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View Full Version : Temp gauge reading increases when accessories powered up


Luv2Ski
10-05-2010, 03:46 PM
Hey folks,

My prostar typically runs around 170 deg, gauge in general appears to work as it should.

However, with each accessory I power up the engine temp reading will increase by about 5 degrees. So, if I switch on the bilge, it will it 175, lights 180, heater and I am pushing 190.... etc. This works both ways (switch them all off and temp instantly back to normal).

Clearly this just has to do with the increased electrical draw and not actually a change in engine temperature. Not really a concern per say, but it is a bit unsettling when the high temp alarm goes off (I am compelled to turn off the accessories even though I know it is a false reading).

Is this normal? If not, any suggestions?

THANKS!

88 Prostar 190, 351w

thatsmrmastercraft
10-05-2010, 03:54 PM
My guess would be a bad ground for the temp gauge.

ahhudgins
10-06-2010, 08:18 AM
Before I can give any suggestions, I have a few questions:

#1 Does your temperature gauge work correctly at all other times? It starts at the
maximum cold position when it's first started and then moves to the 170 degree point?

#2 What do the other gauges do when this happens?

#3 To verify your gauge wiring, remove the tan wire from the temperature sending unit and
see if the temperature gauge drops to the cold position.

Luv2Ski
10-06-2010, 10:48 AM
My guess would be a bad ground for the temp gauge.

Connection to the sending unit is clean. I should remove the unit and clean both sides of the threads and see if that helps. I tightened all the gauge connections when I had the dash out a few months ago, so pretty sure it is all good on that end.

cbryan70
10-06-2010, 11:06 AM
my old boat does this as well. When i turn the blower on i lose a quarter tank of gas. Always fun when at idle i forget I have the blower on and think ive gone through alot more gas then i should then realize its on and turn it off

Luv2Ski
10-06-2010, 11:19 AM
#1 Does your temperature gauge work correctly at all other times? It starts at the maximum cold position when it's first started and then moves to the 170 degree point?

Yes, works exactly as one would expect at all other times. I suppose I don't know for certain that the readout is correct when it runs at 170, but that seams in the ballpark to me with a 160 deg thermostat

#2 What do the other gauges do when this happens?
When an accessory if first switched on I may see a brief very bounce in the voltmeter, maybe the oil pressure gauge as well, but I believe they will quickly read normal after that. I will verify next time I am in the water.

#3 To verify your gauge wiring, remove the tan wire from the temperature sending unit and see if the temperature gauge drops to the cold position.

I will do that next time I get to the water, which should be this weekend. Given that the gauge reads more or less correctly I suspect the wiring is correct but certainly worth investigating.

Thanks

Luv2Ski
10-06-2010, 11:23 AM
my old boat does this as well. When i turn the blower on i lose a quarter tank of gas. Always fun when at idle i forget I have the blower on and think ive gone through a lot more gas then i should then realize its on and turn it off

Interesting that you have the same symptom on a different gauge. Do any of your other gauges change?

190 Skier
10-06-2010, 01:55 PM
My 1990 PS 190 does the same thing. Worse is when I plugged a spot light into the Aux port and it immediately jumped to 220 degrees with the alarm going off. That is very unnerving when it is dark and you are trying to navigate a strange lake looking for a houseboat. I thought I was toast until I finally figured out what was going on. It all turned out good and just got back from 4 days of glass on Lake Shasta, did not see one other skier or boarder the whole time! Anxious to know if anyone knows how to correct this.

ahhudgins
10-06-2010, 03:12 PM
It is very common to see all of the gauges drop (go to the left) when more accessories are turned on, especially in older boats. The gauges have one side connected to 12V and the other side connects to a sensor that acts like a variable resistor to ground. It only takes a small resistance change to see a change on the meter. If you have any bad connections in the meter circuit, you will have less current flow and the meter will have less deflection (moves to the LEFT). Also, if you turn on a blower or a large flood light, your battery voltage can drop 1 or 2 volts and this also causes less current to flow through all of the meters.

I used to own an 87 Prostar and I fixed this problem by rewiring my dash. The wiring behind my dash had a bunch of those crimp connectors between the gauges. I installed two terminal strips under my dash; I connected one strip to the 12V from the ignition switch and the other directly to the battery ground. I then removed all of the crappy wiring between the gauges and ran a 12V wire and a ground wire to each gauge. Problem solved. I can hand draw a picture of what I did and post it since I donít have the boat any more.
I have a theory as to why one gauge deflects MORE, but I would have to get some one to test it with a voltmeter. I think rewiring the dash would fix that problem as well.

03geetee
10-06-2010, 03:27 PM
My boat does this too, not to bad though just a little movement when I activate the blower or bilge.

JTR

87PS190
10-06-2010, 08:55 PM
I used to own an 87 Prostar and I fixed this problem by rewiring my dash. The wiring behind my dash had a bunch of those crimp connectors between the gauges. I installed two terminal strips under my dash; I connected one strip to the 12V from the ignition switch and the other directly to the battery ground. I then removed all of the crappy wiring between the gauges and ran a 12V wire and a ground wire to each gauge. Problem solved. I can hand draw a picture of what I did and post it since I donít have the boat any more.
I have a theory as to why one gauge deflects MORE, but I would have to get some one to test it with a voltmeter. I think rewiring the dash would fix that problem as well.

I'll play....mine does this this too. Turn on the blower and lose a quarter tank of gas and temp gains 15-20 degrees....been wanting to do something about for a long time now.:rant:

deereman
10-06-2010, 10:40 PM
same exact thing on my 87 too...

ahhudgins
10-06-2010, 11:24 PM
My buddy has an 87 or 88 Prostar and I will pull his dash this weekend if his wife allows him to come to the lake this weekend.8p All of his gauges drop when he turns on his blower and he has been wanting me to look at it for him. As you guys can see, it's a common problem on the older boats. I'll look at his and see what could cause the temp gauge to go UP when the others go down. This wiring diagram shows how most gauges are connected. The gauges on my 87 had a bunch of wires crimped together that went to a lot of other places (I drew in the bottom corner). I took all of the old wires out and connected them to one common point (a new terminal strip) just like diagram shows. I ran a larger wire from the ignition switch and connected it to a new terminal strip. I put crimp terminals on the wire ends and also soldered the terminals and then covered them with heat shrink. As I have found on my 95 Maristar, the boat wiring doesn't always match the manual.

ahhudgins
10-11-2010, 01:25 PM
Checked a 87 Prostar this weekend and all of the guages drop when the blower is turned on. This is due to "voltage drop" from the battery to the hot wire on the gauges. Use a digital volt meter and put the negative lead on the negative battery terminal. Start the boat and check your battery voltage at the battery. Turn the blower on and the voltage should stay the same. If it doesn't, then you have a charging issue. Turn the blower off.

Leave your negative lead on the battery and put the positive lead on the red wire of one of the gauges. It could be a purple wire depending on the year boat. Each gauge has a ground wire (black), blue wire (lights), and the 12V wire (red or purple). Should be 12-14V.
It could be a little less than 12V depending on the number of connections and splices between the battery and the terminal. Turn the blower on again. If the voltage drops a volt or two (or more) you have a connection problem between the battery and the gauges. My 87 had a bunch of cheap splices behind the dash that caused my problem.

If your battery voltage stays up but gauges go down, you are losing a few volts in the wiring. If one gauge is going up and the others are going down, then you have a good connection on the one gauge and a bad connection on the others. That is just my guess because I havn't seen one that, but I'm sure I could find the problem with just a volt meter.

Luv2Ski
10-11-2010, 01:41 PM
Seams pretty common, I am surprised there has not been threads on this in the past (that or my search terms did not find them).

I played with it this weekend. Indeed, multiple gauges move, direction depends on the gauge. Voltmeter and fuel decrease, oil pressure and engine temp increase. Tach (and of course speedos) are not affected.

In my case, I know I have only ~0.2 volt drop between the battery and my ignition switch as I was testing that recently while troubleshooting an unrelated problem. As such, it sounds like I should look into rewiring the gauges to a good source of power as suggested.

I will probably put this off for a bit as I have a few freak days of 80+ degree weather and want to keep the boat ready to hit the water. Not to mention the stack of wood I should be spiting...

ahhudgins
10-11-2010, 05:33 PM
Seams pretty common, I am surprised there has not been threads on this in the past (that or my search terms did not find them).

I played with it this weekend. Indeed, multiple gauges move, direction depends on the gauge. Voltmeter and fuel decrease, oil pressure and engine temp increase. Tach (and of course speedos) are not affected.

In my case, I know I have only ~0.2 volt drop between the battery and my ignition switch as I was testing that recently while troubleshooting an unrelated problem. As such, it sounds like I should look into rewiring the gauges to a good source of power as suggested.

I will probably put this off for a bit as I have a few freak days of 80+ degree weather and want to keep the boat ready to hit the water. Not to mention the stack of wood I should be spiting...

All of the gauges dropped on my 79 S&S and my 87 Prostar when the blower was turned on. I don't have this problem on my 95 Maristar 200. A lot of people just live with or don't want to go through the hassle of rewiring. I'm an electronics technician and I don't just jump in and rewire every thing until I've checked it with a meter. I had about a 3V drop on the hot wire for my gauges so I just started at the gauges and worked my way back. I used slightly larger wire, put new crimp terminals on the wire ends (and soldered), then covered with heat shrink tubing. I know every one is looking for a quick fix, but takes a little bit of work. It was worth it to me to be able to turn on the blower and my gauges didn't move.:) I'll be glad to help any one out who needs more advice on this subject.

87PS190
10-11-2010, 05:34 PM
Thanks for looking into that ahhudgins. I'm going to look into the rewiring, and add another battery. Getting tired of the stereo going off while starting up too.

ahhudgins
10-11-2010, 05:49 PM
If you save and print out the wiring diagram that I posted, it shows the "ideal" wiring: All of the gauges have their own hot wire running to the IGN terminal on the ignition switch. My 87 had one wire running from the IGN terminal and then each gauge had a splice on it, the kind that you get at a auto parts start....lay each wire in the splice side by side then crimp it with a pair of pliers. I old and dirty ignition switch can cause problems too.

BTW, my 87 was the exact color scheme as yours right down to the trim. Mine was the power slot and I put an OJ 4 blade on it and a tower (black). I loved the boat but traded it in on the Maristar because the kids were bringing more friends to the lake every weekend. My kids have gotten older and rarely come to the lake any more and I'm kicking myself every day for trading in my Prostar. Oh well, the things we do for our kids.:rolleyes:

87PS190
10-11-2010, 06:42 PM
If you save and print out the wiring diagram that I posted, it shows the "ideal" wiring: All of the gauges have their own hot wire running to the IGN terminal on the ignition switch. My 87 had one wire running from the IGN terminal and then each gauge had a splice on it, the kind that you get at a auto parts start....lay each wire in the splice side by side then crimp it with a pair of pliers. I old and dirty ignition switch can cause problems too.

BTW, my 87 was the exact color scheme as yours right down to the trim. Mine was the power slot and I put an OJ 4 blade on it and a tower (black). I loved the boat but traded it in on the Maristar because the kids were bringing more friends to the lake every weekend. My kids have gotten older and rarely come to the lake any more and I'm kicking myself every day for trading in my Prostar. Oh well, the things we do for our kids.:rolleyes:

That's funny, I'm going through the same problem! We waited quite a while before having our kids (guess it was all the boating trips and vacations!!) but now I'm thinking we need more room too. Not sure how it's going to play out yet...:confused:
Thanks again.

Luv2Ski
10-12-2010, 10:38 AM
My kids have gotten older and rarely come to the lake any more and I'm kicking myself every day for trading in my Prostar.

but now I'm thinking we need more room too. Not sure how it's going to play out yet...:confused:


Sounds like a trade is in order :cool:

cbryan70
10-12-2010, 01:15 PM
Interesting that you have the same symptom on a different gauge. Do any of your other gauges change?

Bat goes down, gas goes down, oil i beleive goes down or up cant remeber

Starshack
10-12-2010, 02:53 PM
I had this problem on my 89 PS. I don't like the daisy chain wiring method. Best thing to do is install 2 terminal blocks and run your hot & ground directly from the respective blocks. My 92 PS does not do it for some reason.

87PS190
10-12-2010, 08:28 PM
Sounds like a trade is in order :cool:

Ahh yes but I'm leaning toward keeping the 87 so I don't feel the remorse he has!!