thermostat question

OK, I finally have my water pump problem taken care of with the installation of a new crank mount pump. It pumps fine as proven with the "bucket method" Went out for first time today. Water temp kept cycling up and down between 160 and 200. Finally heated up to point that I couldn't run it any more.

Obviously a thermostat problem. Came home took it out and engine ran fine without heating up.

Couple questions:

Is thermostat necessary. Does an old engine without any computer controls necessarily need to warm up? Will the choke not work right?

If thermostat is necessary, did I just buy a wrong kind? Its a standard auto (160) t-stat that matches the one that came out. I bought this one a few weeks ago when I was trouble shooting my overheating problem, so it wasnt the original cause. Are marine ones different?

Larry, Yes temp. regulation is needed. Try another T stat.

Tim - I installed what was supposed to be a 143 degree thermostat (from Skidim) in my boat on Friday, but the engine ran warm. Tested it on the stove with a thermometer and found out it was opening at 160, instead of 143. Where'd you buy your 143 degree thermostat? Thanks for any help. - Bert

The order was fine. The issue appears to be the thermostats themselves.

The PCM 143 degree t-stat from Skidim opens at 160 and a Sierra 140 degree t-stat I purchased locally opens at 155. Both were tested on a stovetop with a cooking thermometer and both seem to run the engine warmer than they should.

I've seen another post where someone said he tested several t-stats and only a couple of them opened at the advertised temperature.

In my case, the engine runs in an acceptable temperature range of 160 to 180. But when it gets to 180 after pulling a skier, an alarm goes off and it's very annoying. That didn't happen with the original t-stat when the boat was new.

Yes, they offered to take it back, but it's not worth the time and shipping charges for such an inexpensive item. I'd just like to find one that opens at the advertised temperature. Thanks.

I ordered my 140 marine stat thru the local napa..that way I could return it if needed.

btw...it started opening right at 140..

May start a riot here but here goes,I too have the crank driven RWPump and no circ. on my stroker. Also running a 140 thermo, temp stays at 130 till you work her then 140 on the nose.
For reasons that we will not disclose,I drilled a 3/16 hole on the flange of thermostat to drop some of the pressure.This in itself did not lower the pressure enough, used another method, this fix worked.
Bypass from the block to the manifolds,after this fix I removed the modified thermostat,3/16 hole in the flange,and replaced with new 140 w/ no mods...
Instant warm up but excessive needle swing,180 to 140 and back up.Reinstalled old modified thermostat and all is well.Takes a little longer to come up to temp,130 but the needle stays rock solid........

140 seems a bit cool. Shouldn't they run around 160 once warmed up? My 86 runs at 160 or 180 after a ski set.

Larry- Run the boat without a stat for a few times to see what happens.

Does your cooling system plumbing include a re-circulation hose from the t-stat housing down to the raw water intake? If so, try blocking that off. Had to do that with my 65- solved my overheating issues.

-Brad

I have the one on the left in now. The weep hole is on the flat part near the raised circle edge.

I think it's an 1/8". I'm glad I did it, 'cause it did away with the temp fluctuation.

Barracuda wrote: 140 seems a bit cool. Shouldn't they run around 160 once warmed up? My 86 runs at 160 or 180 after a ski set. Larry- Run the boat without a stat for a few times to see what happens. Does your cooling system plumbing include a re-circulation hose from the t-stat housing down to the raw water intake? If so, try blocking that off. Had to do that with my 65- solved my overheating issues. -Brad

Brad,

I'm still having cooling issues. Went out this weekend with old t-state back in after new one fluctuated between 140 and 190 eventually overheating. Old one did same thing. Next time out I am going to take out t-stat and see what happens. I may also try the weep hole idea. Are you suggesting blocking the large hose from the fitting atop the engine to the circ pump? Isn't that a fairly drastic change from design? Doesnt the circ pump perform some function? Why is it there if not, although I know Boat Dr removed his.

What is with the weep hole idea? Obviously not how these things are designed, why does that help and why should we have to do it?

Another question for everyone? Why would cooling system in its current configuratoin for years be fine and now not be working. Well, its not really in existing configuration as I replaced my original OMC RWP with a new crank mount. Plenty of water moving through it, as external components are staying cool. Just appears to be a t-stat issue now.

I'm completely flumuxed now and anxious to get it right before snow falls so I can just pull it out and go in the spring.

Tim, No better pics, but here is a diagram. It appears to pretty much mimic your diagram. What I believe is a second t-stat is integrated into the housing and like I said is not accessible. It appears to regulate flow to the manifolds although it appears to always be open. I can blow through it when its off the boat and water always pours out the back as soon as water is turned on.

When I was out fiddling with it friday, temp kept fluctuating. I took it easy so as to not let it get too hot. But, like last time I was out, after several up and down cycles, the engine would start running poorly at low speed, stall, back fire, not idle, start hard.... After I try the next two to three things (no t-stat, t-stat with hole and original spec'd t-stat (on order, due friday instead of the auto parts store standared 160 t-stat which it has always had and which I recently got a new one of) I may try to talk you into a trip down to sunny and beautiful Cape Cod to help me unravel this mess. I'm at the end of my somewhat less than vast knowledge of such things and must now call on a Grand Poobah to help me out.

Are you guys talking degrees celcius or fahrenheit?