40 only have one or the other?

[hokiesax]

So I replaced the temp sender and nothing happened. The gauge is still pegged out on the high side. I took off the wires and touched them to ground and the gauge stayed pegged out. Does this mean that the gauge is bad? If its the gauge that is bad, then why did the red warning light go off and put the boat into "limp" mode? The risers were pretty warm, but not crazy hot. I realize it could be oil pressure triggering it, but that gauge works and stays in the 40-60psi range (which is ok, right?)

[hokiesax]

I just talked to Correct Craft and they suggested that I make sure the wire behind the gauge is not loose or being accidentally grounded. Apparently on the temp gauge, if you disconnect everything it should drop to 0, but if you ground it, then it will peg out at 240. I disconnected the wire to the temp sender and it stayed pegged at 240, so he thinks its being grounded somewhere.

The guy had to go look some stuff up, but he thought that low oil (pressure?) in the v-drive could cause the warning light to go on, so he said to check that oil level. I thought it was only engine oil pressure and high temp that would cause the light to go on and into limp mode.

[JUST-IN-TIME]

v-drive oil
low oil
water temp

will cause reduction mode

[hokiesax]

UPDATE

I spent a lot of time on the phone with Correct Craft last week and they were very helpful and spent a lot of time trying to help me, but couldn't actually tell me how to fix the problem. It was getting late on Friday, so they told me to call a mechanic they knew in California (I think his name was Mike?). Anyway, this guy knew exactly what was wrong - the oil pressure SWITCH and off the top of his head was able to tell me what color the wire was and where exactly to find it on the engine. Once disconnected, the light stays dimly lit, but does not go into limp mode. I had replaced my temp gauge by this point, so I was able to monitor oil pressure and engine temp. Apparently the center red light on the dash will go on when the oil pressure SWITCH or engine temp SWITCH, which is different from the oil pressure SENDER or engine temp SENDER. The SENDERs send the signals to the gauges. The SWITCHes are a backup system that turns on the light and shuts down (limp mode) the engine if the driver doesn't notice the gauges are reading abnormally. Anyway, the mechanic said I could just pull off the wire to the oil pressure switch and the engine would run just fine. I just have to closely monitor the gauges in case something happens.

If there is a problem with the V-drive oil, then the other red light (on the left side) will turn on and also go into limp mode.

At first I was surprised that Correct Craft didn't know how their boats work...but this boat is almost 10 years old and who would know how to fix it better than the mechanic who does it all the time?

[hokiesax]

Oh, and just to clarify...yes, the temperature gauge AND oil pressure SWITCH went bad within a very short time of each other. Hence the reason it was so confusing to find the problem (it was actually TWO problems).