Can I run my engine without a thermostat? (Mercruiser)

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Mongoose

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Hi. I have a boat with a 5 litre petrol V8 Mercruiser with a Alpha drive.(2001)
I run wholly in salt water.The boat is moored in salt water, and so does not see any fresh water from April to end of September!
I have had 2 thermostats stick closed on me in the last three years, and was wondering, is it ok to run the engine all season without a thermostat in place.
I am aware it will take longer to warm up, and the fuel consumption while getting warm will be worse.
Im sure I have read on some American web sight that it could cause engine damage, but I can' t find it again, and what, if any engine damage could it cause?
 
I've run petrol engines without thermostats. You've identified the problem of a slower warming up period. As long as the engine eventually gets up to temp and you take it easy until it does (otherwise the thicker oil might mean inadequate lubrication) I can't see any other problem.
 
There could be an issue with poor tickover if it doesn't reach or maintain a good temperature.
The problem with cooling that may occur, especially on V engines is that without the restriction caused by the thermostat water will flow through on the path of least resistance and scavenging of hot water from more remote parts of the heads may occur, leading to hot spots.
On race and rally engines run without thermostats (talking old money here) the fix was to remove the actuating part of the thermostat but re-install the plate and any baffles in the head. This kept the flow down to near the designed rate and allow scavenging from the far ends of the heads.
Worth trying.
 
the engine runs coler and will use more fuel. It is unlikely that it will reach mormal operating temp unless you do as lake sailor suggests and remove the working parts of teh thermosta. if you use the boat in the winter it will take an age to warm up if at all properly. for the increase in fuel cost you would easily be able to buy a thermostat. If mercruiser thought it didn't need one they would have left it out!!!!!!!!
 
I would only do it as a emergency measure, i.e. to get you home etc. the engine is designed to have a stat, so you should have one fitted. Hell they are not expensive! if you are that concerned fit a new one every year!

Medskipper
 
I've just discovered (and corrected) that my 135 hp Mercury outboard has been running with no thermostats (for at least 2 years). Put some in and it runs a lot better at low revs.
No adverse problems without them though.
 
I fitted 2 last year!
The cost is peanuts. BUT, when the bloody thing shuts down (For the second time in 2 months) you get a bit Pi**** off.
Don't really want to be changing stats anchored in front of a big ferry again!! Yes, I know they should be there. Yes, in a perfect world, I would run one, but it's causing me problems!!
Coments like 'mercruiser designed their engine to have one', so it should be there etc is a typical coment from some **** who has never had a problem.
I just want to know if it safe to run my engine without one!
 
Drill a ¼" hole in the thermostat body. This will allow some water to circulate all the time. Warm up will be a bit slower but gentler on the engine. If your thermostat starts sticking you will notice a slower rise in temperature. It may not even overheat, just run hotter.
 
Mongoose - are you using genuine Mercruiser 'stats ? They're supposed to be warranted......so if nothing else you could shout at the supplier.

I bought my boat from a Mercruiser dealer. He was running both engines without 'stats, so I assume it's probably ok - but maybe only if you can claim the excess fuel you'll use together with getting a trade discount on any parts the engines may need sooner - possibly elbows and risers - as a Mercruiser dealer should.

(BTW, if it makes any difference to you, comments such as [ QUOTE ]
"a typical coment from some **** who has never had a problem.

[/ QUOTE ] "

as a relative newbie may not encourage too many people to offer helpful suggestions. You might not like his opinion, which is correct incidentally, but that's not really a reason to start hurling insults............... /forums/images/graemlins/wink.gif)
 
In reply I have had lots of problems with thermostats over the years and have always relaced them when they have failed. I also had a V6 O/B where one thermostat was stuck open and it ran a bit erractically at low speed once replaced ran perfectly.

at the moment i have a generator which has a iffy thermostat so it is out and i am waiting for a replacement to arrive so the thing runs properly.

Engines are expected to run at certain temperatures to save wear. fuel etc a piont that you should remember is the air/fuel mix is temp related as well so if you run it cold there could be an issue with spark plugsetc as these all temp related as well.
 
Quote
"what, if any engine damage could it cause?"

Because it won't get up to temperature it will suffer from "fuel wash" in the cylinders. The improperly atomised petrol will wash a lot of the oil off the bores leading to increased bore/piston/ ring wear.
Your call. Replace the thermostats or overhaul/replace the engine much sooner.
It's a no-brainer.
 
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