running without a thermostat?

[matt k]

Ok, so for the past 2 years, when i pull the boat out of winter storage it runs hot, like 180-190 underway, rising if you really open it up, be careful or you're going to overheat it hot. Impeller is recent and fine, old impeller wasn't missing any chunks. Thermostat is new too. Last year I backflushed the whole system several times, and just by some miracle the overheating issue went away after like the 3rd backflush. But it was a lot of dicking around and no obvious answer. The other thing I've tried is running without the thermostat in place at all. If I do that, the boat runs right around 140 rock steady.

So, I have a couple of questions: is it bad to run with no thermostat? Aside from taking a little longer to warm up?
Could it be that my water pump is on the way out, and with the thermostat out the impeller has enough juice to make up for the dying water pump? (the pump pulley doesn't rattle or have excessive play).
What else should I be looking at/for? I've flushed the headers, the transmission cooler, the hoses, etc. Found a lot of scale in the headers, but nothing else...

Otherwise, and with the thermostat out, the boat runs like a champ

[wotan2525]

Something is def. going on.... I ran without a thermostat for 5 years and the gauge never even moved. Getting to 140 without a thermostat tells me that your sender or gauge may be bad? Or that you have blockage in the system somewhere.

[sydneyACE]

I think maybe your gauge is lying to you. Either that or your engine's circulation pump is going-out.

Are your exhaust manifolds getting too hot?

I don't know first-hand how the cooling system on the Fords work, but usually, the impeller (raw water pump) isn't the pump that forces the water through the thermostat. On my system (Chevy), the raw water pump just picks the water up out of the lake, feeds it into the thermostat housing (distribution block, with all the lines) then forces it out the exhaust. The engine's circulation pump is the one that actually circulates the water through the engine (and through the thermostat).

You might be right about the raw water pump "helping-out" the engine's circulation pump, but it doesn't seem very likely to me. I think the water would just take the path of least resistance, which would mean skipping the engine all together.
I would definately try to trouble shoot the sending-unit/gauge, to make sure you really ARE getting too hot, before you spend too much time trying to figure it out.

As for running without the thermostat, it's not great for an engine. The oil never really gets up to temp. You will probably run rich too. (That is assuming that your gauge is wrong and reading too-high).

[Salty87]

infrared thermometers rock, harbor freight has them

[riveredge]

infrared thermometers rock, harbor freight has them

Agreed. This will take you from where you stand now, to being able to pinpoint a hot spot or even a left-to-right difference in flow, and help diagnose the problem. Not to mention it's better than using your hands to make sure everything is cooling properly for that first run of the spring. And checking lake temp. And the temp of your beer.

As to your problem, it does seem like you have a blockage somewhere, or else an inaccurate gauge. How did you go about "backflushing" the system before?

Also, a little tiny air leak caused by a loose connection between the lake water intake and the RWP can cause weird overheating, although more likely at idle...

[matt k]

well, i've been looking for an excuse to buy an IR thermometer for a while, so I'll definitely do that. The temp sender is cheap too, so I may as well replace that.

One of my risers gets hotter than the other. One is cool enough to touch for as long as you want, the other is hot enough that you can touch it for 10-20 seconds, but then it gets uncomfortable. Is that too hot? The IR will help me get better numbers for that. Also, where exactly do I shoot the block with the IR to get a good temp reading?

As for backflushing, I started at the raw water intake and moved up the line, removing each hose and flushing water from the garden hose in the reverse direction through each section, hoping that if anything was jammed in somewhere, I'd clear it out. This is the procedure my boat mechanic recommended. Maybe I introduced an air leak though, I will go back and tighten up all my hose clamps.

[sydneyACE]

When you're feeling the risers, that's without the thermostat installed?

If you can keep your hand on one of the risers indefinately and the other for at least 10-20 seconds, I would say that your raw water pump is working VERY well.

This further enforces the theory that either your gauge is lying, or your engine's circulation pump is going-out (considering you have already changed the thermostat).

Your raw water pump is doing it's job fine if it keeps the risers that cool. I think this also trashes the theory that you have a blockage in the system. (Unless that blockage is inside the engine.)

[matt k]

Well, that was my riser temp from last year when I had the same problem (with the thermostat out). I will check again this weekend when I should also have my IR temp gun and new sender as well.

The only signs of circulation pump failure I know of are leaks, a wobbly pulley, and poor cooling. Is there anything else I can easily check to see how healthy it is? I don't mind pulling it off, but if I'm going to take it off I might as well replace it. The extra afternoon of missed use is probably more of a loss than the $150 or so a new pump costs. The circulation pump isn't rebuildable, is it?

Thanks for all the help and suggestions.

[sydneyACE]

Those are all the normal signs of failure that I know of as well.
Yeah, I would definately try to diagnose it some more and narrow-down the exact problem before I started messing with that circulation pump. They're not too hard to change (not as easy as a Chevy :P), but I would do that last after I had checked everything else.

I'm sure it's possible to rebuild-it, but I have never done one. Might be more work than it's worth to save a few $.

[Scramblerone]

Im going out on a limb, but Id say your circ impeller has rusted away. Not a bad bearing that would cause a leak or loose pulley, but no circulation pressure to push through the thermostat. Pop it off and check it out, new gaskets are $3 and shouldnt take more then 30 minutes!