1989 wellcraft 3.7 mercruiser running 195 with no t stat

[terryjoe]

hey guys im lost.ihave a 3.7 mercruiser with closed cooling that runs hot well hot to me. i changed the outside waterpump checked the hose from the transom to the heat exchanger hose from transom to the outdrive and no blockage or kinks.i can run it 4 hours at idel and ti will not go over 120 reve it up to 2000 or 2500 it will climb to around 195. this is on muffs. i took it to the lake and just cruising it wont get hot but when i thottel up to get on plane it rises fast. i shut it down at 200 . so i figure t stat took it out on the lake and it done the same.no water in the oil or oil in the water . oh yea when it heats up to 195 on muffs i can kill the throttel and in 4-5 min its cool again what am i over looking any help would shure be nice thanks

 

[Bt Doctur]

Re: 1989 wellcraft 3.7 mercruiser running 195 with no t stat

You really need a thermostat in there temps in the 165-180 are somewhat normal for fresh water cooled engines.what you describe
is a bad impeller in the outdrive. When was the exaust riser replaced?

 

[terryjoe]

Re: 1989 wellcraft 3.7 mercruiser running 195 with no t stat

i have no idea i just got the boat and am trying to get it going. already changed impellar. bellows boots.hoses.till i got it about a month ago it had sat about 4 years or the licence said 08. thanks

 

[stonyloam]

Re: 1989 wellcraft 3.7 mercruiser running 195 with no t stat

Pull the front end off the heat exchanger and check for blockage. Pull the aft hose off the exchanger and put in a garden hose and see if you get a good unobstructed flow through the exhaust elbow. If all is clear, put a thermostat back in and change the impeller and pump housing. Even if it is new you have been putting a lot of heat back there, and the housing could be damaged. Are you running 50/50 auto antifreeze? Might want to do a cooling system pressure check, you can borrow the tools from Autozone. Good luck.
p.s. Try not to run over about 1500 RPM on muffs, and never with the outdrive above the trim limit.

 

[terryjoe]

Re: 1989 wellcraft 3.7 mercruiser running 195 with no t stat

also how much water should come out of the inlet hose from the impellar to the voltage regulator i have a new impellar but i only got like a garden hose turned half on coming out of the hose where it connects to the v/r dident know if it should have presure or kinda flow ?????

 

[terryjoe]

Re: 1989 wellcraft 3.7 mercruiser running 195 with no t stat

thanks terry i will try that first thing in the morning like i said i am lost on how this cooling system works

 

[stonyloam]

Re: 1989 wellcraft 3.7 mercruiser running 195 with no t stat

Cooling system is pretty straight forward. Just like your car except a heat exchanger instead of radiator. The raw water from the impeller flows into a hose at the transom, along side of the engine, through a pipe on the voltage regulator (to cool it) into the front hose of the exchanger, back and forth through three sets of pipes and out of the aft hose up into the power steering cooler (if you have one) then up to the fitting on the exhaust elbow where it exits and cools the exhaust gasses on the way out. The engine coolant is sealed in the exchanger where it circulates around the tubes and is cooled. The the coolant enters the exchanger through the more forward of the rear tubes and exits from the more aft of the two forward tubes. The engine circulating pump is pretty simple, just an impeller bolted to the front of the camshaft. Basically there are two causes of overheating, either a faulty thermostat (which should be a fairly rare occurrence), or reduces raw water flow through the exchanger. Primary cause worn impeller or impeller housing, followed by blockage of the raw water flow in the exchanger (broken impeller pieces or other junk) usually found under the front cap of the exchanger on the starboard set of tubes, or blockage of the water outlet of the exhaust elbow. Basically if you have a maximum raw water flow through the exchanger you should have the overhating under control. Good luck.

 

[terryjoe]

Re: 1989 wellcraft 3.7 mercruiser running 195 with no t stat

update guys i have changed the impeller again. checked the heat exchanger for rust or blockage. took the raw water inlet hose off the heat exchanger and hooked the garden hose to it and i got a good stout flow out the two holes in the outside of the transom. this thing will still at 1500 rpm for about 20 min run up to 180 deg. run it on up to 2000 rpm it will go up to 195 deg. this is on muffs . i did notice that water coming out of the propeller was warm not hot and the water out the transom holes was verry hot any suggestions ?????????????

 

[artificialreef]

Re: 1989 wellcraft 3.7 mercruiser running 195 with no t stat

Brand new boat to you, you should do a compression test to get an idea of what your working with.

 

[terryjoe]

ready to give up..

ready to give up..

hey all i have a 3.7 mercruiser with a closed cooling system that is running to hot.So far i have changed the impeller still ran 195. tore it back down and put in a whole new water pump still 195deg. checked the heat excanger it looks brand new.took the hose from the outside to the voltage regulater off and hooked up the garden hose got plenty of water back out the outside transom out both holes . took out the t stat still on muffs it will reach about 140 at idle thats after about 30 min. bump it up to 2000 rpms it will go to 195 degrees. what the heck else is thare to cause this?i did notice that the water coming out the propeller is warm but the water from the transom is verry hot grabbing at straws i guess. any help would be verry nice thanks ahead of time.

 

[ktbarrentine]

Re: ready to give up..

Re: ready to give up..

Why are you starting a new thread on this? You already have a thread going with recommendations. One of the moderators will merge this one with your existing thread to remove any overlap or confusion.

http://forums.iboats.com/showthread.php?t=573363&p=3941019#post3941019

 

[terryjoe]

Re: ready to give up..

Re: ready to give up..

sorry i have checked the suggetions and read that if youre problem wassent fixed it mite be best to start a new thread sorry

 

[ktbarrentine]

Re: ready to give up..

Re: ready to give up..

Actually, the tip is: "If you have a question that has not been answered to your satisfaction in the archives, it is always best to start a new thread of your own. By starting your own thread, you will receive the maximum number of views by forum members."

That means that if you cant find an answer to your problem that has already been answered in someone elses thread (by doing research), THEN you start your own new thread... You have a good thread going on this problem already, and hopefully we'll help get the problem solved in that original thread.

 

[Maclin]

Re: ready to give up..

Re: ready to give up..

Is 195 degress an overheat temp for that closed system?

 

[terryjoe]

Re: ready to give up..

Re: ready to give up..

again thanks and sorry for the mix up

 

[Oshkosh1]

Re: ready to give up..

Re: ready to give up..

As I understand it, closed systems usually run warmer than fresh water cooled. I'd compare the gauge with an IR to confirm the accuracy also.

 

[Don S]

Re: ready to give up..

Re: ready to give up..

I merged the two threads together, makes all the information on the overheat problem all in one spot.

 

[generator12]

Re: ready to give up..

Re: ready to give up..

As I understand it, closed systems usually run warmer than fresh water cooled. I'd compare the gauge with an IR to confirm the accuracy also.

I'm with OshKosh on this. Can't say how many times over the years I saw lots of money spent to correct an errant pressure or temperature reading on an industrial process, only to find out LATER that it was simply a gauge malfunction.

Terry, if the gauge or sender has lost its linearity, it can read normally in one place and abnormally somewhere else on the scale. You would be well-advised to verify the temperature variances you're chasing.

 

[stonyloam]

Re: ready to give up..

Re: ready to give up..

+1 on checking the gauge. Also you just may not be getting enough water through the exchanger with the muffs when you are running at higher RPM. Time for another water test.

 

[terryjoe]

Re: ready to give up..

Re: ready to give up..

thinking of pulling the head. put it on the lake today after buying a i/r gauge and they read verry close to the same temp.