Running without a thermostat...

moparlvr4406

moparlvr4406

Active Member
Jun 29, 2011
4,462
Lake Monroe Indiana Fourwinds H31
Boat Info
1985 340DA
1966 SRV180
(2)1960 Sea Ray 600
(2) 1963 808 Cruise-a-bouts
Engines
twin 350hp Crusaders 4.0 Onan /
Merc 950 SS
Merc 650
Merc 1100
twin Johnson 40
I have been having an issue with running hot
not to overheating but near the redline on a possibly inacurate really cheap guage
the heat issue was after long (45 minute plus) idle zone jogs and shorter (10-15 minute)
3000+ rpm runs.
also after the long idles the engine would bog if power was applied and sometimes long crank times for restarts
I installed a new Teleflex guage and sender yesterday and decided since I had never changed the stat
maybe I would for good measure and when I took the housing cover off ....there was no stat and looked like
there hadn't been one for a long time
the PO had changed the engine shortly before I purchased the boat and I wonder if he left it out due to the heat of breaking in a new engine.
anyway...would it be possible that my installing the correct 143* stat could cure my problems ???
guess I will find out next week but looking for some reassurance that it won't make things worse.
ran it on the muffs for about 40 minutes yesterday and it never exceded 140* on the new guage.
any input :huh:
 
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Alot of people on the river run with just the out ring of thermostat.They knock the center out of it.Sand would hang them up a lot.Moroso also sells aluminum temp washers for the same.I believe there is three in the pack. One for 140-160-180. They cost about 10$
 
I am assuming that the housing needs the restriction of a stat or some other "orifice" to slow the flow of water down long enough for heat transfer in the engine
is this a correct assumption ???
 
If you are already running hot with no stat than I think you have restricted or inadequate flow. Adding a t-stat will not solve this problem. Assuming you have an alpha, when was the last time you changed the impeller in the drive? Sounds like low flow to me.

Your t-stat is a variable orifice. Without one, the engine should take forever to heat up, and may never get there.
 
aqua*holic said:
If you are already running hot with no stat than I think you have restricted or inadequate flow. Adding a t-stat will not solve this problem. Assuming you have an alpha, when was the last time you changed the impeller in the drive? Sounds like low flow to me.

Your t-stat is a variable orifice. Without one, the engine should take forever to heat up, and may never get there.
Click to expand...
actually pre alpha MR drive with a new impeller
the reason I ask...I have seen this similar condition in the auto version
and the stat slows down the waterflow to allow it to stay in the block a little bit longer for better heat transfer to the coolant
as for forever to heat up...I can't really say due to a known inacurate guage...it started 1/4 of the way up when the engine was stone cold. It took about 15 minutes @ 1200rpm running on the garden hose to get the new guage above 120 with the new stat installed.
edit... and it appeared to have good waterflow out the back
when the new guage read 140 all 4 hoses were hot but not so hot that you couldnt hold them for awhile comfortably
 
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moparlvr4406 said:
actually pre alpha MR drive with a new impeller
the reason I ask...I have seen this similar condition in the auto version
and the stat slows down the waterflow to allow it to stay in the block a little bit longer for better heat transfer to the coolant
as for forever to heat up...I can't really say due to a known inacurate guage...it started 1/4 of the way up when the engine was stone cold. It took about 15 minutes @ 1200rpm running on the garden hose to get the new guage above 120 with the new stat installed.
edit... and it appeared to have good waterflow out the back
when the new guage read 140 all 4 hoses were hot but not so hot that you couldnt hold them for awhile comfortably
Click to expand...

do you have acces to a IR "laser" thermometer that you could use to determine true temps vice what the gauges (old and new) are saying?
 
Sometimes having no t-stat means the po was having trouble with overheating and took it out (which does increase flow). But like others have said, there's a possible problem :) Some engines are designed to need the "back pressure" of having a stat to feed water through all the back parts of the motor properly. And like the pp said, without one (in a normal non-overheating engine) you might never get it up high enough for optimal running.

Moroso also sells aluminum temp washers for the same.I believe there is three in the pack. One for 140-160-180.
Interesting idea, limiting the flow appropriately without the bottleneck of an opening thermostat. Of course, it won't help you warm it up.
 
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The bogging down after running for a long time at or just above idle could be caused by the automatic choke or cold start cycle engaging.
 
I concur with others. Overheating is not caused by not having a stat. Once issue is resolved you should use a working stat.
 
Sorry not to hijack your post, but has anyone seen seen a piece copper tubing pushed into the bypass port of the thermostat housing? I removed it because it was blocking almost all of the bypass flow. Based on what has been said in this thread it may have been factory installed, and I my need to put it back in. I just cant see blocking 95% of the flow on the bypass. It is a Merc 225 or the 302 Ford engine. I am not a gas guy. Give me a diesel any day.
 
Replacing the thermostat and fixing the exhaust flappers made no change for me. She runs a little hotter now. :(
 
I used a mico tv scope to check my drive and it was clear of debit. That is a cool piece of kit for working on a boat.
 
The stat seems to have cured the temp issue
Did my best to recreate the conditions that caused the hot running and never got over 170 degrees
about 160 at cruise.
 
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