in-line 6 overheating problem

moneyhole

moneyhole

Member
Hey folks...I just got a 1977 V-20 cuddy with the Merc in-line 6 that was installed in 2008. It came with the engine that was pulled out as well - both are the 4.1 250 6 cyl. She has almost 3 hours on it and I went to perform all of my routine tests before I take the maiden voyage. Charge the batteries, plug in, and decided I better "yard check" it first. I put the water muffs on and turned on the water after I closed the two ports -one on heat exchanger and the other one on manifold. Boat fired right up but the temp guage started to rise after about 5 mins or so -160 then 200 then 220 - I shut her down. I saw one very small drip of antifreeze on a hose coming from the coolant fill. After it cooled down I opened the ports and nothing drained out. Do I start checking the stern drive water pump or the engine's water pump? Never owned a inboard with the heat exchanger set up before. Help would be great
 
Bypass the hose coming to the circulating pump and you can determine which is the culprit. Either circulating pump on the motor or the waterpump. I hate muffs and would probably dunk her anyway with a temp laser aimed at the sending unit. Amazing how many boats un cool in the water as opposed to out. When you pull the hose to bypass if it is dry inside you aren't getting water up from the lower.

Brian
 
Fisrt of all, I haven't seen many inline 6 motors with closed cooling, post up a pic of hte set up if you have it. If it hasn't been done within a year, go ahead and replace the raw water impeller in the lower unit. If the blades are broken off the pump, make sure you find them all. i wouldn't mess with teh ciruclation pump or the closed cooling till you know for sure you have good water flow to it. Odds are, its the raw water pump
 
Thanks for the help

Thanks for replying to my post so quickly. It has not been run but 3 hrs since 2008 - after the gentleman changed out the engine, prior to me buying it. I will click a picture of the 3" heat exchanger and coolant system tomorrow and see if I can learn how to post pics on this site. Like I said, with 60 psi on the muffs and opening the manifold and h. exchanger port and no water coming out at all, I suspected the stern raw water pump. Who is the best place to deal with on Mercruiser parts? I'm in Va - near Richmond. Thanks
 
moneyhole said:
I will click a picture of the 3" heat exchanger and coolant system tomorrow and see if I can learn how to post pics on this site.
Click to expand...

Open an account (free) on photobucket (www.photobucket.com). Upload your pictures to your account. Click on the pic(s) you want to show here. In the bottom left corner of the pic you'll see a box with various tag lines in it. Select the tag line that starts and ends with img. Copy that entire tag line and post it in your post here. (So it will look something like [img mypicture img] make sure you have the brackets [] before and after the img tag. That's all there is to it. Looking forward to seeing your boat.
 
I posted some pics of my boat-only had 1 of the motor. How expensive is it to have the lower unit water pump replaced if that is my problem? I have the in-line 6 with the heat exchanger and I'm not sure of which outdrive I have as it was painted over-completely with black paint. I had the muffs on -fired the boat and after 5 mins she climbed to 160, 180 200 then I shut it down @220 degrees or so. I let it cool off and placed a tub of water covering the intake lower unit holes and it bubbled some but temp still climbed. I didn't let it get anywhere near as hot and called it a day. I really want to fix her- it's been re-wired bow to stern, engine swapped in 'o8 with a known good running engine, but I did go thru the parts today and realized they used the old engine t'stat. That was cheesy. After it cooled down, I opened the drain ports & it had no water what so ever in the heat exchanger & I'm sure the manifold as well. What are ya'lls thoughts? Greatly appreicate them.
 
moneyhole said:
I posted some pics of my boat-only had 1 of the motor. How expensive is it to have the lower unit water pump replaced if that is my problem? I have the in-line 6 with the heat exchanger and I'm not sure of which outdrive I have as it was painted over-completely with black paint. I had the muffs on -fired the boat and after 5 mins she climbed to 160, 180 200 then I shut it down @220 degrees or so. I let it cool off and placed a tub of water covering the intake lower unit holes and it bubbled some but temp still climbed. I didn't let it get anywhere near as hot and called it a day. I really want to fix her- it's been re-wired bow to stern, engine swapped in 'o8 with a known good running engine, but I did go thru the parts today and realized they used the old engine t'stat. That was cheesy. After it cooled down, I opened the drain ports & it had no water what so ever in the heat exchanger & I'm sure the manifold as well. What are ya'lls thoughts? Greatly appreicate them.
Click to expand...

Price depends on if you do the labor yourself and what the condition is of the inside of your outdrive. I don't know exactly what the cost is for your unit, but from experience I can tell you that most impellers run around $20 and full impeller kits run about $50. Do a search on iboats.com. for your model.

On your heat exchanger comment, are you saying that the raw water side had no water in it, or are you saying that the fresh water side was empty? If it's the fresh water side did you fill it before you tested it? That part of your cooling system is a sealed system and should not have gone dry. If you didn't fill it, fill it and test again. If it's the raw water side, I'd suspect a blockage somewhere. My thinking being that even if your impeller was gone, the force of the water pressure coming through the muffs would have been enough to at least wet everything. Only a blockage would prevent the water from reaching the heat exchanger. Understand that this is pure speculation since I don't know what type of system you have, and you haven't posted any pics. At the very least you should change your impeller. (It's just good practice to change the impeller and the lower unit oil at the start of every boating season.)
 
overheating

Destroyer ,
I did post pics ..they are under my profile or something of that nature. I think I posted 5 or 6 pics but only one I have of the motor.
The boat's cooling system has water/ antifreeze mixture in the pressure tank, but was low on the overflow jug. After running the boat, there was no water at all on the two drain plugs the fellow I bought it from told me to drain down - one one the manifold & one on the heat exchanger. I thought with thelow. unit muffs have filled up at least one side of the system.
What do you recommend I do in sequence to perform checks, but not too cause any engine damage.
 
2 hours labor as a stand alone job, 1 hour labor when combined with an annual service. Impelelr runs around $30, I susually use the kit that cost around $50, If it needs an upepr housing, add another 20 to teh kit
 
no water

sparepats... are you thing , like you posted yesterday, that it is the stern pump. I have a lot on motorcycle experience, but no much at all on boat wet systems. Thanks for all advise
 
the water pump in those drives is a weak point, they only have to run dry for about 20 sec before they are damaged, they will also get brittle and break the blades off if they sit for long periods of time. Go ahead and drop the lower unit. Do a search on utube, there are probaly several videos of people doing a water pump on a mercruiser(I'm going to make a video of it one day), i'll give you two hints, drain the fluid out first, and put the gear shift in fwd gear before you drop the lower. Between Ferm, Skools and myself, we've probably explained it 30 times on here, do a search for water pump replacement
 
thanks for more info!!!!

Thanks....been looking at all the video feeds I can find on the internet. The manual's pictures are very hard too make out. Wish thet were in color instead of B/W.
 
When I put the prop & water intakes into the tub of water and ran the engine for about 2 mins, while watching the temp gauge, I noticed about a 1/8 or less handful of rust particiles from the prop exhaust. Got to thinking, if I see this much rust from a boat that has a new used engine swap but & only 7.5 (not 3 as previously stated) hours, what else am I going to find?
My biggest question is , should I fill the antifreeze tank to full and put the tub or water muffs back on and try running it again? Or should I just order a lower unit stern drive water pump assembly rebuild kit? What kind of bill would I expect to see from a boat shop --- labor wise, since I already know the impellor parts price
 
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Spareparts, what are the most important things I need to pay special attention to when dropping the lower unit and making the repairs to correct my water intake flow problem? Any special tricks/tips I should be aware of?
Thank you for your help.
Do you & Destroyer feel this is most likey my problem?
** Note - My boat pics are on my profile page
 
Destroyer,
That's where I'm lost. There was no water at all in the 3" round tube and no water in the manifold when I opened the drain. I do know they used the old engine's thermostat when the swapout was done. Could I have dual problems.... engine T'stat not opening at set temp and have a bad stern drive water pump impeller pump at the same time? I'm just speculating at this point. Thanks again for any knowledge shared...it's making me crazy
 
If you pull the inlet hose like I told you you could see if the lower unit pump is working. Like most have said it is probably the raw water pump, buy one and install it for good measure if it hasn't been done in awhile.

I have never seen a 3" exchanger on an inline six. You have any pics of this motor?
 
There is a pic of the motor on my album page, but you can't see the 3" round exchanger too good in that pic. I did measure it and it's 3" in diameter. I bought a complete stern water pump kit today...drained the lower unit just before the sun set and the grease/oil most lilely had water in it. It has that funky smell and is olive colored. If I reading the manual correct, I should be able to pull the lower unit without removing the prop. We'll see how it goes and pray for sucess!!
 
forget the water pump - bad news

I see now why my water pump is bad, as I was taking off the lower unit I noticed some areas that had been epoxied and painted over. Guess what, the whole trim tab casting on the upper half of the motor broke off. I traded the boat with a horse trader. Can this type of "pot metal" be welded or am I just up the creek wihout a paddle. I'm going to post a pic of it in my album. If any one has any ideas, suggestions, solutions or other ideas:cry: than sinking her, let me know. I've contacted the fellow I got the boat from asking to reverse our trade...doubt I get far with that one. Live & learn.
 
so all's not lost

Thanks - was hoping it could be welded, but it burns my rear knowing this guy sold it to me like this.....very good lesson learned..buy a boat on a warm day and insist the owner take you out for a test ride. Ha! I'll call on some old buddies that have welding experience and see who they can recommend. I guess it's time for a cold one and wrap it up in plastic.
Thanks again SP....this is a really great site!!!!!!! :beer::beer:
 
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