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g-Dog
09-16-2013, 02:58 PM
The normal operating engine temp on my '02 LTR has always be 160. Last Saturday it climbed to 120 and then barely moved from there. It might have gone up to around 135-140 a couple of times...then back to 120. I'm assuming this is either the temp sender or the gauge, but I'm not really sure how to check either one. Or could there possibly be something else keeping the temp down? I've had the boat for 6 years and this is the first time I've ever seen this.

mustangtexas
09-16-2013, 03:03 PM
Thermostat may be stuck open.

g-Dog
09-16-2013, 03:26 PM
That makes sense now that I think about it. I originally was thinking if it was stuck open the temp should still climb somewhere close to 160, but I guess when 68 degree water is constantly running though it that would be kinda hard.

Anyone happen to know what the part number is? There's a few different ones on Skidim.

catamount
09-17-2013, 04:20 PM
This happened to me this year at the end of the season. At one point it wasn't even climbing over 110. After popping the thermostat cover, it turns out that chunks of rust were preventing the thermostat from fully closing. I cleaned it out and it's been working fine since. Unless your thermostat is old, I'd recommend just checking it out before ordering any parts. If something has propped it open, clean it out and put back together.

http://i.imgur.com/8QwR2Nu.jpg

thatsmrmastercraft
09-17-2013, 04:24 PM
You can put a thermostat in a pan of water with a thermometer and heat it up to see what temp the stat opens at.

bleedgreen
09-17-2013, 05:28 PM
I had a similar issue on my 97 prostar 205 this summer. I assumed it was the sending unit. I talked to a buddy who is a certified MC mechanic and he said he uses and infrared temp sensor and shoots the front of the heads and right around the sending unit to verify the temp gauge. I did that and it was really cold, matched the gauge. It had been several years since they(my motor has 2) had been replaced so I ordered new. When I opened it up there was a big piece of impeller stuck in the thermastat holding it open. A previous owner must have had an issue at one time and it just worked its way out of the motor.

Short answer - if you have a IR temp gauge shoot the heads for a running temp to rule out the gauge.

g-Dog
03-27-2014, 12:57 PM
Well, I installed a new thermostat and temp still goes to 120 and holds steady. I normally don't start replacings random parts...but I figured the boat is 12 years old and could use a new thermostat. I also replace the temp sensor since it was only $10. So now I don't know if I got a bad thermostat from the dealer...or a bad temp sensor...or everything is fine and the gauge is bad. Anyone know how to test the sensor to see if it's good? I don't really want to remove the thermostat and test it if I don't have to, and I don't have an IR temp sensor either. Also, it seams weird to me that the temp on the gauge always stops exactly at 120. Is 120 the new 160? :rolleyes:

JimN
03-27-2014, 01:44 PM
Well, I installed a new thermostat and temp still goes to 120 and holds steady. I normally don't start replacings random parts...but I figured the boat is 12 years old and could use a new thermostat. I also replace the temp sensor since it was only $10. So now I don't know if I got a bad thermostat from the dealer...or a bad temp sensor...or everything is fine and the gauge is bad. Anyone know how to text the sensor to see if it's good? I don't really want to remove the thermostat and test it if I don't have to, and I don't have an IR temp sensor either. Also, it seams weird to me that the temp on the gauge always stops exactly at 120. Is 120 the new 160? :rolleyes:

How old is your impeller?

g-Dog
03-27-2014, 01:51 PM
Impeller is brand new. I replace mine every year. I've never had pieces broken off the old one or debris caught in the transmision cooler inlet housing thingy. Everything is clean as a hound's tooth.

Vwrench
03-27-2014, 01:59 PM
I have a LTR it runs @ 160. Change the T-stat and the 2 gaskets, see what happens. If the impeller was bad it would get hotter. V

g-Dog
03-27-2014, 02:06 PM
Impeller, thermostat, and temp sensor are all brand new. I have heard of new t-stats being bad, but I would think that would be pretty rare.

thatsmrmastercraft
03-27-2014, 05:28 PM
Impeller, thermostat, and temp sensor are all brand new. I have heard of new t-stats being bad, but I would think that would be pretty rare.

Of all the thermostats that I have replaced, there have only been two that were bad from new. I still remember when they taught us at tech school that new doesn't mean good. It is worth the ten minutes to test a thermostat before installing it if you are doing your own work. Now, if I could only remember that before I install the darn thing.;)

g-Dog
03-27-2014, 05:37 PM
Do you know if there's a way to test the sensor? It's the 2-wire type.

g-Dog
03-27-2014, 06:01 PM
Here's a stupid question...are there 2 separate temp sensors, 1 for the gauge and 1 for the ECM?:confused::o

thatsmrmastercraft
03-27-2014, 06:31 PM
Not sure on either of those. Testing the sensor is just measuring resistance or voltage. Not sure how your boat is set up.

Rossterman
03-27-2014, 06:43 PM
IR gun is pretty cheap at harbor freight. Just saying..

Sydney Skier
03-27-2014, 06:49 PM
Guys Personally I think even 160 is still to cold. The big block in my spectra runs constant 180-190. No thermostat straight water pressure from an electric water pump and the water pick up under the boat. Smmer, Winter doesnt matter the season. 1 thing to consider in my opinion is there engine all be it marinised still have the same operating parameters as there automotive cousins. I have found through trial and error that all my small blocks i have built and the now the big block seem happier when they run a little hotter. They seem to be easier to tune and run and start better with my temp in the. You also need to remember that because these engines sit at big revs for long periods of time, operating temperautres are crucial. I have personally run the engine too cold on the odd accassion and 1 that springs to mind had a cold seize due to it running to cold. And our water temperautre gets down to around 12 - 15 degrees C. Just my 2c

snork
03-27-2014, 09:26 PM
what would be the ramification of running at 120 deg?

JimN
03-27-2014, 09:39 PM
Guys Personally I think even 160 is still to cold. The big block in my spectra runs constant 180-190. No thermostat straight water pressure from an electric water pump and the water pick up under the boat. Smmer, Winter doesnt matter the season. 1 thing to consider in my opinion is there engine all be it marinised still have the same operating parameters as there automotive cousins. I have found through trial and error that all my small blocks i have built and the now the big block seem happier when they run a little hotter. They seem to be easier to tune and run and start better with my temp in the. You also need to remember that because these engines sit at big revs for long periods of time, operating temperautres are crucial. I have personally run the engine too cold on the odd accassion and 1 that springs to mind had a cold seize due to it running to cold. And our water temperautre gets down to around 12 - 15 degrees C. Just my 2c

The main difference between a car and a boat is the lack of a radiator and Federal emissions mandates. The operating temperature of a car/truck can be maintained within a narrower range, too. Also, unless a car is raced, it's not running at WOT very often, so delivering a bit more fuel is a good way to avoid burning valves, pistons, etc. The frequent shut down of a boat makes temperature maintenance different, too.

JimN
03-27-2014, 09:41 PM
what would be the ramification of running at 120 deg?

A cold engine is not efficient. It requires more fuel to reach the proper air/fuel ratio, it doesn't burn completely and some of the unburned fuel ends up in the oil, which decreases lubricity/increases wear.

snork
03-27-2014, 09:58 PM
A cold engine is not efficient. It requires more fuel to reach the proper air/fuel ratio, it doesn't burn completely and some of the unburned fuel ends up in the oil, which decreases lubricity/increases wear.

What about a boat with cats, could ~120 deg temp still cause excessive fuel burn?

JimN
03-27-2014, 10:03 PM
What about a boat with cats, could ~120 deg temp still cause excessive fuel burn?


New engines aren't designed to operate with a 120 degree thermostat and Catalytic converters operate by burning off excess hydrocarbons through teh chemical reaction. This means that they'll fail due to the excess unburned fuel that reaches them.

snork
03-27-2014, 10:43 PM
Good to know Jim, thanks
Guess I need to check the thermostat

Sydney Skier
03-28-2014, 04:22 AM
The main difference between a car and a boat is the lack of a radiator and Federal emissions mandates. The operating temperature of a car/truck can be maintained within a narrower range, too. Also, unless a car is raced, it's not running at WOT very often, so delivering a bit more fuel is a good way to avoid burning valves, pistons, etc. The frequent shut down of a boat makes temperature maintenance different, too.

He said hes running a thermostat theoretically engine will still have a pressurising effect if the thermostat is closed. So then if that's the case how do you explain the closed circuit cooling system (heat exchanger)?

Thermostats to my understanding work exactly the same either in a car or a boat. Liquid temperature is relevant to engine revs in both automotive and marine applications. Thermostats use the same principles and open at the same rates relative to either car or boats liquid temperature.

More fuel is not always better. for a more consistent burn you require better engine volumetric efficiency/ IE a more efficient burn rate (slower burn and a bigger and longer production of energy forcing the piston back down the cylinder)

Constant stop start has the same effect on both engines. And if you think about it is probably harder on a ]n automotive engine as it s sits at idle for a fair chunk of its life stuck in traffic creating a huge heat soak into the engine bay and surrounding metallic materials. Boats however sit against I high density material that it insulated by water. Just my 2c

ricky365
04-02-2014, 12:10 PM
Whats part # of T stat and gaskets?