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Max Online: 36273 @ 01/23/13 02:34 PM
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#11387808 - 02/02/16 08:21 PM '96 Merc 150 EFI running hot only at idle
TexasPescado Offline
Pro Angler

Registered: 10/06/05
Posts: 764
Loc: Rowlett
Got an overheat alarm last weekend after about a 20 min idle. The motor was peeing good and not running poorly at all. I put it up on pad and it cooled down instantly. Any ideas what this could be? I had also just replaced the thermostats with brand new 143 degree thermostats as preventative maintenance prior to this trip. I noticed it was running a little hot on a trip prior to this but never got an alarm so I don't think it's the thermostats.

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#11387873 - 02/02/16 08:49 PM Re: '96 Merc 150 EFI running hot only at idle [Re: TexasPescado]
Ol Man River Offline
Extreme Angler

Registered: 06/16/11
Posts: 1410
Loc: SE Texas
How old is the impeller?

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#11387919 - 02/02/16 09:08 PM Re: '96 Merc 150 EFI running hot only at idle [Re: Ol Man River]
TexasPescado Offline
Pro Angler

Registered: 10/06/05
Posts: 764
Loc: Rowlett
Originally Posted By: Ol Man River
How old is the impeller?


The impeller & housing was replaced last year around this time.

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#11387924 - 02/02/16 09:11 PM Re: '96 Merc 150 EFI running hot only at idle [Re: TexasPescado]
Ol Man River Offline
Extreme Angler

Registered: 06/16/11
Posts: 1410
Loc: SE Texas
Constant alarm or intermittent? Poppet valve?

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#11387952 - 02/02/16 09:23 PM Re: '96 Merc 150 EFI running hot only at idle [Re: TexasPescado]
TexasPescado Offline
Pro Angler

Registered: 10/06/05
Posts: 764
Loc: Rowlett
It was constant until I put it up on pad and it cooled it off. It looked to be peeing real strong the whole time though...even at idle where it was running hot. Most of the issues I've been reading about with the poppet valve seem to be overheating at WOT and cooling at idle...I'm having the exact opposite problem.

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#11388024 - 02/02/16 10:09 PM Re: '96 Merc 150 EFI running hot only at idle [Re: TexasPescado]
TLW Online   content
Extreme Angler

Registered: 11/16/06
Posts: 2236
Loc: ft worth
water pressure gauge?

pump.... replace with an oem "complete water pump kit".... first thing ya do with an unknown heat problem of any kind.

ya might check tha stats for clean then in a pan of water on tha stove makin' sure they open and CLOSE....


Edited by TLW (02/02/16 10:40 PM)

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#11388111 - 02/03/16 12:18 AM Re: '96 Merc 150 EFI running hot only at idle [Re: TexasPescado]
LOSTTEXAN Offline
Outdoorsman

Registered: 05/10/09
Posts: 47
Loc: Pensacola, Fl
Poppet valve can cause overheat at idle, and cured at higher rpm if it is stuck partially open by debris. Higher rpm compensates and overcomes low rpm water volume
Have personally experienced it.

After checking poppet first,(it's easier), I would check water pump next.

The housing and especially the base plate has to be perfect, no deformed plastic and no grooves or galling at all.
_________________________
Grew up on Tawakoni and Texoma before hybrids and stripers existed on either.

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#11388133 - 02/03/16 03:33 AM Re: '96 Merc 150 EFI running hot only at idle [Re: TexasPescado]
TLW Online   content
Extreme Angler

Registered: 11/16/06
Posts: 2236
Loc: ft worth
pensacola? been there long? we jus moved back ta tx. after spendin' first 3 years of retirement on tha island there.. been home almost a year but we both miss tha beach, food/bars n music!

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#11388169 - 02/03/16 05:54 AM Re: '96 Merc 150 EFI running hot only at idle [Re: TexasPescado]
PlanoPaul Offline
Outdoorsman

Registered: 12/16/13
Posts: 215
Loc: Plano, TX
Poppet for sure. Had a 225 VMAX do the same exact same thing.

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#11388222 - 02/03/16 06:43 AM Re: '96 Merc 150 EFI running hot only at idle [Re: TexasPescado]
gary purdy Offline
TFF Guru

Registered: 05/24/03
Posts: 11205
Loc: Littlefield Tx & Lake A. H. US...
Agree with the poppet assembly. Many times I only have to replace the rubber seal in the block.#16 here: http://www.boats.net/parts/search/Merc2/Mercury/V-150%20EFI%20%282.5L%29/0T409000%20THRU%200T800999/EXHAUST%20MANIFOLD%20AND%20EXHAUST%20PLATE/parts.html
_________________________
The world will not be destroyed by those who do evil, but by those who watch them without doing anything. Remember what He has done and remember that He is not done yet!-- GOD IS GOOD

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#11389123 - 02/03/16 01:00 PM Re: '96 Merc 150 EFI running hot only at idle [Re: TexasPescado]
TexasPescado Offline
Pro Angler

Registered: 10/06/05
Posts: 764
Loc: Rowlett
Thanks guys. I'll go and replace the poppet assembly and see if that cures it. Seems pretty easy and inexpensive for a DIY job and I found a great YouTube step by step video for the replacement.

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#11390708 - 02/03/16 11:49 PM Re: '96 Merc 150 EFI running hot only at idle [Re: TLW]
LOSTTEXAN Offline
Outdoorsman

Registered: 05/10/09
Posts: 47
Loc: Pensacola, Fl
Originally Posted By: TLW
pensacola? been there long? we jus moved back ta tx. after spendin' first 3 years of retirement on tha island there.. been home almost a year but we both miss tha beach, food/bars n music!


Been in Pensacola since 2004, pounding the offshore scene.and bands on the beach
_________________________
Grew up on Tawakoni and Texoma before hybrids and stripers existed on either.

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#11390772 - 02/04/16 02:49 AM Re: '96 Merc 150 EFI running hot only at idle [Re: TexasPescado]
TLW Online   content
Extreme Angler

Registered: 11/16/06
Posts: 2236
Loc: ft worth
yeah tha island was a very good, slow and easy time 'cept for tha one freaky ice storm we got.

.............later.

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