Engine water is very warm - new impeller kit, what next?

[SoCalBoatGuy]

1987 50HP 3 cylinder 0B162136. This engine seems to be running on the warm side. The stream from the telltale is fairly strong, but it seems to be hotter than it should. At idle on the muffs, it's about the same temp as a hot shower. I can keep my hand there, but it's hot. At 2000 rpm on the lake, it's too hot to keep my hand in the stream. I haven't taken it any higher for fear of overheating the motor. I've replaced the entire impeller housing and the impeller. I pre-lubed it with dish soap (as recommended by the parts dept.) so it wouldn't burn up on the first start. I made sure that the water inlet tube was seated properly up into the engine. It has the same good stream whether it's on the muffs or in a bucket.

When I replaced the impeller, I found lots of chunks of old impeller around the inside of the old housing. I'm thinking maybe there are some clogged cooling passageways in the motor. Does that sound possible? Where do I start to look for those?

I haven't been able to check the timing yet. I know incorrect timing can make a car engine run hot if it is not set correctly. Are outboards the same?

Any other ideas?

Thanks!

 

[GA_Boater]

You need to see if all the impeller chunks were removed. The water tube can hold some and some passages in the motor.

 

[SoCalBoatGuy]

Thanks, GA. The tube I can figure out. Where would I start getting access to the cooling passages?

 

[CV16]

Try to back flush the motor.

 

[GA_Boater]

Does this Merc have a thermostat? If it does, you can remove it and test it in a pan of water on the stove. Also you can back flush through the the thermostat access.

 

[SoCalBoatGuy]

Thanks for the responses, guys. No, it doesn't look like this engine has a thermostat. What's my next option? I can back flush through the top of the exhaust manifold where the tell tale connects. Would it get me more access if I remove the exhaust manifold cover and plate or the cylinder block cover?

 

[SoCalBoatGuy]

Hey Guys - just wanted to see if anyone had any other ideas for back flushing this thing out. I just don't know the best places to access the cooling passages. (BTW - I'm assuming I need to pull the lower unit off again so all the crap can come out of where the water inlet tube connects to the engine block.)

 

[SoCalBoatGuy]

No Title

Update - I back flushed everything as best I could last night. I back flushed the tell tale tube, into the block where the tell tale connects, into a water line around the exhaust plate, blew out the water inlet tube, took the screens off the water intake on the lower unit and back flushed the pump housing. I didn't have time to put the lower unit back on, so we'll see tonight if it made any difference, but I'm not expecting any change. I didn't see any chunks of impeller or anything else come out of the engine. Nothing seemed clogged up.

If this doesn't work, what should I check next? I still haven't verified the timing. I guess I'll make sure that is correct.

 

[bruceb58]

No, it doesn't look like this engine has a thermostat.

You have a service manual? I would be checking to make absolutely sure you don't have one.

 

[SoCalBoatGuy]

You have a service manual? I would be checking to make absolutely sure you don't have one.

Well, no, I'm not sure. Looking at a certain boat info site, it appears that there IS a thermostat. I'm not sure what part that is though. Is that the plate under the exhaust manifold cover?

boat info . no /lib/mercury/manuals/mercury_1965-1989_40-115.html#/46

 

[bruceb58]

Depends on the engine. On my 90HP it's on the top of the engine but I have a 4 stroke and it's a Yamaha head. Mine failed in the open position.

 

[Texasmark]

The classic 4 cylinders which were descendants of the old 25 hp Merc Hurricane 4 banger didn't have stats.

When Brunswick redesigned the mid range engines and looped them (after the OMC loop technology patent expired) they made significant changes in the line. One of those required the usage of 3 cylinders to get the "Loop Charging" loop (exhaust tuning) to function properly. As part of that upgrade a thermostat was included. The stat pellet has to be in the block's cooling water so the stat will be located somewhere around the block for that reason. Some engines have it sitting on top of the block and others as part of the water jacket cover where the spark plugs are mounted; 2 places of which I am aware on different hp engines, neither of which are the midrange triple loopers. On my '02 90 hp looper it, along with a pressure relief valve (more water at higher rpms for larger engine) were located at the upper left corner of said rear water jacket under a dual bulge (one stat and one relief valve) cover.

Disclamer: Some of the above is wild conjecture on my part, assumed to be true. I cannot attest to the validity of all of it but I am reasonably sure it's accurate or I wouldn't be wasting your time.

 

[SoCalBoatGuy]

No Title

Thanks for help, guys. There is no thermostat in this engine. There is a place in the exhaust baffle where some other models might have a thermostat and a poppet valve, but as far as the parts department and I can determine, this engine is not supposed to have a thermostat.

Man, I am really stumped on this. I blew all the passageways out with compressed air while I had it apart. Everything looks very clean to me. I don't know what to do next.

I had a little bit of time to put a timing light on it, and it's at 4 degrees after TDC at idle.

 

[SoCalBoatGuy]

Aha! I see in the parts diagram that there are supposed to be rubber seals between the water inlet tube and the top of the water pump. I don't have those. I guess this could make for a bad connection at the bottom end of the water pickup tube. I will fix that and see what happens.

 

[bruceb58]

I run a pressure gauge on my outboard. Does this have provisions for a pressure port?

 

[SoCalBoatGuy]

No Title

Good idea. There is a bolt below and to the left of the #1 spark plug that doesn't look like it's doing much. I could pull this off and see if it's connected to a water passage.

 

[Texasmark]

Thanks for help, guys. There is no thermostat in this engine.

There is a place in the exhaust baffle where some other models might have a thermostat and a poppet valve, but as far as the parts department and I can determine, this engine is not supposed to have a thermostat.
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The exhaust water circulation has to be maintained as long as the engine is running. No control mechanisms there.

The block cooling loop is a separate circuit for that reason. My closest reference to your engine is 1994 and it lists both thermostat and pressure control devices. I really doubt that Merc would completely redesign these engines as late as 1987 (when temperature and pressure controls were common in the industry) without these amenities, only to come back 7 years later and have an engine with them, not listed as optional, but listed as standard equipment. Makes no sense. Unless you have a piece of impeller lodged somewhere, your cooling passages look perfect to me, at least for the exhaust loop. Since you went to the trouble of pulling the exhaust cover off, why not go ahead and remove the cylinder water jacket cover too....spark plugs protruding through it.
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Man, I am really stumped on this. I blew all the passageways out with compressed air while I had it apart. Everything looks very clean to me. I don't know what to do next.

I had a little bit of time to put a timing light on it, and it's at 4 degrees after TDC at idle.
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My 90 triple is also 4 ATDC at idle and 20-22 at WOT, depending on how it's measured. On my 90, timing sets the idle speed at 675 +/- 50.

If you have a parts list showing a water pump outlet seal then surely that is a smoking gun. Water pressure is only a few pounds at the lower rpms and you have to force water up the tube and through the engine and "theoretically" force pressurized water against the stat and popoff valves.

 

[SoCalBoatGuy]

Well, good news and bad news. I pulled the water jacket cover off. There were a lot of impeller chunks wedged under the #3 cylinder. So, I think I found part of the problem. However, two of the bolts broke while I was taking the cover off. So, I'm spraying what's left of the bolts with PB Blaster while I wait for a new gasket to show up.

 

[Texasmark]

Well, good news and bad news. I pulled the water jacket cover off. There were a lot of impeller chunks wedged under the #3 cylinder. So, I think I found part of the problem. However, two of the bolts broke while I was taking the cover off. So, I'm spraying what's left of the bolts with PB Blaster while I wait for a new gasket to show up.

Sorry about the bolts but that happens a lot. I wire brush clean the threads on the bolts and run a tap to chase the threads in the block. Then use Blue thread sealer which acts as a lubricant going in, obviously locks the bolts, and makes it easier to remove next time.

The screw adjacent to #1 is probably for a water pressure gauge.

 

[SoCalBoatGuy]

No Title

Thanks, Mark. I got the bolts out. One came out with some vice grips. The other had to be drilled and then tapped. I took your advice and went ahead and ran the tap through all the other holes. It all went back together very easy.

I started it back up on the muffs and it is still running at the same temperature. The water out of the tell tale is pretty warm at idle. After taking all that crap out of the water jacket, I thought it would be a lot cooler.

As for the water pump washer and seal, they wouldn't fit. The new kit must have a redesigned collar for the water tube. It's a snug fit for the pipe - there is no way to fit the washer and rubber seal down into the hole.

I'll take it out to the lake this weekend and see if it gets better at higher RPMs.