Mercruiser 140 exhaust manifold temp?

Jwolf87

Cadet
Joined
Jul 9, 2018
Messages
13
I was curious of what a safe temp for the exhaust manifold would be. My temp gage on dash never ever goes above 150 F but out of curiosity today on the water I put in IR gun on the exhaust manifold and it was like 450 to 500 F which seems way too hot. Does anyone know what it should be running at. The temp was taken right after 15 to 20 mins of running fairly hard.

Thank you
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,465
Ayuh,...... Welcome Aboard,...... It depends on exactly where on the manifold ya took the readin',.......

The areas near the head, have no water passages,.....
 

Jwolf87

Cadet
Joined
Jul 9, 2018
Messages
13
I'm reading it right from the top of the below and to the left of carburetor. Took temp in areas roughly in area where arrows point. Thank you.
 

Attachments

  • photo336907.jpg
    photo336907.jpg
    19 KB · Views: 2

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,465
Ayuh,...... That's hot spot,...... choke stoves used to be mounted about there,.....
 

Searay205

Chief Petty Officer
Joined
May 27, 2018
Messages
466
I don't believe it 500F, next time it reads 500F poor some water there and tell me if it boils. At least you will know if you are above or below 212. Your manifold would crack.
 

Jwolf87

Cadet
Joined
Jul 9, 2018
Messages
13
I checked it earlier that day and it said like 140F. Later that day it was anywhere between like 350F to 550F. I've never had any problem with that IR gun before. You think it was a false reading? The thing that got me thinking about heat anyways was when I ran it on muffs there wasn't much water coming out the left side of outdrive just the right side. The water that was coming out was pretty dang hot. I did replace impeller last year.
 

Jwolf87

Cadet
Joined
Jul 9, 2018
Messages
13
This was after running at idle for maybe 7 to 10 minutes on muffs. The temperature on the top of riser was at about 145F and temp onto of exhaust manifold was around 300F. Notice the amount of water coming out of outdrive on the right side in picture. (I know hard to judge from a picture) There is none coming out the left side. I did pull the hose off the top of thermostat that flows down to exhaust manifold and there was a good amount of water gushing out of that so impeller seems good.
 

Attachments

  • photo337029.jpg
    photo337029.jpg
    1.5 MB · Views: 1
  • photo337030.jpg
    photo337030.jpg
    1.9 MB · Views: 1

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,465
Ayuh,...... Where the dot is, is solid cast iron,.... there's Fire on the other side,.... Not water, that's next to it, on both sides, the head, 'n the manifold,....

Perfectly normal,.....
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
That’s way too hot for the top I’d say. You should be able to touch the top of it for about 3/4 secs normally I’d think.
 
Top