1988 mercruiser 5.0lx/alpha1 gen 1 expert needed

[Bondo]

my thermo housing has 2 sensors i did replace starboard side sensor

Ayuh,.... 1 is the temp sensor, the other is the alarm switch,....

,but something wrong with temp gauge ,should i just get new gauge

That's what I see,....

 

[biggjimm]

With the ignition on, ground the terminal on the temp sender & the gauge should peg out to the hot side. If not the gauge is bad. If the gauge works & it still registers hotter than what the engine is actually running (confirmed with your infrared temp gun) then the temp sender is faulty.
But as Bondo said, one of those sensors is for your alarm so make sure you check the correct one when testing the gauge.

Good luck.
Jim.

 

[newtoboat101]

thanx bigg jimm

 

[newtoboat101]

well ...when i grounded it pegs ,and thats a new sender ,maybe wrong sender for this application,,ill put old sender back on and see what happens, this is new sender is sierra part 18-5897 thats what i have on now

 

[biggjimm]

Make sure you've got continuity from the body of the sending unit to ground. I've seen guys get so crazy with thread sealer compound or Teflon tape that the sending unit isn't making metal to metal contact with the intake or stat housing causing an open in the circuit. The sender has to be grounded to whatever it's threaded in to to work.
Also, some have the rivets in the t-stat gasket for the same reason. Not sure if that's applicable to your setup or not.


Jim.

 

[newtoboat101]

yes i have rivets in gasket ,also when i grounded it, i ran wire from sender to thermostat housing bolts ,the bolts that go into motor ,it pinned needle ,so i'm thinking both thermo housing bolts must be grounding ,which is good?,and my sender works ,because it pinned with ground. i did not use any thread sealer or form a gasket i will know a little more tonight gonna switch to old sender see how gauge reacts

 

[newtoboat101]

come to think of it ,i used a little teflon tape on sender will also go without to see if works thanx

 

[biggjimm]

Yes, ground at the stat housing & bolts is a good thing.
You could still have a situation where the sender is not grounded to the housing though.
To keep from going on a wild goose chase check it with your dvm or when you ground the terminal to check the gauge, ground it to the sender body & if the gauge still pegs you know the sender is in fact grounded.

If you only used a couple wraps of Teflon that should not be the issue but you never know til you check sometimes.
Jim

 

[Bondo]

If you only used a couple wraps of Teflon that should not be the issue but you never know til you check sometimes.

Ayuh,..... 2 things come to mind,.....

If the t-stat housin' was installed with gaskets that Don't have the little brass rivet in 'em,..... Ya ain't gonna have a solid ground,....

When installin' senders, 'n switches,.... Ya use plumber's Paste thread seal, not teflon tape,....

 

[newtoboat101]

changed back to old sender ,ran motor got the same result ran up to 190 in about 8 minutes ,BUT this time when I ran my infrared gun everything thing was in the 125-160 range ,except right over the spark plug area where the cylinder head meets the motor only in a 1/4 inch area behind exhaust it went to 195,right where the most heat would from piston firing,outside that area 160 what kind of range should I see in that area? ,and that 195 temp near cyl. head would that mean that my temp gauge is accurate ?what area should I concern my self with to figure okay temp?(thermo housing /hoses)

 

[newtoboat101]

water coming out was 125 degrees

 

[Bondo]

what kind of range should I see in that area? ,and that 195 temp near cyl. head would that mean that my temp gauge is accurate ?what area should I concern my self with to figure okay temp?(thermo housing /hoses)

Ayuh,.... Yer ray-gun works Right, but not the gauge,...

The gauge reads the water temp at the t-stat housin',.....

The Hot area is the exhaust ports comin' outa the heads, into the manifolds, which is a dry area, no water exactly right there, hence the heat,....
Water is in the heads, 'n in the manifolds, just not where they meet,...