Mercruiser 3.7 overheating??????

[vjcthree]

Hello

I bought a 1986 Regal 200xl empress it has a mercruiser 3.7 190hp with a closed cooling and a alpha 1 outdrive. I have changed the bellows impeller thermostat flushed cooling system twice and I am still running hot. It is up to 3/4 on the temp gauge. I wasn't sure if the gauge was good so I bought an IR gun and it is reading about 220 to 230 the heat exchanger is reading 150-160. I just ran this weekend and I thought I would take apart the heat exchanger apart and check it. There was an impeller fin in it. How can I check and See if this is the new one or the old one. I had it changed so I don't have the old one to know if it was missing a fin. I heard I could take the inlet hose off. How much water should I get from it? The other big problem I have it plaining off it takes forever and I need to really shift weight to the front to get it to go. I was thinking of changing my prop to a 17 from a 19. Any suggestions will help. I am getting very tired of this boat and the expense and time with no changes in the right direction. I am mechanically inclined so I can do allot myself but I need a good set of directions of a diagram. I would also need it to be cheap as the funds are well past gone for this boat. Again thanks

 

[YeboGogo]

Re: Mercruiser 3.7 overheating??????

How many RPM are you running?

I took the thermostat out of mine and basically ran the hose thru all the passages. I found some interesting sediment. (note the engine wasnt ever on)

You may want to check the power steering cooler (if you have one) often it gets pieces of debris caught in it.

 

[vjcthree]

Re: Mercruiser 3.7 overheating??????

OK update
I removed the riser and the whole heat exchanger today. They both looked great. I don't know where to look next, any help would be great. Missing great fishing time. If I put it all back together would I be able to use it, as is if I don't let it get over 3/4 heat?????? I am getting a new prop and Will get on plain faster will see if that helps too?

 

[vjcthree]

Re: Mercruiser 3.7 overheating??????

ok another update

I have change the prop to a 17 I also changed the riser. I ran better, plained off well, but all was not great. I was getting high temp readings on all of the engine componets execpt the thermostat that was right at 160. Everything else was still between 200 and 220, I would never let it get higher than that. I checked everything with a IR gun and the exchanger was reading 140-150. I could get the RPMS up to about 4500. I looked at the power steering cooler it was clean. I want to take apart the cirulater and checkout the impelar but don't know really what to look for. I am also thinking about changing the thermostat again. I was told a new one can be bad and not opening all the way, Should I go with a 140? If I put the hose in all the passages I would do it where the antifreeze would be? Should I go backwords of the normal flow? What else could it be? What else can I check? Why is nobody responding to me?

 

[guyaverage]

Re: Mercruiser 3.7 overheating??????

Its possible you may still have impeller pieces floating around. With the engine running at idle, momentarily pull the water tube off where it connects to the riser. You should get a good stream of water out. Blip the throttle a few times and make sure the water volume increases. Don?t do this for long, you don?t want to burn up the exhaust flapper due to lack of water.

Check the fitting where the water hose connects to the riser. If yours is screwed in way too far, it can actually bump up against the interior wall of the riser, impeding water flow. It would have to be wrenched pretty far for this to be the problem, but it is possible. Mine is only screwed in about 1/2 inch, a little more than a firm twist of the wrench after being hand-snug.

Check your thermostat. Put it in a pan on the stove and use a meat thermometer to make sure it starts opening at 160. I had a brand new Merc t-stat that didn?t even start opening to almost 180, brand new right out of the package. Make sure you have the correct type thermostat. If yours doesn?t have an "umbrella" on it (like a large flat washer on the bottom) then you have the wrong one and water is not going through the heat exchanger. The 470 used several different t-stats during its run, make sure you have the right one.

Check the water hose next to the bellows down on your drive. Make sure it isnt kinked. Check the hose from the transom (inside the boat) to where it runs to the heat exchanger (or your voltage regulator). Make sure it isnt kinked, collapsed, or pinched.

One of the best things to do, remove the heat exchanger, and clean it with muriatic (hydrochloric) acid. Home depot, Lowes, etc sells it for about $5 a gallon in the paint section. Be carefull, muriatic eats holes in clothes, and will make you scream for your life if you dare get it in your eyes. Don?t breath the vapor it produces, wear old shoes, old jeans, safety glasses, rubber gloves, and keep a running hose right next to you during the process. Take the exchanger off the engine, drain it and flush it with water, then completely fill the antifreeze part of it (the larger water holes) with the acid. Let it soak and for about 5-10 minutes, then drain it into a 5-gallon bucket, or a big plastic storage bin. Use your hose and flush all the acid out, flush it several times. Take a look inside at the cooling tubes, they should shine like a new penny if you soaked it long enough.

Next, turn the exchanger upright, remove ONE of the end-caps, and completely fill the raw water side. Let it sit for 5-10 minutes, then carefully drain it and flush with water. Make sure you flush it very thoroughly. Replace the end cap (make sure the gasket is lined up right). Put it back on the engine. This hole cleaning process shouldn?t take 1/2 hour and will make a world of difference if its never been done before.

Let us know how things work out.

 

[vjcthree]

Re: Mercruiser 3.7 overheating??????

Ok so who wants to buy a boat?????????? I had fixed the problem. It was the wrong thermostat. Thanks for the help guyaverage. I was able to go out for 2 good days on the water. We changed the prop pitch to the right size (17) it planed out well It was nice and cool the whole time the WOT was right at 4600 and 37mph everything was on the up and up. Then I went out yesterday. Took some friends out everything started out great an them whamo. What?s that smell?????? Why did it just get really hot? Only went from 1/4 to 1/2. Shut it down. Take the engine cover off and here comes the smoke. The lower exhaust connector is smoking and now ripped and spitting water out. Ok everyone to the bow Trim the drive look nothing stuck, ok who wants to help. I took the hoses off 1 at a time starting from the exhaust and looked for flow to the cooling system and nothing (never let it fully start). Ok let?s eat lunch and let the current take us back to the dock. Put boat on trailer and took inlet screen off looking for debris nothing. Now I see the hose laying there???????????? How did the inlet hose come off the outdrive? Who cares I didn't let it get to hot I still had water over the impeller so that should be good still. I hope the biggest problem is the exhaust connector. Ok let's reconnect the hose and try it out. Not even close. Lost a ton of power WOT was only at about 3600 and I could only get up to about 22-25mph. I took it home and put it away and was way to cranky to even look at it last night. Hopefully today I can go home and start looking for problems. What should I even start looking at? I figure it?s the head gasket and I have lost at least 1 cylinder. I was going to pull the plug and check them first. I need to make or buy a pressure tester. Please tell me some other things to look for. Thanks again

 

[stonyloam]

Re: Mercruiser 3.7 overheating??????

That sucks! Sounds like head gasket. Real quick test, at high idle, pull the plug wires one at a time to see if you have a dead cylinder, Then compression check and coolant system pressure check. Autozone will loan you the tools for free. Probably should replace shutter while you are at it. If you pull the head, might be worth it to have a valve job done, and hardened exhaust seats. Good luck.