Cooling Question: SOLVED!!!

[kwoolard]

Re: Cooling Question: SOLVED!!!

bump^

 

[kwoolard]

Re: Cooling Question: SOLVED!!!

Anybody have any idea if the resistance value I got from the current sending unit I have is correct/compatable with the Teleflex gauges?<br /><br />Also, I removed the hose coming from my thermostat housing to the circualting pump and notice quite a bit of rust scale laying in the hose. I assume this could be building up in the risers I just cleaned and causing some flow restrictions. Any ideas how to remove the rust scale from inside the engine block with out flushing everything through the risers causing more build-up? As far the solvent that needs to be used, would standard radiator cleaner do the trick?

 

[kwoolard]

Re: Cooling Question: SOLVED!!!

I think that I may have found my overheating problem.<br /><br />Before taking the boat out of winter storage on its first trip to the river this year I decided to put some clear hose between the transom and the inlet to the thermostat housing and see what the water flow looked like while running on the muffs. I noticed that the water flow did not have much pressure and that it was very slow flowing. With the engine still running I got out of the boat and looked around the stern drive and noticed that water was flowing from somewhere that I hadn't noticed before. It seemed to be coming from the water hose connection between the transom and the bell housing (where water flows from the upper unit into the bell housing). Well I inspected further hoping to find a loose or broken hose connection and what I found was a 1/4" hole in the bell housing behind the brass barb fitting that the hose is connected to. Water was streaming from this hole, so no wonder I wasn't getting enough water at high rpm's!<br /><br />I took the outdrive off to determine why a hole would be there in the first place. It turns out the hole was caused by some sort of corrosion. Lokking from the outdrive side into the bell housing water inlet the aluminum was corroded away, almost 1/4" - 3/8" of aluminum was gone!<br /><br />Now I am faced with what to do next: <br />Should I replace the bell housing?<br />Use JB Weld to fill the missing aluminum and plug the hole or plug the hole with a weld?<br /><br />Where can I get a bell housing for this early model style outdrive?<br /><br />It is amazing as to how much material has corroded away in that one spot and nowhere else on the outdrive!!! And to wonder what boating in salt-water 100% of the time would do to one. I will post pictures as soon as I can.

 

[Buttanic]

Re: Cooling Question: SOLVED!!!

Brass and aluminum in contact with each other is a bad combination when it comes to causing galvanic corrosion. The Coast Guard recommends using a 300 series stainless fitting as a buffer between aluminun and brass when connecting to aluminum fuel tanks. I don't know if that is what caused your problem but it's possible.

 

[kwoolard]

Re: Cooling Question: SOLVED!!!

I am not sure about the dissimilar metal contact causing the corrosion either. I do know that every replacement bell housing I have looked at, is supplied with brass barb fittings for the hose connection.<br /><br />Does anybody know of a place to find good used bell housings?

 

[kwoolard]

Re: Cooling Question: SOLVED!!!

Well, after struggling through the overheating problem, I think I have somewhat put a good dent in it. It turns out that the hole in the water jacket of the bell housing was not allowing enough flow into the cooling system. I got a new one, replaced it and tried it out this weekend and the results are:<br /><br />Without a thermostat it ran about 130-140 at 3300 rpm's with a lower pitched prop than usual (15.25 x 15). As compared to last years trial runs at 165-180. However, keep in mind I am running in water that is now 55 degrees compared to 75 degrees last year when I had this problem.<br /><br />With a thermostat it ran about 175-180 until it blew the gasket that seperates the upper T-stat housing from the lower. Which I think may have been an installation error, not cleaning off the old gasket sealer good. <br /><br />It seemed to build up a lot of pressure in the cooling system with the stat in place, and also seemed as if the stat was opening too late. I checked it this year and it seemed to be fully opened at about 160-170. I thought that a 140 stat should be fully open at 140? Maybe just a bad stat this time? How much pressure is built up in these cooling systems?<br /><br />Also while running I had installed a clear hose between the water pump and the T-stat housing and notice a small bubble or two every second while running at 3000 rpm's. Seems I may have a very small air leak, but it doesn't seem like anything major. This wouldn't be enough to cause a drastic change in flow rate, right?<br /><br />Any comments? I guess I will try and replace the gasket properly this time and run it with the stat again as see what happens.

 

[QC]

Re: Cooling Question: SOLVED!!!

Thermostats are rated at the point when they begin to open. I know from memory, for example, that a 190 is fully open at 207. This is a truck thermostat, but again was used as an example only.

 

[kwoolard]

Re: Cooling Question: SOLVED!!!

So the 140 thermostat should be open fully at around 160?<br /><br />I just don't understand what else it could be that is making my engine run 130-140 without a thermostat!!

 

[tommays]

Re: Cooling Question: SOLVED!!!

with a 1974 boat that has been through a few owners a lot of times the cooling system may not even be connected up correctly<br /><br />i havent heard if you have a service manual for the motor but i would at least try to find something with the correct hose conections to be sure<br /><br /> it would not be the first boat that someone got creative with the plumbing<br /><br />if raw water pump is in good condition now the only other thing is that something is blockng the flow OUT of the motor which is also common on a 30 year old motor<br /><br />tommays

 

[kwoolard]

Re: Cooling Question: SOLVED!!!

I have a manual and have been using it extensively. The plumbing is correct, as I have checked over and over with all flow diagrams I can find. I have even posted it on this site before and recieved a response indicating correct plumbing. The only thing I can think of is scale build up inside the block itself. However this engine was rebuilt not too many years ago, maybe 6 or 7. I can't imagine scale building up and collecting in water passages this early in its life. I guess anyting is possible though. It did sit for about 2 years untouched after that though. <br /><br />How do you get in and clean the inside water passages without disassembling the motor from head to toe??

 

[Don S]

Re: Cooling Question: SOLVED!!!

You've been fighting this problem for 10 months, don't you think it's about time to have a pro look at it?

 

[kwoolard]

Re: Cooling Question: SOLVED!!!

I have talked with two certified mercruiser mechanics and one says to clean the risers and manifolds and more than likely the blockage is in the engine water jackets. <br /><br />Which makes sense, but what is the best way to clean it out back flush it from the T-Stat housing?<br /><br />The other certified mechanic, which screwed me over last year with some minor work (but that is besides the point), knows all about my problem and the things I have done to fix it. However, he says just run it without the thermostat.<br /><br />Which is the only way the gauge is showing it cooling, but it may not be necessarily cooling all cylinders. I would like to get it cooling the way it should be..........With a 140 thermostat and engine temp about 160.

 

[tommays]

Re: Cooling Question: SOLVED!!!

the only next step is to temp the hoses that would go from the block to the manifolds and risers and run the water overboard<br /><br />and then hook up a second supply of water to the manifold/ riser so that you dont melt down the exaust system <br /><br />this will allow you to see if the engine or the manifolds/risers are causeing the flow problem<br /><br /> i have seen people have the heads "boiled out" to remove the scale but IMHP if its that bad in the motor block its time to retire it<br /><br />tommays

 

[trog100]

Re: Cooling Question: SOLVED!!!

"I thought that a 140 stat should be fully open at 140?"<br /><br />a common misconception.. a stat should never be fully open.. if it is.. there is flow problem elsewhere..<br /><br />u have flow problem elsewhere.. finding whats causing it aint that easy thow it seems..<br /><br />trog100

 

[kwoolard]

Re: Cooling Question: SOLVED!!!

I understand that I have a flow problem, and it is probably in the block, being that I have just had the risers and manifolds off for cleaning. <br /><br />Does anybody know of the best way to go about backflushing the engine, and if there is a chemical I could run through the engine that may help dislodge any rust flakes or other particles blocking some of the small water passages???<br /><br />Tommays, I'll try that method to isolate the problem.

 

[kwoolard]

Re: Cooling Question: SOLVED!!!

Well, it has been a while since I have revistited the cooling problem that I am having. However, today I rigged up some clear hoses througout the plumbing system of my cooling system.<br /><br />I had a clear hose on the intake to the thermostat housing, one between the thermostat housing and the exhaust manifold entrance, and one between the exhaust manifold exit and the entrance to the t-stat housing cover.<br /><br />The result was no air bubbles from the leg pump to the t-stat housing(rules out the pump). There was a steady stream of bubbles in all other lines. <br /><br />Which I assume indicates one of the following:<br />blown head gasket<br />cracked head<br />cracked block<br /><br />However, with a cracked block I should see water in the oil. Before and after an oil change there was no sign of water. With a cracked head or blown head gasket I figured the engine would run rough, but it runs great and starts great. <br /><br />Are my assumptions correct or could it be something else? I guess next I should perform a compression check to isolate which cylinder bank it is coming from.

 

[Don S]

Re: Cooling Question: SOLVED!!!

Was the boat in the water when you did the test?<br />If it was just on the hose/muffs, you will get all kinds of bubbles.<br />Second question, it this an Alpha type drive with the pump in the drive?

 

[kwoolard]

Re: Cooling Question: SOLVED!!!

Don<br />The boat was on the muffs, however, I saw no signs of air bubbles on the clear incoming water line from the leg pump to the t-stat housing. Where are the bubbles coming from if none are getting in?<br /><br />The drive is a Pre-Alpha, Type 1.

 

[Don S]

Re: Cooling Question: SOLVED!!!

Your raw water pump may be the cause of your problem. With the boat at rest and idling or running at rpm, the raw water pump is under water. When you get up on plane, the pump is out of the water. If there is an air leak around the housing gaskets it will suck air not water and that's why you get the overheat very quickly.<br />Bubbles on the pressure side when on the hose doesn't tell you anything about air leaks since the system is pressureized and would cause air to be forced out of the system, not drawn in.<br />And with the drive on muffs, there is no way you can seal it good enough to test for leaks. Try that clear hose in the water while running.

 

[kwoolard]

Re: Cooling Question: SOLVED!!!

Don,<br />I have had the clear hose between the leg pump and the t-stat housing inlet the last time I was out on the water. I saw a tiny bubble about every 5 seconds or so, not a steady stream of bubbles, while on plane at 3200rpm. Would that be enough to cause an overheat problem as soon as I get on plane?<br /><br />Also, while running on the muffs yesterday, isn't the pump still out of the water and able to suck air? <br /><br />I ran it for ten minutes on the muffs and didn't see a bubble until I give it throttle, indicating I was not supplying enough water with the hose and the pump was able to suck some air. However, I ran it about 1200 rpm for about ten minutes, wouldn't that purge out all air in the cooling system?<br /><br />Thanks for your help Don!