1998 Mercury/Mariner 135 V6 possibly overheating? Please help I'm newb at this :(

kwik_uk

Petty Officer 2nd Class
Joined
May 25, 2011
Messages
155
Hi guys.

I finally launched Bumblebee yesterday! and by jove this is one FAST Autobot!! :eek:

It's a 1998 2.0 135 V6 Mariner with a 13.5" 23P Laser II SS prop. Pushing a 16' long x 6' beam Dateline/Sidewinder:

IMG_2336.jpg


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I've noticed that that the temperature gauge will sit dead in the middle when at idle. But once moving it will creep up to hot and say there. Is this cause for concern? High temp buzzer hasn't gone off. These are the gauges I'm using:

IMG_2323.jpg


My original temp sender was broken, not reading a single thing on the gauge. So I bought one from a chap I deal with here in the UK. I got a secondhand one as that is all that he had lying around. He said it was "just from another old V6 Merc". My question is simple: Does the sender need to match the gauge? or are there different senders that would physically fit my engine but be the incorrect version?

What I'm getting at is I think my sender is reporting falsely high temperatures.
The water coming out the tell tale is very hot, you can;t keep your fingers under it, but that's right yeah?



Now I tried to perform a basic test. I ran the engine out in the bay till it read hot. Then quickly drove 2mins back to the marina and took the cowl off so I could use my digital temp gun to read the head temps. They were around the 135F-150F on the lower cylinders and about 145F-155F on the upper cylinders. Is that correct? What should these engines run at? Idle/under load/flat out?

Just to sum up:
  • Engine water temperature gauge (brand new original Mercury Marine gauge) reading HOT after 5-10mins use.
  • Sender has just been replaced with a second hand one from an unknown engine (looks physically the same).
  • Whole water pump including all gaskets, plate and impeller + housing are new.
  • Thermostats are brand new
  • Has strong tell tale and the water from the tell tale is very hot.
  • Water defo being pumped as it's coming out of the anode area just above the anti-ventilation plate
  • With infra red temp gun Cylinder heads read 135F--145F--155F (bottom cylinders being the coolest and top being the hottest)


It has a slightly lumpy tickover at idle in forwards gear and then up to about 1200RPM but I've been told this is normal?

I'm hoping to get some video up soon.

Any help you guys can give would be great. I really don't want to damage my new engine after all the hard work that has gone into this boat!0.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,558
Re: 1998 Mercury/Mariner 135 V6 possibly overheating? Please help I'm newb at this :(

Neat on the gun readings. I use them too for all kinds of things, even cooking fish, shrimp, oysters, and french fried potatoes.....got to get the grease, I like Canola Oil, up to about 400F before you drop your treasure into the "soup" then walla, just languish in the delicate flavor. Oops, got carried away. Grin.

The merc stats are one in each bank of cylinders at the hottest spot....the top. They start to open at 143F which is stamped on the bottom of the copper pellet which is part of the stat. Your numbers are excellent......what else can I say....faulty gauge or sending unit.

Really a nice, clean boat. Ought to run as good as it looks.

Mark
 

kwik_uk

Petty Officer 2nd Class
Joined
May 25, 2011
Messages
155
Re: 1998 Mercury/Mariner 135 V6 possibly overheating? Please help I'm newb at this :(

Neat on the gun readings. I use them too for all kinds of things, even cooking fish, shrimp, oysters, and french fried potatoes.....got to get the grease, I like Canola Oil, up to about 400F before you drop your treasure into the "soup" then walla, just languish in the delicate flavor. Oops, got carried away. Grin.

The merc stats are one in each bank of cylinders at the hottest spot....the top. They start to open at 143F which is stamped on the bottom of the copper pellet which is part of the stat. Your numbers are excellent......what else can I say....faulty gauge or sending unit.

Really a nice, clean boat. Ought to run as good as it looks.

Mark

I think it was down to speed. When I'm going dead slow or at an idle then the popet valve is shut, so the heads get warmer. When I give it some throttle then more water passes through and the popet valve opens, temps go back to normal. So I can only guess that the gauge and the senders aren't faulty! :confused:

I just think it may be propped wrong at the moment. 13.5" 23p might be a bit too much. I'm going to keep a look out on ebay for a 13.75" 21p four blade Trophy Plus, or a 13.75" 21p five blade High Five. They just aren't cheap!!! :eek:
 
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