8.1 Horizon question

Jmac572

Active Member
Dec 20, 2016
212
Plymouth, MA
Boat Info
2004 Sea Ray 390 Sundancer "Freedom"
Engines
Twin Mercury 8.1
Hi all, looking for assistance with a MerCruiser 8.1 horizon, it’s a new to me boat… it seems to run pretty well overall but it has a hard cold start, and will not get up to temp at idle, it only gets up to about 140°… it will reach 165° while underway and holds that temp solid. Also while underway I can see a decent amount of white steam or white smoke in the exhaust of just that motor, and I get a sweet coolant smell in the engine bay. It doesn’t seem to be losing a large amount of coolant as the reservoir doesn’t seem to be emptying a noticeable amount. Any ideas? The motor is a new long block approximately 1 year ago.
 
I had 8.1s in my 360. 165 is a normal temp. 140 under no load would also be expected especially in cold water. Too many possibilities to speculate as to the source of coolant smell. As for the steam…..I always had a bit of steam coming off of the exhaust. I would submit it proves the engine is being cooled. Unless it becomes a significant amount I wouldn’t worry about it
 
I had 8.1s in my 360. 165 is a normal temp. 140 under no load would also be expected especially in cold water. Too many possibilities to speculate as to the source of coolant smell. As for the steam…..I always had a bit of steam coming off of the exhaust. I would submit it proves the engine is being cooled. Unless it becomes a significant amount I wouldn’t worry about it

Thank you… if it weren’t for the hard cold-start issue I wouldn’t even think twice about it. But the other thing is (since the boat has twins) I can compare the two, only one motor steaming under load and only one motor at 140 at idle, the other motor does get up to 165 at idle. I have a mechanic coming to look at it but we’ll see, thx for the reply.
 
Sounds like the 3 issues are unrelated to each other. Smell of AF could be a small leak on the engine and it burns off before making a puddle. Excess steam probably clogged risers and or manifolds. Hard cold starts probably fuel system. T-stat most likely stuck open causing the low temp reading.and could be the source of the coolant leak at the gasket.
 
How are your obtaining your temperature reading? (1st make sure it’s an accurate reading) If it’s from a analog gauge in the dash those are notorious for failing or not giving an accurate reading. A digital reading pushed thru your engines diagnostic connection or a heat gun would be a better source.

Here’s a quick read on Temperature gauge testing: http://www.clubsearay.com/index.php?threads/temperature-gauge-stuck.84424/
 
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How are your obtaining your temperature reading? (1st make sure it’s an accurate reading) If it’s from a analog gauge in the dash those are notorious for failing or not giving an accurate reading. A digital reading pushed thru your engines diagnostic connection or a heat gun would be a better source.

Here’s a quick read on Temperature gauge testing: http://www.clubsearay.com/index.php?threads/temperature-gauge-stuck.84424/

The previous owner updated the electronics on the boat and had a VesselView Link installed along with a 12" Simrad chartplotter. I am getting all of the engine diagnostic and operating data on the Simrad which it appears accurate. It is also showing me "Systems OK" with a green checkmark. I have researched that a bad water temp sensor could cause rough cold-starts if it is telling the computer that the engine is warm when it is actually cold, causing it to starve for fuel. But the water temp is showing accurate on the Simrad (below)... I do have a faulty water pressure sensor I believe (I have seen that the sensor will default to 43.4 psi when the sensor is not showing any voltage, I removed the connection and cleaned all the contacts to no avail so I believe the sensor is actually bad)

temp_photo_1d4a9e2336ad465813d4ee33c2d1e5c3f8817ffa.jpg
 
Check your rubber seals on the bottom of the main heat exchanger. Those rubber seals can shrink during the cold weather and seep a bit of coolant which will be evident. Your thermostat may be shot and blocked open too, but that's more involved to check since you'll need to drain some coolant and remove the heat exchanger. If you do take it off just replace those rubber seals when reinstalling.
 

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