Can I run without a thermostat?

[marlinempress]

I have a 1985 omc 5.7L motor. I don't have a thermostat in it right now because it got messed up and I took it out. I figured taking it out would just let all water flow all the time and keep it a little cool, but prevent it from overheating....but now unless I'm idling, if I run for more than like 10 minutes or so it goes up past 220 degrees...Am I stupid and overlooking an important function that the thermostat does? Or is the overheating probably caused by something else?<br /><br />Thanks!<br />Matt

 

[DHPMARINE]

Re: Can I run without a thermostat?

of course yo can.It's your boat !<br /><br />When you remove the thermostat in any motor,cooling water goes thru the engine too fast.<br />Tthis can cause overheating.The thermostat keeps the engine at an even temperture.<br /><br />And slows down the flow,so the system can aborb the heat.<br /><br />DHO

 

[marlinempress]

Re: Can I run without a thermostat?

cool thanks for the reply! So that'll 'cause it to heat up that much eh? Guess I'll have to get a thermostat back in there...Anyone else ever done this?

 

[Boomyal]

Re: Can I run without a thermostat?

Originally posted by marlinempress:<br /> cool thanks for the reply! So that'll 'cause it to heat up that much eh? Guess I'll have to get a thermostat back in there...Anyone else ever done this?

Yep! <br />However if the installation of a thermostat does not cure your problem then you have other problems. Duh!

 

[Don S]

Re: Can I run without a thermostat?

Just one note if you have raw water cooling, it may overheat in some spots of the engine, and not overheat at the temp sender. So you may not be able to see the overheat.

 

[Uncle Dave]

Re: Can I run without a thermostat?

Can someone please explain how too much water flow can cause an engine to overheat???

 

[Don S]

Re: Can I run without a thermostat?

Well, Uncle Dave, DHP already did. The water passes thru the engine so fast there is no heat transfer. And heat transfer (Always Hot to Cold) is what is required to cool an engine.<br /><br />

When you remove the thermostat in any motor,cooling water goes thru the engine too fast.<br />Tthis can cause overheating.The thermostat keeps the engine at an even temperture.

 

[Uncle Dave]

Re: Can I run without a thermostat?

Greetings Don,<br /><br /> Then why is it that removal of any thermostat has always caused the engine to run cooler. Not good but it always does.

 

[Don S]

Re: Can I run without a thermostat?

Usually it's the rear cylinders that get overheated, the ones up front where the temp sender is usually sees cooler temps. So basically your engine temp gauge only shows the temp of the engine where the water never sees the heat build up, and you are fooled into thinking the whole engine is running cooler.

 

[Uncle Dave]

Re: Can I run without a thermostat?

Good morning Don,<br /><br />I can see that as happening. But not to speed of water over iron. <br />The motor is overheating, so the dude takes the therostat out. If the problem is a clogged riser or manifold, then water is now still restricted by the clog and the thermostate is out of the picture. NOW the input area receives cold water and since it is severly restricted the rear ones may indeed still be getting too hot.<br /><br />By the way not to derail this thread, but I have researched lots of threads on this forum and most never answer the dudes question about whats happening with an overheating problem. Sometimes it is because the problem is not adequately described, but often it seems the cooling system is grossly misunderstood. <br /><br />You have an excellent flair for describing how things work. So perhaps a primer for all on cooling and the pitfalls of troubleshooting the beast.<br /><br />Thanks,<br />Uncle Dave

 

[AdamB]

Re: Can I run without a thermostat?

I wonder how much water flow he is getting too... he should check the water impellor too I think.<br /><br />Whatever caused the thermostat to get damaged probably clogged up or damaged some other areas...even severe corrosion of the thermostat could indicate his cooling system is also severly corroded and therefore not effective.

 

[Scaaty]

Re: Can I run without a thermostat?

Originally posted by Uncle Dave:<br /> Then why is it that removal of any thermostat has always caused the engine to run cooler. Not good but it always does.

You might be thinking of a car closed system, where it is just circulated, and eventually will just run cool, as it is warmed up, then cooled off on the round trip. Stick the same motor with a steady stream of cold seawater going in, take any radiater hoses off, and it will overheat. That cold water rushing over the cooling walls will NOT transfer heat at that speed

 

[Scaaty]

Re: Can I run without a thermostat?

Originally posted by AdamB:<br /> I wonder how much water flow he is getting too... he should check the water impeller too I think.

And I agree with Adam hear too...make sure any impeller, and circ pump are in top shape

 

[schwahn]

Re: Can I run without a thermostat?

Greetings Matt,<br /><br />I had a somewhat the same problem on my OMC 3.0L, it was overheating and this is what I did to fix the problem<br /><br />1) Check impeller for missing vanes and replace<br /><br />2) Loosen hose clamps and check for impeller vane parts that may be clogging or restricting water flow (I don't know how many hoses are on your engine, find out from the other experts here if you have to "prime" your cooling system after doing this step<br /><br />My experience with this, I ran my boat without the thermostat just to check if my theromstat was not opening causing my engine to run hot (thermostat not opening). My normal operating temp range is about 165 to 175 degrees. Without the thermostat it hardly moved on the gauge.

 

[marlinempress]

Re: Can I run without a thermostat?

Thanks for all the help guys! One thing I did while out on the water was take off hoses to check flow. The input hose from the sterndrive seemed to be putting out a lot of water, the circulating pump seemed to be pumping quite a bit too, when I took the hoses off the manifolds though (at the manifolds) water came flowing out of the manifolds themselves, I was under the impression water is supposed to be flowing IN to the manifolds from the thermostat housing....??

 

[garycinn]

Re: Can I run without a thermostat?

Running too cool can cause sludge and moisture buildup -- all bad things in any engine, auto or marine.

 

[DHPMARINE]

Re: Can I run without a thermostat?

Matt,cooling water going too fast thru the system can cause overheating.Also if the water can't get out fast enough,it absorbs more heat than it can get rid of.<br /><br />Could be your exhaust manifolds or elbows (or something else ) are not letting the water get out of the engine fast enough.<br /><br />DHP

 

[marlinempress]

Re: Can I run without a thermostat?

Well I took the thermostat housing off and the exhaust passages were pretty corroded and had a ton of restriction, so I figure it was pretty much recirculating the same water for a while. I put a thermostat in and cleaned out all the passages. I'm headed down to lake powell this weekend so we'll see if it did the trick!!!! Thanks for all your help!<br /><br />Matt