Temp issues on Mercruiser Alpha 1 Gen 2

[tank1949]

I have a 1995 Proline with twin raw water cooled 5.7 V8s. The risers and exhaust manifolds are clean with no obstructions. Yet, I have been experiencing odd temperature reading one my stb engine gauge, and before I started pulling sensors and gauges, I wanted to measure with another device. I also have a laser thermometer that I tested the heat coming through motor and manifolds. What I found was odd. The stb side of the center water manifold was about 20 degrees warmer than the left side near hoses going to risers. This is water coming directly from OD, circulating pump and not via inside of motor. I examined each temperature sender with laser and they read about 120 each but metal nipple on stb side is 20 degrees warmer. The helm gauge registers 140 degrees. I replaced stats last fall and center manifold appeared clear of any obstructions. Stb top of riser appears a bit hotter than port rise. Unfortunately, I cannot get laser inside boat to aim at top of risers, but the stb feels a bit hotter to touch. I suspect the plastic insert that aids in centering stat to metal housing is getting off centered, even though it is somewhat pressed into position and has an indent. Next test is to pull top hoses and visually compare water coming out. If water flow is about the same, any other suggestions would be appreciated. If not, I have my answere. Pull stat again!!!!!.

 

[Bt Doctur]

Step 1 in troubleshooting is impeller replacement , risers/elbows 4 years old or older are suspect.

 

[cnotecherry]

one exhaust manifold being a little hotter is normal as long as its not significantly hotter the water coming in from your o/d will also very as it passes through the coolers p/s, fuel, oil, depending on what you have I have found wonky temp readings is usually faulty t-stats are you fresh water cooled or raw? if you are raw and in salt i would change your t-stats every year maybe more I always test my t-stats before installing them a pot of water on the stove with a thermometer put the tstat in and see what temp it opens at if it is not that and all your passages are clear probably your impeller but your temp readings seam low not high so my guess would be t-stat

 

[Bt Doctur]

http://www.michel-christen.com/ExhaustElbows.pdf

 

[tank1949]

one exhaust manifold being a little hotter is normal as long as its not significantly hotter the water coming in from your o/d will also very as it passes through the coolers p/s, fuel, oil, depending on what you have I have found wonky temp readings is usually faulty t-stats are you fresh water cooled or raw? if you are raw and in salt i would change your t-stats every year maybe more I always test my t-stats before installing them a pot of water on the stove with a thermometer put the tstat in and see what temp it opens at if it is not that and all your passages are clear probably your impeller but your temp readings seam low not high so my guess would be t-stat

I don't think faulty stats. One side 20 degrees warmer than other indicates blockage. Raw water cooled. New impeller too. In fact new circulating pump as well.

 

[cnotecherry]

im not necessarily saying its a faulty stat but water is getting through when its not suppose to 140 is pretty low unless your running a 130* stat which is to low if your running it in salt water stats dont last long before getting gummed up and stick open if by center manifold you mean t-stat housing this is were you will get different temps on each side it mixes the unused cold raw water and the hot engine water and then through the exhaust one side usually gets more of the cold raw water and there is usually a side that is hotter than the other 20* wouldn't surprise me with your low temp readings I dont think you have a blockage but you might when you replaced your impellers what shape were they in if there were pieces missing they might of got caught up somewhere and that sucks to find them if you think its blockage pull your exhaust hoses off your stat housing and your elbows off you risers stick a hose in the hoses and you should be able to see if there is good flow or one flows better than the other good luck

 

[achris]

... if you are raw and in salt i would change your t-stats every year maybe more...

???? Gee, I wish I was selling parts to you...

I'm salt water cooled and I changed my thermostat last year (7 years old)... Most of the boats I work on are salt water cooled and thermostat replacement is an 'as required' item, usually around 7 to 10 years, not an annual 'service' item....

 

[cnotecherry]

I just think its like an impeller for how cheep they are and easy to replace why not do it before you have an issue with it I have only worked on a handfull of saltwater boats and eveytime the stat is or the stat housing is cloged with salt and all the other salt water stuff but I guess they were older than I thought I still think its a good idea to open the housing up and clean it every year I prefer prevention maintance not minimal and wait untill something goes wrong to fix it

 

[Moggy23]

I had similar issues with temps all over the place with my 5.7 Mercruiser, different reading on both ex manifolds & warming up was erratic with thermostat opening & closing to the point of bringing on the alarm temporary in the end. This is with a new water pump kit, eng. water pump was replaced due to a leak, new thermostat to the point of drilling a 3/16 hole in it for bypassing water.

The fix was a new thermostat housing, the old one had corrosion buildup around the water galleries restricting water flow.
The original housing 860256-C3 was replaced with a new 860258-C4 which was in my spare collection, I new it was a different part no. but I thought I would give it a go,
Runs great now, quick warm up & stays at 165 deg, both manifold are almost identical using a lazer temp gun. I got 40 knts out of it the other day in a 23 footer, still run sweet.

 

[tank1949]

I had similar issues with temps all over the place with my 5.7 Mercruiser, different reading on both ex manifolds & warming up was erratic with thermostat opening & closing to the point of bringing on the alarm temporary in the end. This is with a new water pump kit, eng. water pump was replaced due to a leak, new thermostat to the point of drilling a 3/16 hole in it for bypassing water.

The fix was a new thermostat housing, the old one had corrosion buildup around the water galleries restricting water flow.
The original housing 860256-C3 was replaced with a new 860258-C4 which was in my spare collection, I new it was a different part no. but I thought I would give it a go,
Runs great now, quick warm up & stays at 165 deg, both manifold are almost identical using a lazer temp gun. I got 40 knts out of it the other day in a 23 footer, still run sweet.

T stat housing examine is due this spring! TX!