New motor running hot

[jaybrassmonkey]

Okay so I've got my "new" reman motor in. Made the swap myself with some help from a friend and learned a LOT.
It is a mercruiser 4.3 alpha 1 gen+. Also changed the impeller. I ran the motor on the hose for a while yesterday and the temp was up. Got it out on the water today, motor is running great but temp is still upwards of 190. I know I'm getting water to the engine, had a loose hose clamp leaking, lol, got that squared away. Still hot. Pretty sure I have the 160 thermostat in, uuhm, the new motor has tapped the budget so I cannot got out and buy an infrared temp gun. Gauge "works" according to grounding the wire. New temp send installed as well. Any suggestions on what might be going on? I really DO NOT want to mess something up.

 

[wrench 3]

If it's a steady 190, not going up and down with the load on the engine, I'd be taking a second look at that thermostat.
190 is a standard automotive thermostat these days.

 

[jaybrassmonkey]

Well I ordered it in a thermostat kit from a marine parts dealer. Assuming it is a 160 t-stat. Is there a stamp or something on it?

 

[wrench 3]

The temperature is usually stamped into the "pellet" at the bottom center of the thermostat,

 

[JoLin]

Take a second look at your gauge and make sure you're reading it dead on. I bought the exact same engine last year and its normal running range on my boat is an indicated 175-180. It has a 160 deg t-stat in it. I questioned it, too.

I've been told firsthand by a couple of knowledgable marine mechs that newer engines have been running indicated (at the gauge) temps that are higher than they used to be. One guy suspects a change in the electrical system/wiring harness is responsible, like higher resistance somewhere. Proof is in your riser temps when the motor's at operating temperature. If they're warm but not uncomfortably hot you should be fine.

Not saying you shouldn't check things out and maybe test the t-stat, but there might not be an issue. The stat will have a small number stamped on it, but it should be a 160 for that engine.

My .02

 

[Watermann]

Not seeing what year your 4.3 is with no ser# but the Alpha 1 4.3 carbed versions are a 140 t-stat and my 1988 4.3 runs at 150 solid with a 140.

 

[grewvin1]

Get a spare temp gauge and test at the engine sensor direct, found some of the box stores are now selling the infrared temp gun for 20 bucks on special just got one.

 

[JoLin]

Not seeing what year your 4.3 is with no ser# but the Alpha 1 4.3 carbed versions are a 140 t-stat and my 1988 4.3 runs at 150 solid with a 140.

According to the OP it's a 'new' 4.3 Alpha Gen + (Jay, post the serial number of your engine, please). According to what I know, that's a complete factory remanufactured engine (like mine), serial number 1G400000 and up. If that's what the OP has it uses a 160 deg t-stat. Mine is 1G405446 installed a year ago.

If you look on the merc website...

https://www.mercurymarine.com/en/us/...manufacturing/

They market the 'Plus Series' complete engines and 'Pro-Series' longblocks.

My .02

 

[jaybrassmonkey]

Sorry for the confusion about the motor. I meant it is new to me, lol. It is a reman '97 mercruiser, not sure of the serial number but ends in 090M. It was just installed. I was told a new install may run warmer than normal until it breaks in a little or that the timing could be a little advanced. While running it on the river I kept checking the manifolds, only warm. The bottom of the block was HOT. Would it hurt to put a 140 thermostat in?

 

[Watermann]

Does your 97 have a carb? If so not a problem running a 140 T stat, I think the MPI with the computer and sensors out the ying yang need the heat.