1995 Sport -- temp issues and surging...

scarbs wrote: Temp gauge stopped registering recently, so I took boat to local dealer for repair. I was initially told that thermostat was bad. After another week I was told that the thermostat was not bad, but was missing, and when they put the new one in, the engine temp was too high--approx 190 degrees. They are also telling me that the engine is surging, but I just got back from a 10-day Lake Powell trip and it ran perfectly the whole time. They have ruled out the gauge, sending unit, water pump, water strainer, suction pump, and blockage in the engine block. But even though they have not found the cause of the issue, they want to change the exhaust manifolds and risers claiming that even they don't appear to be leaking on the outside, they are likely leaking on the inside, and are likely the root cause of both the surging and overheating. This makes no sense to me. Does it make sense to anyone else?

I'd RUN from that dealer! They say it is surging but you haven't seen/felt it? What are they talking about?!!

You said the gauge was working until recently and then stopped. That tells me that the thermostat was there and working properly at the time. Then it is not registering (not getting hot enough), and they said the thermostat is missing? Where'd it go? Who took it out? The engine can't get to normal operating temp without a functioning thermostat, so how do they explain why it was previously at normal operating temperature without a thermostat? Then they put a new one in and now it is running hot?

While I don't know for sure, it sure sounds like they're don't have enough business and you're the perfect mark. They could have put a hot thermostat in to show that it is running hot so now needs more work. What temp thermostat did they put in? I don't remember what it is supposed to be on the GT40, but it is pretty low, like 142 or something like that. With that one, my gauge shows just under 160. I put a 160 in one time to see if my heater would be more efficient, and it ran on the gauge about 190 (I put the 142 back in because the GT40 needs to run cooler thermostats.

And what about the risers, etc.? Are they saying it is overheating because of internal leaks, or is that what is causing the surging (that you don't notice)? Many others on this forum know a lot more about the exhaust manifolds/risers, but mine were leaking externally quite a bit, and yet when I pulled them, I saw no evidence of leakage inside. If they are leaking inside, I would assume you would get some water into your cylinders, so you might be able to pull plugs and see if there is different discoloration. Can someone else on the forum speak to internal leakage, symptoms, evidence, etc.?

Anyway, can you please clarify what the problem(s) are that you are experiencing? Do you feel any surging? High temp (is it always this hot whether at idle or running hard (after warmed up of course))? I'd like to understand the problems you are experiencing, not what the dealer says you have.

Hold the phone!! Wait till Pete gets a-hold of this one.

A.) What engine are you running specifically? Carb'd or EFI?

Well, A.) is really how soon can you get your boat back from this dealer?

B.) What did your gauge typically read before all this happened?

C.) Check out Skidim's Overheat troubleshoot:
http://www.skidim.com/Faq_TROUBLESHOOT.asp#RWTS then Scroll down a bit, they have a separate little section for diagnosing the gauge.

It is an EFI GT-40. Usually ran around 150 degrees. I just called the dealer to get the boat back because I don't believe its line regarding the manifolds and risers. Dealer is now saying that the manifolds and risers are probably not causing the loping and overheat conditions, and don't appear to be leaking at the moment, but may need replacing in the near future. Fair enough. But still no diagnosis for the overheat and alleged surging. Like I said, it did not surge at all during my 10-day trip. Needless to say, I am very frustrated. I will check the Skidim link. Thanks for the tip!

I cant believe the dealer is getting an education on how to fix a simple project like this, all on your dime.

Based on your original post, it is pretty clear that the boat does not have a cooling system problem. Either a bad sender, bad gauge, or a mismatched pair... or a problem with the wiring between them. Pretty simple problem, which does not affect the functionality of the boat.

It is a 1995 Sport Nautique with EFI GT-40. Forgive my ignorance, but I am not sure what a smart pod dash is. But I was told that it has a separate sender for the gauge and the warning light in the middle of the dash. The warning light is not turning on when the gauge is reading 190.

Basically, like Mr. TRBenj said above, the actual engine does not appear to be overheating...something just seems to be causing the gauge to read the wrong temperature--likely a ground or other electrical problem like you described. But dealer has had the boat for three prime weeks and no diagnosis yet. And it hasn't even gotten to the loping/surging issue that it claims exists that I have never experienced.

Needless to say...I don't plan to go back to this dealer for my next issue. But I don't know of another marine mechanic that knows the GT-40 enginge very well.

scarbs wrote: It is a 1995 Sport Nautique with EFI GT-40. Forgive my ignorance, but I am not sure what a smart pod dash is...

The Smartpod is on the newer boats starting in 2000? or so, and involves more computer controlled wizadry.

I feel you are lucky you don't have it, it makes things a little simpler. Your setup should be similar to what most people on the site have.

Gentlemen--thanks for all of your help. Because of your input, I was able to sound reasonably intelligent when I talked to the dealer, which forced it to back off of its plan to change manifolds and risers and perform a compression test for the loping. I am supposed to hear from the dealer this morning and will raise the probable issue of bad ground at the sender. Hopefully I can get this issue resolved relatively quickly and get back on the lake with my sons.

You're right; it should have been done long ago (long before he told you to replace your manifolds and risers, which he later admitted was not the problem).

If it was me and I was confident the gauge and sender were okay, I'd run a separate test wire from the sender to the gauge. Start the engine with a hose, and watch the gauge while the engine warmed up (preferably with a 143 degree thermostat in place). You could also pull the sender, measure the resistance cold, then put the end in water, heat the water up (or just put the end in some hot water) to near boiling, and check resistance again (assuming someone has the resistance values). Actually better would be to hook up the gauge and do this so you could see what the gauge says (and measure the water temp with the infrared thermometer). Assuming the engine is okay (pretty sure it is), it can only be one of three things: bad gauge, bad sender, bad wiring.

This is all stuff I'd do at home; I would not want to tell this dealer (who should have already done all this stuff) to do it (and then charge you for it).

Hopefully this dealer at least knows the difference between a gauge temp sender and the EFI temp sender.

If you disconnected the EFI temp sender, it would probably do all sorts of weird stuff. Loping included?

scarbs wrote: I have no idea if I have an FCC.

I don't have a picture handy, but if you're looking at the engine from the front, it is a long black canister (about the diameter of an oil filter but much longer) to the right of the alternator (can't miss it). It has two hoses that come out of the top and head to the injector fuel rails, and a hose that elbows into the side near the top that comes from the low pressure fuel pump (mounted to the block below the FCC).

The FCC was added to lessen vapor lock.

Anyway, if you do experience surging/loping, I'd start a new thread on it. There are plenty of people on the forum can help you with that (if you ever experience it vs the dealer telling you you have a surge problem).

Good luck, and keep us updated with outcomes.

Hope they don't charge you!

With the thermostat out, if it says 130, then it's most probably the wire, the sender, or the gauge. I hope they put a 143 back in for you.

So, probably wiring. I'd run a wire directly from the sender to the gauge and start it to see what happens. Also, it could be some corrosion of the wiring (power). Your gauge will read wrong if the voltage is low. Boats around that timeframe are notorious for poor ground at the dash pod although that wouldn't be your problem. But maybe some corrosion on terminals, etc. Or a failing wire.

Too bad you're not local; should be easy enough to isolate it; just surprised the dealer couldn't (especially after all that run-around).

I believe the 160 is the correct thermostat for a GT-40 engine. The carbureted boats are supposed to have the 143. Not sure why the difference.

I agree with the possibility that the voltage to the dash is too low. I had to run a new ground and a new positive to my dash. I also added a new ground bus.

If you aren't getting enough hot air, tell us how the heater is plumbed. There have been some issues that have been resolved by adding a "Y" fitting.