Overheating

[105mich]

Hello! I have an 89 mercury xr4 150 on a 17.5 fish n ski and it runs hot, temp gauge indicates around 200-225 degrees at idle and wide open. I just rebuilt the water pump and it works, tell tale has steady flow of water that is warm, thermostats replaced last fall as well. What else can I check? Thermostats maybe off? But I put my hand on the block and the temp feels accurate. Help!

 

[Dukedog]

over temp buzzer goin' off?.. should alarm somewhere at 190 and/or above.. not all will alarm at same temp.. usually closer ta 210 and above… water pressure gauge?

boat/motor new to you or has this jus started?

 

[Texasmark]

Hello! I have an 89 mercury xr4 150 on a 17.5 fish n ski and it runs hot, temp gauge indicates around 200-225 degrees at idle and wide open. I just rebuilt the water pump and it works, tell tale has steady flow of water that is warm, thermostats replaced last fall as well. What else can I check? Thermostats maybe off? But I put my hand on the block and the temp feels accurate. Help!

"I put my hand on the block and the temp feels accurate." Bingo!

A US Domestic hot water heater in the Normal position controls water at 140F. 143F (the opening temp) is stamped on the thermostat pellets for that engine and should be what is installed. You figure out how long you can hold your hand under a faucet that has equalized in temp with the HOT water only running! The opening range of temps would be another 10-15 degrees but at idle the stat would just open and close staying around 143 (tolerances 5% maybe due to manufacturing variances).

Water boils at 212F at sea level. Steam starts occurring at around 200.

Your hand is your most accurate "gauge" in this case.

 

[105mich]

Buzzer does not go off, I never let the temp go far above 200 before I shut it down, I know the thermostats are 143s and should be able to put hand on the block for a few seconds without burning but not keep it on forever. Is there a way I can flush out the block with a hose to see if there is any obstruction? Or would the poppet valve have any effect?

 

[Chris1956]

The poppit valve controls the cooling above about 2000 RPM. It is time to inspect/rebuild it.

 

[Dukedog]

Buzzer does not go off, I never let the temp go far above 200 before I shut it down, I know the thermostats are 143s and should be able to put hand on the block for a few seconds without burning but not keep it on forever. Is there a way I can flush out the block with a hose to see if there is any obstruction? Or would the poppet valve have any effect?

if your not gettin' a "buzzer" your gauge is off as most "metal" reading gauges are..it needs ta be checked with a temp gun and verified for what its reading.. tha buzzer doesn't lie 99% of tha time... 150* is "hot to tha touch...200, 1/2 a second touch is to long... unless your a brick layer!

 

[105mich]

I have been able to confirm the gauge is way off. I ran a TC underneath the temp sender and when the gauge said 250 degrees the TC only read 140. I ran the boat all day and never got a beep, the gauge was saying above 200 degrees and the TC was consistently at 140 all day

 

[Faztbullet]

That the reason they make water pressure gauges as temp gauges are inaccurate as you found out.

 

[Texasmark]

Moving right along with this since I decided to go with a temp gauge......why should I rely on a pressure gauge? I'm idling around in the No Wake zone before blasting off in open water......stat is stuck shut for an example.....which happened on the previous used boat I bought.....by the time I hit open water the horn was sounding.....didn't have any type of accessory gauge. More to the story but that gets us to the point.

So, having a new, tested temp gauge, and knowing where 143 is on the dial (position of the indicator, not necessarily the number to which it refers), and I see the temp inching up toward 200 (which is a good ways across a gauge dial of 100 to 250) I can easily see that something is wrong.

With a pressure gauge, on a cold day, cranking up and idling out as I mentioned, how will a pressure gauge help me there? Since the engines have poppets for operation above 2500 rpms (service manual number) and once clear of the buoys, you hammer down on it to get where you are going, how do you know you had a bad stat with just a pressure gauge?

 

[Faztbullet]

First you make sure horn and sender work as it will alarm @190. Pressure gauge you can see the t-stat and poppet open with the pressure drops. Also if pressure to high can tell if poppet or t-stat stuck. Factory OEM gauges do not have numbers but a area needle falls in....If it has numbers its either a aftermarket or 4 stroke gauge

 

[Dukedog]

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