3.0 litre Mercruiser Temp Issue

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Denis O

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My boat (Chaparral 180SSi) is spending it's first summer in the water after being Coppercoated back in April Of course, the leg is now getting a liberal coating of all things green.

Took her out last week and the engine was running slightly hotter than normal. Gauge starts at 120F and normally runs at 140F. It was actually running at 150F but would drop to 140F when on tickover. I wasn't too concerned and just asked the guy who looks after the mooring to get 1 of his lads to clean the leg.

Roll onto yesterday and once started it warmed up to 140F then, within a few hundered metres, dropped back to 120F. Checked all the obvious bits around the engine and could see nothing obvious. Once we got underway again the temp then got up to 180F which is about midway up the gauge. Stopped to check all OK and again nothing obvious. Took off again and gauge dropped to 120F and stayed there for the rest of the day. At no point did we get steam/smoke or rough running.

I'm guessing either thermostat, (do they have 1) although unlikely.

Temp sensor probable

Temp gauge possible.

Here's hoping it's something simple and cheap to fix.
 
Generally, depending on the thermostat installed, the temperature should sit between 175 and 195 degrees Fahrenheit which is between 80 and 90 degrees Celcius.

140 degrees is too low and would suggest that the thermostat is sticking open and cooling the engine too much. I would replace the thermostat, if the engine runs too cool it will wear the engine as the oil isn't up to operating temperature.


Mark
boatdoctorni.com
 
Hi
If it was blocked waterways or impeller problem then it would be there all the time. As already mentioned I would be looking at the thermostat, remove it, de-crud and clean, pop in hot water and check opening/closing temps, that's if it is working!. Usually it will be a replacement item. Just to make sure you could do a run with out it fitted to see if the problem has gone away (no cost!) If it is still there then it's not the stat.
Let us know how you get on.
 
Peanuts said:
Hi
If it was blocked waterways or impeller problem then it would be there all the time. As already mentioned I would be looking at the thermostat, remove it, de-crud and clean, pop in hot water and check opening/closing temps, that's if it is working!. Usually it will be a replacement item. Just to make sure you could do a run with out it fitted to see if the problem has gone away (no cost!) If it is still there then it's not the stat.
Let us know how you get on.
Click to expand...
There is a problem with this approach, some raw water thermostats redirect the cooling water direct to the exhaust when closed. If the stat is missing the water can go anywhere i.e. line of least resistance, the engine may still overheat. I'm not sure this applies to the 3.0ltr. Mercruiser
 
Thanks for the suggstions folks.

For info the engine is raw water cooled and in the 3 years I've had her she's always run at about 140F. She's a 2003 boat but was never used by the guy who imported her so only had 1.5 hours on the clock when I bought her. She was fully service with new impellor before we used her. When we first put her in the water I had some running problems which turned out to be crud in the tank that had built up over 7 years of non use, that the fuel then turned into sludge that blocked the fuel tank pick up. Slow running fine but when you opened the throttle the engine died. Cleaned out tank and perfect.

It was last serviced with engine and gear oil, impellor etc just over a year ago but it's only done about 12 hours since then so the engine oil is still peachy clean.

Perhaps the stat could have developed a non use related problem and the fact that it's never run at the correct temp may well point to that.

Easy enough to change the stat I guess, whilst she's still in the water, so I'll give that a try and see what happens.

Last year I had the fuel gauge throw a wobbly and refuse to drop below "FULL". I've put that down to the sender and must get that sorted when she comes out of the water in October. It appears that non usage can come with it's own set of problems.

I'll report back once the stat has been changed.
 
a thermostat is designed to open up at a set temp and this can be tested in a saucespon on the missus best and a temp gun from fleabay for a tenner.(always handy to have.)
http://www.ebay.co.uk/itm/NEW-Non-C..._Measurement_Equipment_ET&hash=item232c5945fd
there's a wax that melts at the stated temp on the thermostat that can be tested but if the flap in the exhaust horn may have melted and fell to the bottom of the down pipe and this can restrict flow too.as its designed to stop water being sucked into the engine when decelerating as the stern wave hits the transom when coming off the plane.these can often be found stuck in the lower transom gimbal outlet but are a pain to remove.only a few suggestions, as well as a hose from the gimbal to the upper side of the uj bellows being fitted wrongly.i would always start with an impellor though to eliminate this as a mechanic may say its been done but unless i have proof of the replacement i would be starting there first.not a hard task to diy especially if you have a 2nd pair of hands
A choked manifold riser can also give bad temp figure especially if running in brine and its not flushed with fresh water on the same day.
i also assume the greenery has been removed from the leg at the water inlets as in your opening statement.
 
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I just had temp problems and for the sake of about £30 you might as well change the thermostat and impellor. Sounds like a thermostat prob. No doubt you will find other bits while your in there as i did so worth doing.
 
We have a boat with the same engine, at three years old the thermostat failed at sea so I removed it to get us back to port and for a few subsequent trips until a new one was procured with out any apparent problems.
Now, three years on, if the boat has been stood more than a few weeks on start up the thermostat seems to stick a little, first heating to 3/4 across the gauge, then cooling rapidly to 1/3 (presumab,y when it opens) then settling at just under 1/2 which is normal, then works fine.
I just make sure I keep an eye on the gauge on initial staring till it settles incase one day it stays stuck.
 
markdj said:
Generally, depending on the thermostat installed, the temperature should sit between 175 and 195 degrees Fahrenheit which is between 80 and 90 degrees Celcius.

140 degrees is too low and would suggest that the thermostat is sticking open and cooling the engine too much. I would replace the thermostat, if the engine runs too cool it will wear the engine as the oil isn't up to operating temperature.


Mark
boatdoctorni.com
Click to expand...

I've had these engines in two of my previous boats and can confirm the thermostats are 140 degree jobs
 
Denis O said:
Thanks for the suggstions folks.

For info the engine is raw water cooled and in the 3 years I've had her she's always run at about 140F. She's a 2003 boat but was never used by the guy who imported her so only had 1.5 hours on the clock when I bought her. She was fully service with new impellor before we used her. When we first put her in the water I had some running problems which turned out to be crud in the tank that had built up over 7 years of non use, that the fuel then turned into sludge that blocked the fuel tank pick up. Slow running fine but when you opened the throttle the engine died. Cleaned out tank and perfect.

It was last serviced with engine and gear oil, impellor etc just over a year ago but it's only done about 12 hours since then so the engine oil is still peachy clean.

Perhaps the stat could have developed a non use related problem and the fact that it's never run at the correct temp may well point to that.

Easy enough to change the stat I guess, whilst she's still in the water, so I'll give that a try and see what happens.

Last year I had the fuel gauge throw a wobbly and refuse to drop below "FULL". I've put that down to the sender and must get that sorted when she comes out of the water in October. It appears that non usage can come with it's own set of problems.

I'll report back once the stat has been changed.
Click to expand...

do you know when the exhaust riser and manifold were last checked or changed, whilst unlikely given the symptoms, it could be the water jacket surrounding the riser is becoming blocked and something had difficulty passing through blocking the water circulation for a while. I'd be going after the thermostat too as a first measure
 
OK. New thermostat now fitted and apart from a minor water leak from the top of the housing all seems well. Sea's a bit rough off Gouvia today so only went for a quick spin a couple hundred metres off the pontoon. Temp gauge went straight up to 14oF on tickover. Once I opened her up it was up to 180F and then dropped back to 140F. It looks like the new stat is working. Seems happy ticking over at 140F which is what it always use to do.

The stat that came out was proper clogged with rust and crud and you could see where it was stuck open. Onlu about 1/2mm all round but enough to let water through continuously.

I bought the new stat €28, top gasket €3, bottom gasket €6 which seems hellishly expensive to me. I then had to butcher the plastic sleeve out so had to ge back to the dealer for a new sleeve €10. So €47 for a thermostat change WTF.

For those that asked, the old stat was 160F as was the new 1.

The risers and manifolds have never been changed but the boat has only done 3 seasons and 61 hours in the water and this year is the first time it's been left in the water. Always flushed with clean water when it used to be trailered although not flushed so far this year. It went into the water on 21st May and I didn't realise it needed to be flushed. Next job tomorrow morning will be to add some gasket sealant to the stat housing (is that acceptable) and then get a couple of hours on the water and then flush with fresh back at the pontoon.

Thanks to everyone who has contributed.
 
One final up-date. Today I introduced some gasket sealant, put the housing back together and low and behold, dry as a very dry thing :D

Truth be told, whilst I moved the boat from it's mooring buoy to the pontoon, with engine running for about 5 mins, there was no leak anyway. I still decided to use the gasket sealant as a belt and braces job as it only took about 5 minutes anyway.

Managed a couple of other jobs; replaced a couple of pop studs on the bimmini, tightn'd the bow fender rope, cleaned her up a little and round to the marina for a fill up (€123.47) :eek: and it's only a 21 gallon tank. All ready for a zip up to Agni tomorrow....winds permitting.

Thanks for all the help on here as well. Cyber beers for all.
 
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