Need temp gauge help.

[ryan_289]

Ive got a new to me 98 chaparral 180le. We have had it out a couple of times and both times the temp gauge never got up above 120. (which is the bottom of the gauge). It is a teleflex gauge. I think the gauge is good, I removed the sending unit wire yesterday and grounded it out and the gauge went all the way to hot. If the thermostat was stuck open/removed would the engine stay at this low of a temp or do I have a bad sending unit? I thought I would just replace the sending unit to be sure but I cant figure out which one I need? The engine is a 4.3 Volvo Penta.

 

[Silvertip]

Re: Need temp gauge help.

Why replace a part when you don't know whether it's good or not. Measure its resistance. 33 ohms hot, 240 ohms cold and at ambient temperature it would be close to the 180 - 240 ohm range or so depending on how warm it is in your area when the measurement is made. Yes, no thermostat or one that is stuck open makes an engine run cold. That's why the engine has a thermostat. Check to see if you have one. If it is present, check its operation by suspending it in a pan of water on the stove. Note the word SUSPEND. The stat should open at its rated temperature. If it is open when you remove it just install a new one as that one is toast. Your approach to this is called "shotgunning". Throwing parts at a problem hoping you hit the problem is expensive, time consuming and wasteful.

 

[ryan_289]

Re: Need temp gauge help.

Thanks for the info. Will I need to replace a gasket on the thermostat housing or will it be an oring seal? How do I measure the ohms on the sending unit?

 

[Silvertip]

Re: Need temp gauge help.

You need a multi-tester (volt/ohm/milliammeter) available at Radio Shack or any home improvement store for about $15.00. If you plan to do any maintenance on your boat yourself -- especially electrical work, you need such a meter. Learn how to use it and it will save you a bunch of time, frustration, and expense. Remember, you can't see electricity. Broken parts you can see. Bad electrical parts must be tested and the vast majority of them as well the majority of electrical issues can be isolated and diagnosed with this meter.

 

[ryan_289]

Re: Need temp gauge help.

I guess I wasnt thinking. Ive got a multi meter at home. Ive only ever used it for volts. We are going to take it out on Sunday, I will check it before we leave and take a few readings during the day. Ill post back.

 

[Silvertip]

Re: Need temp gauge help.

When you make resistance (ohms) tests, the circuit must NOT have power on it and it must be disconnected from all other circuits or you get parallel or series readings that will be misleading. You want to measure the device only. That means the wires need to be disconnected from the sender.

 

[ryan_289]

Re: Need temp gauge help.

Woops. I wish I had read that this morning. I took readings but the wire was still hooked up. I can probably run out now and take a reading. It should still be warm. I got a 134 reading after riding just a bit and a 125 reading after we pulled it out of the water. I know its not getting hot. I can put my hands all over the engine.

edit
unhooked the wire and got a 304 measurement. Its been about 1.5 hr since we took it out. The engine was still a little warm. I go out later tonight or tomorrow and take a cold measurement.

 

[Silvertip]

Re: Need temp gauge help.

Better check warm resistance again. Are you using an analog or digital meter? If it's an analog meter you need to zero it with the zero adjustment know. 304 is way outside the COLD range for a 30 - 240 ohm sender. Make sure you know how to properly read the meter.

 

[ryan_289]

Re: Need temp gauge help.

its a fluke digital mulitmeter.

 

[Silvertip]

Re: Need temp gauge help.

If resistance readings are way out of whack, someone may have replaced the sender with one from a car. Wrong move!

 

[ryan_289]

Re: Need temp gauge help.

I checked last night, it appears to be the original sensor, it has gray paint on it that matches the engine. Im leaning to a bad sending unit. Is this something that is specific to the teleflex gauge? Where do I get one?

 

[Silvertip]

Re: Need temp gauge help.

Yes -- the sender must match the gauge but generally the resistance is 33 - 240 ohms for Teleflex/Faria gauges. Remove the sender. Put an ice cube on the end and measure the resistance. Then SUSPEND it in boiling water and measure the resistance. You will then get realistic readings and actually KNOW whether or not the sender is good or bad. Why buy stuff just because you are "leaning" toward the sender. You haven't proven it's bad. If it is bad, you get one right here on IBOATS. See the blue button at the very top of this page just to the right of the IBOATS logo that says BOAT PARTS AND ACCESSORIES? They provide this for free forum -- give them some of your business.

 

[ryan_289]

Re: Need temp gauge help.

Well I placed an order last night. I removed the thermostat housing to check the thermostat and found some pieces of impeller. I dont know if they were holding the thermostat open or not, but I buggered it up when I removed it. I was looking at the design of the thermostat housing and I cant figure out how the thermosat even controls water coming through the engine. All of the hoses hook up to this housing and the only hoses that are on top of the thermosat are the 2 hoses coming from the manifolds. The other hoses come in underneath the thermostat and can flow freely. Is the idea to hold water in the manifolds untill it gets up to temp and then circulate it through the engine?

Anyway it looks like my problem was the sending unit, I took it out and got odd readings, so it looks like ill have a new thermostat and sending unit. I will be out of town all next week but I will post with results when I get back. The parts should be waiting on me.

 

[ryan_289]

Re: Need temp gauge help.

Update.
Took the boat out today. The new sending unit is working but im not sure if its right. The boat runs steady at about 210. But I can put my hands on the hoses and put my fingers on the manifold by the sender. Its hot but not so hot that I cant leave my hands on it. It doesnt feel as hot as my truck does when its up to operating temp. The next time I take it out im going to bring an infared thermometer and take some temp readings.

 

[ryan_289]

Re: Need temp gauge help.

Could a dual station sending unit cause my problem? On the parts diagram there were two part numbers listed but no description. Doing some google checking today it shows that the part number I ordered is a dual station sender. I only have one gauge. Would that cause a higher reading?

Ive been looking at aftermarket sending units, are these 1/2" NPT threads?

 

[Silvertip]

Re: Need temp gauge help.

A standard sender cannot feed two gauges for the very reason (parallel circuits) I mentioned earlier. So for a dual station the sender must accommodate two individual gauges. I'm not sure about the internal makeup of those senders so hopefully Don or someone else will be by to clarify that. However, it may be as simple as having two resistance elements in one sender (same as having two separate senders). If that's the case, there would be two terminals (one for each gauge). Is this what you have and how do you have it wired?

 

[ryan_289]

Re: Need temp gauge help.

No it only has one screw terminal on it. I have it hooked up just like the old one. I just saw dual sending unit referenced to the part number I ordered when I searched it. Is there a possibility that even though my gauge pegs out when grounded it could be reading wrong? The guage goes to right between 210-220 within minutes and stays there. Doesnt matter idleing around or on long runs. I dont have an infared thermometer at home but my truck runs at 210 and I cant even touch the engine block. I can leave my hands on the boat engine. I did replace the water pump after I found the pieces in the thermostat housing but it made no change on temp readings on the gauge.

 

[NYBo]

Re: Need temp gauge help.

You may have a blockage near the sender from pieces of the old impeller, causing the block to heat up there and not elsewhere.

Do you have another gauge you could hook up temporarily?

 

[Silvertip]

Re: Need temp gauge help.

Again -- measure the resistance of the sender as you still don't know for sure what you have. If the sender says dual station then something is different about it. So here is a test of the entire system. Go to Radio Shack and buy a resistor about 100 - 110 ohms. Disconnect the sender wire from the sender and connect that wire to one end of the resistor. touch the other end of the resistor to a good grouind such as an uinpainted bolt or bracket on the motor. That resistor is replacing the sender and is providing roughly the amount of resistance to make the gauge read 1/2 scale (whatever that is). If it doesn't then the gauge is inaccurate. If it does then you definitely have an incorrect sender.

 

[ryan_289]

Re: Need temp gauge help.

There were only three pieces of impeller missing when I changed it. I found one in the pump housing and im pretty sure there were two pieces in the thermostat housing when i took it off so I think I got all of them.

Ill try to get to radio shack this week sometime and pick up a resistor to check the gauge.