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Volvo 57L inaccurate coolent temp readings

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"1997 Volvo 5.7L raw water coo

"1997 Volvo 5.7L raw water cooled engine on which I am getting inaccurate temperature readings indicating 140 degrees, gauge had always indicated consistent 160. Have changed thermostat and bronze sensor plug in block. Anyone have a suggested next step before changing gauge?"
 
"Make sure the impeller is goo

"Make sure the impeller is good and sending enough water to the motor. It's possible that the thermostat was in the wrong box but it's rare. There could be something jammed in the new one, too.

Is this carbed or injected? Injected has two senders- a one wire for the gauge and a two wire for the ECM."
 
"The engine is carbureted, imp

"The engine is carbureted, impeller and thermostat are new. The wire running from the brass block sensor goes into a round black unit attached to the carburetor. My next thought was to replace this wire and if that did not work to replace the gauge. What do you think? Thanks for your input."
 
"What color is the wire going

"What color is the wire going to the sender? It should be tan/black. The round part on the carb is the choke thermostat and should have a purple wire going to it.

Before replacing parts? Testing. Always test before changing parts, otherwise you'll just end up with a new boat and no money. If you plan to do more service to your boat, you'll need to become familiar with a multi-meter and electrical devices, if you aren't already.

Take the new 'stat out and look at it to see what the temperature rating is. If you have the box for the new one, look at that. too."
 
What would be the best way to

What would be the best way to test the gauge itself?
 
"You can ground the sender lea

"You can ground the sender lead and the gauge should go to its maximum. Don't put any voltage on this wire and don't keep it grounded for a long time but for a brief test, you'll be OK.

When, exactly, did the gauge start reading low? If it was immediately after changing the thermostat, it's not logical to suspect the gauge or sender. If the low reading started when you began the season, I would suspect the battery terminals (dirty or loose), the motor ground point or the terminal strip under the dash. Sitting over the winter is a great opportunity for corrosion to start/get worse and you can get all kinds of bad things going on."
 
Here I go again...

Buy a la

Here I go again...

Buy a laser pointed temperature gun (what no inboard boater should be without) and see what the actual temperature is.

JEff
 
"I first noticed the problem a

"I first noticed the problem at the end of last season. My reading went from a steady 160 to 140 max. Thinking that the thermostat was stuck open, I changed it with no result. This spring the impeller was changed and I again checked the thermostat and changed the brass sensor plug. It has only been run on the hose so far but I am still reading 140 max. I realize that this could change once in the water but I had always gotten a steady 160 whether in the yard or in the water. I will take your advice and ground the lead. I am not sure what a temperature gun might cost."
 
If your sender is mounted in t

If your sender is mounted in the thermostat housing. The gasket for the thermostat housing should have 2 brass rivets going thru it. These are to insure a good grounding circut for the temp sender.A stock aftermarket gasket does not have these.
 
"The 'riveted' gaskets

"The 'riveted' gaskets are used by Mercruiser, not by Volvo. The sender and einstruments are just a temp variable reostat and volt-meter with a different display. I do not think the engne temp has changed, more probably an elektro phenomena. Voltage drop to the reostat (sender) or from sender to instrument or ground problem in the instrument wireing. Take the instrument out of the panel and hook it up close to the sender. Take a 'clean' B+ from battery/starter and check out the reading. Is there a difference in reading when 'ignition on' eng not running and engine running? Due to the higher voltage in the circuit when engine running (charging)you should have a higher temp reading."
 
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