Temp Gauge problems again!!
 

Ok this thing has me very confused. So far I've replaced the Tstat and the temp sender. I have checked the gauge itself also by touching the wire against a ground and it registers. The fuses are also good. I've pulled the dash and all the wires are connected. I can't figure this thing out for the life of me. Anybody know what else to check? I've done basically all I know to do.

anyone?

Hammer whats the temp gauge doing/reading, need more info

Doug

When you turn the key on it will move up to the 100 degree mark and thats as far as it gets. I was thinking first the tstat might be stuck but thats not the case, I've replaced it. Then I thought it might just be the sender but I've also replaced that as well.

Do you have thread sealant on the sender?

Did you use a Mercruiser gasket for the intake/thermostat housing?
The gasket has brass rivets in it so the sender will
be able to conduct correctly.

.......Yeah, what Scott and 35 Lightning said !

Take a volt/ ohm meter touch the
base of the sender ( sender installed)
with one lead, touch the other lead to
a known good ground, meter set on
ohm's, should read zero ohm's.
jt

Yeah the gasket is merc, it has the brass rivets in it, i didn't put any sealant on it.

jt29olhp500s - I haven't done that yet...but what I have done is taken the sender wire and touched it up against a ground and it pegged the gauge out so I know the gauge is working. Something's got to be messed up somewhere, I just don't know what else to do.

Hammer run a new ground to the gauge. I had a similar problem and that fixed it.

1 more easy check that I should
have mentioned last post,
take a jumper wire, touch 1 end to
battery neg, the other end to the
base of the sender,
this will eliminate the bad sender
ground possibilities.

jt

Gotta open this one back up. I've tried all kinda stuff but still no fix. The gauge appears to be working....when you turn the key the gauge moves, but that's it.

Could be a bad gauge. Remove the sender wire from the back of the gauge and jumper the sender lead to the ground lead. Gauge should then read either "zero" or full-hot. Anything else and the gauge is bad.

Next, run a wire direct from the sender to the gauge sender lead bypassing all the boat wiring. If it works it is bad boat wiring. If it doesn't it is a bad sender.

Take a digital OHM meter and measure across the output connector of the sender to the engine block and again to the battery negative and again to the gauge negative. They should all read the same at about 200 Ohms I think. If the are different then one has a bad ground (ie if sender to block is different than sender to battery negative you have a bad engine to battery ground).

Have someone else crank over the starter and repeat this test, if you see resitance change when cranking you also have a bad engine to battery ground.

-Greg

I did as you said and the gauge read full hot. I don't have an OHM meter but I'll borrow one and try that. I'm thinking it's just a bad ground. Maybe I should just make a jumper from the sender to the battery ground and leave it at that? IF it works of course

97BossHammer

Are your dash lights weak?
Are there other Ground issues that you may be overlooking.
I would fix the ground bus if that is the case, the temp line to the battery should be a short term fix.
Greg

Nope..dash lights are fine....no other issues that I know of. Here's something weird. When you run the boat for a while, then stop. Then after re-starting the temp gauge will shoot up to 150....then slowly go back to 100 and stay there. Man this has got me all messed up.

bump

When you shut it off the motor will heat up. When you first restart it you will see the high temp. Once the motor start pumping coolant it will go back down to running temp. It sounds like either you actually are running at about 100* (my motors will idle at 110* in the spring when the water is cold since I don't run a recirc pump or t-stat) or the resistence range for your gauge and sender are mismatched, causing it to read low.

Not all gauges/senders interchange, for example having a sender intended for a dual station (ie two gauges running off of 1 sender) will cause the temp to read low (on oil pressure gauges it causes them to read 1/2 of true). I found this when switching my Formula from full dual instrumentation to a driver/navigator panel setup.

-Greg

I had the same problem. Hopefully it is fixed, but we will see. The impeller went to shreads so I had it changed. The tech said that the gauge went bad. I took it home grounded the gauge out --- pegged, then grounded the sender wire -- pegged. I took out the sender and took a look. I noticed some red crap (loctite ??) on it that crumbled off. I took a look and put it back in. Turned the key and now at least the needle moves. Before nothing happened at all. Is this possible loctite (sealer) needed?? Should I put some on it again and reinstall or did this possibly prevent a ground the sender needed or something? I'll have the boat out today and I'll let you know what I find.
SC

Well before the boat would read at around 150 or so....now after changing the impellar it will read at 100 all the time which can't be right.

scervin - let me know what happens...maybe I'll try that with mine if yours works.

hey scervin did you ever run it again to find out?

Yeah it ran fine. Good to have a boat that isn't taking on water and runs at temp. As bad as service I got, at least it works.
SC

hmmmm....so all you did was take out the tstat and then re-install it and it works fine correct?