Merc 170 3.7L Cooling System Question and Water Pump Repair

Hello, I am new to this forum and have read alot of posts on here about the cooling system woes people have with the Merc 170 and 470 stern drive engines. I am working on a boat ('86 Galaxy Apollo) which was handed down to me by family which has a Merc 170 3.7L engine, and hasn't been run in about 6 years. I have done the standard regular maintenance (spark plugs, fuel/carb treatment, oil change and filter) and had the starter motor rebuilt. She starts and runs, but the engine is heating up to 180C or so even though only idling for 5-10 mins. I have "earmuffs" hooked up to the outdrive freshwater intake and the coolant reservoir is full and not leaking (that I can find). My plan of attack is as follows:

1. Run engine with earmuffs on and disconnect cooling water hose to HX to see if it is pumping water.

2. Drain coolant and test engine coolant pump.

3. Replace thermostat.

Assuming that the water pump is the problem, I have a few questions. I understand the water pump is on the transom side of the engine (backside) from what I have read, but is it on the engine or on the outdrive? I have the PDFs available online for the engine, but nowhere on there is the water pump, so I am assuming it is on the outdrive? If so, how does one replace this? Do you need to pull the outdrive? I have ordered the outdrive manual and will get the engine manual. Do these manuals give step-by-step instructions on repairs? If there is a good thread existing that gives step by step instructions on the water pump replacement and/or outdrive removal, please point me there. I know I read one that had some steps listed, but can't find it! Is this a difficult process and can it be done by one person? How do you remove the outdrive and support it?

Another issue is that the exhaust hose is severed on its way out of the transom to the outdrive. Does this have to be replaced? I assume this engine exhausts combustion gases through the prop?

Lastly, where does the hot cooling water post HX exhaust from the system on the outdrive?

Sorry for all of the questions, but any help is appreciated. As I mentioned, I will be getting the manual in a week or so, but am trying to work on it over the weekend. If anyone has PDFs or anything of the process of replacing the water pump, I would appreciate having them!

Drewmeister...

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

I could not read all that. But what I got to:
180 C is 356 F. Now thats hot!!!!
When you turn on the garden hose, does any water come out around the gimble housing when its not running? Does any come out when its running? Pull the front smaller hose off the heat exchanger and see if there is water flow there. Id bet no. some place your hoses are plugged, probably before it even gets to the exchanger. Also you will most likely have to remove the exchanger and take off the end caps and clean out the tubes.

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

Manuals for the drive are in the adults only section. you can pull the drive off and test run the engine by inserting a hose into the water inlet hole.Impeller is in the drive and is normally there for 2 years used or not used.would think it needs replacing

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

Bifflefan, if I am not mistaken, the temp gage on the dash goes from 0-200C correct?

When I turn on the hose, I do not get leakage at the gimble housing. I will definitely open up the HX and clean the tubes.

As for my other questions, how does one replace the water pump IF that is the issue?

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

you need to split the outdrive. manuals are listed in the adults only section.most likely #6 for the drive.

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

Drewmeister said:

1. Run engine with earmuffs on and disconnect cooling water hose to HX to see if it is pumping water.

2. Drain coolant and test engine coolant pump.

3. Replace thermostat.


Lastly, where does the hot cooling water post HX exhaust from the system on the outdrive?

Click to expand...

I'll answer the easy stuff LOL
1) I would not do that, because that deprives the exhaust of cooling water and you can burn up your exhaust shutters and rubber engine exhaust bellows (all that rubber stuff back there).

2) Don't do that either. When it is running take a look at the lower starboard side of the pump. Is it leaking? If not don't worry about it.

3) Again, don't mess with it yet. Normal operating temp is 165-200 F, so you are OK.

On the muffs with it running, carefully feel the pipe going into the front of the HX. Should be cold (seawater inlet). That tells you you have flow coming in. Your water exits the HX through the aft outlet and the hose (should not be real hot) goes up to the exhaust elbow where it exits the engine.

The very first thing you need to do is replace the impeller in the outdrive to make sure you have good flow into the HX. Replace the impeller and housing both. Someone will give you a link to the manual

Go to Autozone and borrow the tools to do a compression test and cooling system check. If they are OK you should be in good shape

Here is a link to your engine manual: http://www.4shared.com/document/zTbCbkDD/Service_Manual_08.html

Welcome to the 470 owners club

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

All, I DID run the engine for about 30 secs with the hose disconnected and it is not pumping water. Terry, the cool tube is what I was checking for on the freshwater inlet and it was hot the other day, indicating to me there wasn't flow, I just had to be sure. I will look for the outdrive manuals. Bt Doctur, I assume when you say "split the outdrive" you mean pulling off the lower drive unit with the 6 bolts? Is the impeller in there?

Also, Terry, yes, I didn't need to ask that question as I had followed the cooling water outlet to where it feeds into the exhaust manifold. So I guess exhaust and cooling water both come out the center of the prop?

Thanks to all for your help. Gonna work on the outdrive while watching college football tonight. Do you think local boating shops would carry that impeller?

Drew...

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

Drewmeister said:

All, I DID run the engine for about 30 secs with the hose disconnected and it is not pumping water. Terry, the cool tube is what I was checking for on the freshwater inlet and it was hot the other day, indicating to me there wasn't flow, I just had to be sure. I will look for the outdrive manuals. Bt Doctur, I assume when you say "split the outdrive" you mean pulling off the lower drive unit with the 6 bolts? Is the impeller in there?

Also, Terry, yes, I didn't need to ask that question as I had followed the cooling water outlet to where it feeds into the exhaust manifold. So I guess exhaust and cooling water both come out the center of the prop?

Thanks to all for your help. Gonna work on the outdrive while watching college football tonight. Do you think local boating shops would carry that impeller?

Drew...

Click to expand...

Not at the 6 studs for just a water pump repair...the lower unit seperates right above the water inlets where you use the muffs. My outdrive (Gen II) has 4 nuts and bolts there. Make sure that you have the drive in FORWARD gear before you seperate.

Happy boating!

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

Rocky,, so you are saying to get to the water pump I just need to remove the lower drive (the vertical bolts and screws above the water intake rather than the horizontal 6 nuts on the upper drive)?

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

http://forums.iboats.com/showthread.php?t=288430

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

Drewmeister said:

Rocky,, so you are saying to get to the water pump I just need to remove the lower drive (the vertical bolts and screws above the water intake rather than the horizontal 6 nuts on the upper drive)?

Click to expand...

True...but there are a few more bolts to do, such as removing the trim tab. Your best bet is to get your hands on a service manual for your drive (Alpha, I assume) and go by the numbers. I know that there is a hidden bolt under my Gen II trim tab, that you can only see with the trim tab off. And I have a nut at the very front of my lower unit that is easy to see, but you have to be looking for it. Even a Seloc manual will get you through a basic water pump replacement. The drive manual may be available right here, but I'm not sure where it can be found...maybe someone will tell us.

Happy boating!

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

Yeah you need the manuals before you start. Basically you need to put the control to WOT forward (very important) and remove the hydraulic cylinders by removing the rod that goes through the back of the outdrive, then you remove the six bolts holding the drive on and pull it off. Once off you can split the drive and service the impeller. I recommend pulling the whole drive because it is easier to put it back together "on the bench" and you can service the u-joints and check the gimbal bearing and alignment. you will need to get a Mercruiser alignment tool, about $35 on e-bay. No other special tools needed. Good luck.

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

Thanks again to all. Got the manuals from the Adults Only section. On the lower unit, there are 4 bolts, 2 sunken and removed from underneath and 2 in "the gap". The 2 sunken ones were easy to get off with a socket, but the two in the gap do not seem to match any standard straight wrench sizes? Are they metric for some odd reason?

Drew...

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

There's also a bolt/nut under the trim tab, and another one all the way up front.

Check out these videos:

Separating the Upper and Lower Gear cases:
http://www.youtube.com/user/TcElectronicsMarine#p/u/7/kfpasFN_g8w

How to change a water imeller:
http://www.youtube.com/user/TcElectronicsMarine#p/u/6/0QC6_j2_wmA

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

Thanks Eric! The funny thing is the only bolts he didn't discuss the size of was the two in question! I have tried several different wrenches and none seem to be the correct size, but I do not have metric straight wrenches if it is a metric size for some odd reason.

Drew...

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

The parts book says 0.437 (7/16) 20. That would be a 11/16 nut. I think

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

I believe the nuts in question are 5/8 ths.....just went out and checked....5/8ths they are according to Mr. Craftsman.......

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

Disagree there on the wrench sizes....a 5/8" star socket works on all of the nuts you can get to with a socket, which is not unusual, because star socket wrenches can turn metric bolts and have a bit of "play" in them on smaller bolts , but using a straight wrench in a tight spot with very little leverage, 5/8" doesn't work for me. I had to use a 16 metric (which doesn't make sense, but it worked). BTW, if you take the "5/8"" nuts and put them on a 5/8" wrench, there is alot of play there!

OK, so now my main question, I have taken off the outdrive and replaced the water pump, seals, draw tube, etc. So how do you this guy back on?? I know someone (Terry?) posted that you should take the upper drive off to facilitate reassembling the upper and lower drive, and although taking the lower drive off like I did was fairly easy, getting it back on is a PITA!! How do you tell if the water draw tube is where it need to be, since i definitely can move and miss it's slot, unlike the gears?

Any help appreciated. Trying to finish this in the AM!

Drew...

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

Glad you found something to work for you....5/8ths worked for me and no rounded off nuts....and yes getting the two together is a PITA that's why the long guide tube on the w/p housing....if the water tube is straight and your eyeballs are close to accurate you won't have as much trouble as you are anticipating...careful and slow are the operative words....

Re: Merc 170 3.7L Cooling System Question and Water Pump Repair

Yes it can be a PITA, but you need to make sure of a couple of other things too. First you need to be sure that the control handle at the helm is WOT forward. That puts the upper and intermediate shift shafts in the forward gear position (pointing straight ahead). Next you have to make sure the gearhousing (that you are trying too put on) is also in forward. Do this: See that little splined shaft in the front of the gearhousing? Turn it all the way clockwise (looking from above) into forward gear and rotate the prop counterclockwise until it locks. Take a bungee and wrap it around the prop to keep CCW pressure on to hold it in gear. Now when you get the thing back together everything will be in the correct gear. Make sure the intermediate shift shaft stays pointed straight ahead when it slips back over the lower ss, and if you need to turn the driveshaft (long vertical shaft) to get the splines to line up, turn the prop CCW ONLY. Have fun