running without a thermostat?

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 :|

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.

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).

infrared thermometers rock, harbor freight has them

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Originally Posted by Salty87

infrared thermometers rock, harbor freight has them

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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...

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.

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.)

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.

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 $.

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!

Can I use normal ford 351 water pump gaskets (like these: http://www.rockauto.com/catalog/rafr...&parttype=2148)? I love skidim, but they want like 20 bucks for the pair of gaskets :|

Actually, can I use a normal car water pump? Rock auto wants like $30 for one ( http://www.rockauto.com/catalog/rafr...&parttype=2208 ),while skidim's is more like $120. I guess I just don't have a clear idea of what parts need to be "marine versions" and what parts don't.

I see no reason to use anything other than automotive gaskets. They still do the same thing (keep water in the engine) whether they're in a boat or not.

Same thing with the water-pump. Just make sure to paint it if it's bare metal. Cast Iron rusts pretty-much instantly if it even sees water.

That skidim pump is bi-rotational, so that adds some cost. It doesn't specify, but it may have some brass parts or something to make-it more corosion-resistant for open cooling systems. (Antifreeze helps to slow corosion in automotive engines.) Even if it does last longer, you could buy 4 of those $30 pumps for the price of one of the ones from skidim.

I don't know much about Ford engines in boats, but I think you will be fine with automotive parts in this case. Maybe someone more-familiar with 351s can chime-in.

Not sure about the auto, but I just purchased (this morning) a new circulating pump from skidim. It is bo-rotational, but delivered to my door cost 132.66. I have an 86 351 PCM. It comes with a gasket, that is needed so you don't need to buy a new one and you use the same pulley you currently have. I should have it by Friday and I will install that night if time allows. If needed I will keep you updated on it if you want. Good luck.
**On a second note, I just looked closely at the pictures of each online. I don't know if its just the pictures, but look at where the pulley bolts up. The marine one from indmar has bolts on it. The one from RockAuto only has spots where you put bolts thru pulley an then tighten into the pump. Im not sure how much difference that will make, or how you can change it but thought I would throw that at you.

as far as the bi-rotational thing goes, does anybody know if the ford truck motors turn the pumps the same way my boat does? Maybe I'll ask this question in the main forum and see if any of the motor gurus know...

Do not use the automotive style water pumps.... They will not hold up to the sustained rpm of the marine engine. They will be fine for a while but eventially fail due to the bearings walking out of them. I too think this is where the problem lies.

As for the T stat issue..... There is something wrong. If your boat is in the water the manifolds should be more less cold to the touch. I would pull the waterlines running to the manifolds off and start the engine the water running out of the hoses must be massive amounts and equal. With the price of fuel where it is I would get her running correctly with the t sat in place. You will see a huge improve,ment in performace and effeciency.

yeah, I'm not thrilled running it the way it is. It seems fine, but I worry that there are hot spots somewhere and I'm causing damage. I should have some time this weekend to poke around a little more, disconnecting lines and flushing things out (again!). If I can find the gaskets locally, I'll have a look in at the circulation pump as well.

Small update: I replaced the sender and cleaned the contacts at the gauge. The sender didn't seem to make any difference, but cleaning up the gauge contacts dropped the gauge temp by roughly 10 degrees. With no thermostat, sitting at the dock with the boat running around 1800rpm or so in neutral, the temp gauge reads about 135*. With my temp gun I get ~105* on one riser and 110* on the other. Readings from various areas on the block are all around 100*. I'll take some more readings tomorrow when we go out and actually run the boat hard for a while. My gaskets haven't showed up yet, so I haven't had a look at the circ pump.

edit: roughly similar while running after an hour or so of wakeboarding. Block temps in the 115-125* range. Guess I'll go ahead and open up the circ pump when I get a chance, seems likely that that's the issue.

pulled the circ pump, compared to te replacement, and it looked fine. impeller was all there, with all blades intact. no shaft play or anything like that, so i put the old one back and will return the new one (boats are pricey enough without wasting money). I also replaced all rubber water hoses, since mine were looking kind of ratty, and i was thinking maybe they were letting air in. all of that and the boat still runs exactly the same :|

does anybody know how I can test the gauge? Can I read volts or ohms from the sender to the block, and compare that with the gauge reading? That's about the only thing I can think of that might not be working right, at this point...

Do you guys use any specific procedure to clear air out of the system, like you do in a car? I haven't been doing anything like that, just assuming the raw water pump will purge any air on it's own...

I'm also going to check timing when I get a chance. I seriously doubt that's an issue, but I know with cars if you set the timing WAY off you can generate a lot of extra heat, so I guess it won't hurt to check..


side note: the gaskets I ordered from rock auto (for a 1987 ford pickup with a 351w), the plate-to-block gasket worked fine, but the plate-to-pump gasket was different and interfered with the pump impeller, so I had to use the one that came with the replacement pump.

Any other thoughts or ideas?

I think you should try putting the thermostat back-in and then check all those spots with your infrared thermometer. (Just for a good reference.)

Try doing a google search on testing the sending-unit/gauge. The resistance in the sending-unit should change as the temperature varies. The gauge references that resistance and the needle moves accordingly. It seems-like maybe your gauge is displaying incorrectly. (Can't know for sure, but having a reading from the infrared might give-us a good idea if the gauge is reading correctly.)
The fact that your gauge says 135* while your block is about 100* (you could touch that with your bare hand right?) makes me think that your gauge is still reading high. I have no facts to support this theory, but I would think that the cast-iron of the block would be HOTTER than the water in the block.

Keep at-it. You've got us all wondering what's up now.
I don't think you're hurting your engine by running without a thermostat, but you are probably loosing fuel efficiency and your oil isn't really getting up to temp.

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Originally Posted by matt k

Can I use normal ford 351 water pump gaskets (like these: http://www.rockauto.com/catalog/rafr...&parttype=2148)? I love skidim, but they want like 20 bucks for the pair of gaskets :|

Actually, can I use a normal car water pump? Rock auto wants like $30 for one ( http://www.rockauto.com/catalog/rafr...&parttype=2208 ),while skidim's is more like $120. I guess I just don't have a clear idea of what parts need to be "marine versions" and what parts don't.

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Gaskets are fine, I use automotive gaskets for most marine uses, though not head gaskets or any other gasket touching raw water and containing metal.

Do not use an automotive water pump. Marine circulating pumps have stainless shafts, stainless backing plates, and bronze impellers. Automotive pumps typically use regular steel or iron and in those cheapy pumps the impeller is stamped steel. It will rust quickly.