'78 35hp cooling issue....

[ahicks]

When cold, water appears to be pumping normally, with good flow from the indicator. Within a few minutes, water is reduced to a trickle coming from indicator, eventually stopping with some slight steam instead, and the engine starts getting hot.

Complete water pump is new, water pipe is snug on both ends, compression on both cylinders match, and this is a fresh water engine with no signs of corrosion. Engine is new to me so I have little history on it, though it does have some discolored paint indicating it's been over heated at some point.

Never seen anything quite like it. If nobody has any ideas, I'm getting ready to pull the head and the water jacket to see if there's blown (cooked) gaskets or impeller chunks blocking the water flow. Wondering if anyone has seen anything like this that could save me the trouble (exploratory surgery).

TIA, -Al

 

[heypawpaw]

Check your thermostat, it may not be opening causing overheat.

 

[oldboat1]

Think you have the right idea (checking and cleaning water jackets). You might first try pulling off the l.u., and running some water up the tube to see if a flush helps (engine not running).

 

[Rustywrench]

I would carefully inspect your inner exhaust plate. A stainless plate that warps when motor over heats. It pulls away at gasket edges allowing exhaust gasses to,enter the cooling system. That is why you get water at first. As motor warms up the system starts to leak exhaust gasses. Something these early 35s were known for after over heats. Look at the parts book for the plastic water tube guide under the powerhead also. Depending on how hot it's been those become restricted. They are NLA now, but show up on eBay from time to time.

 

[oldboat1]

^^ good info.

 

[ahicks]

Thanks guys. T-stat issues, and the scenario Rusty describes (or something similar to it) exactly what I was thinking. Thanks for reinforcing those ideas/my plan. Looking at the extent of the discolored paint, this engine hasn't been near as hot as some I've worked on. There's just enough to let you know it's been hot.

Will post back with findings if I find anything concrete, and results of all new gaskets and t-stat one way or the other.

Surgery (and gasket scrapping) starts this morning.... -Al

 

[flyingscott]

Did you put the key in the impeller.

 

[ahicks]

Did you put the key in the impeller.

Not going to ask how that came to mind, :lol:
but to answer the question, yes. Water flow is normal when cold.

 

[ahicks]

I would carefully inspect your inner exhaust plate. A stainless plate that warps when motor over heats. It pulls away at gasket edges allowing exhaust gasses to,enter the cooling system. That is why you get water at first. As motor warms up the system starts to leak exhaust gasses. Something these early 35s were known for after over heats. Look at the parts book for the plastic water tube guide under the powerhead also. Depending on how hot it's been those become restricted. They are NLA now, but show up on eBay from time to time.

You nailed it. That stainless plate is pretty warped. Replacements not available either - nothing I've been able to find anyway. I've been able to flatten it some. Wondering how much warpage I can get away with?

Wondering if fresh gaskets and high temp sealer (silicone?) might allow the plate to be installed with the ability to squirm around a little while remaining sealed?

Thanks, -Al

 

[Rustywrench]

You need a #319577 exhaust plate. Found one on the E bidding site. Just one!

 

[ahicks]

Further pondering led to a "let's go for it" approach. Messing around on the bench showed warpage is really nothing too drastic. I was able to flatten it by hand between the bench top and the cover plate. Bolts should be pretty effective with the fresh gaskets (I used high temp silicone on both sides of both new gaskets). It's together now anyway. Head gasket and t-stat both replaced while I had it all apart.

Noteworthy maybe, is that the condition of the gaskets I had to remove showed the engine had not "cooked" nearly as bad as some I've seen where the gasket material is hard as a rock and kind of "chips" off during removal. Though I saw no direct evidence of leaking, pretty comfortable with the "warpage caused exhaust leaking into water jacket" theory.

My workspace was like a sauna this afternoon, even while working directly in front of a fan.

My feet are not being held to any fires here, so I put off the testing until tomorrow. Supposed to be much cooler. Will report back with results.

Thanks so much for your research! -Al

 

[ahicks]

Sooo, that was a waste of time and gaskets. Wishful thinking did not fix the leak. It actually leaked worse! It was blowing exhaust smoke out the bottom of the cover.... :^)

Took your advise and did a search on that part number, which I'm sure I had done earlier, but this time I did find it. Bonus was the seller wasn't trying to get rich on it. Pretty reasonably priced I thought. Should have the parts for another try next week. Fingers crossed, will report back after the next test..... -Al

 

[racerone]

Testing in a bucket ?---If yes , is the water level 6" above the pump ??

 

[Rustywrench]

Don't forget to take a look at the water tube guide #321513 & grommet #302497. Grommet is very common part, but the guide is also NLA. Look to see if it is damaged/closed at the top/melted. Replace the grommet.
These parts don't give trouble if the motor doesn't overheat. The problems begin after an overheat & you don't get back to original condition. Things have to be put right or you will continue have issues. Hope that helps.

 

[ahicks]

Thanks much for the ideas. Some times that can make all the difference in the world!

Yes, testing in a bucket (tub). Water level should be plenty high enough (well above pump). Grommets at both ends of the water tube have been visually checked (top one best possible) and are in good shape. Verified tube is a nice snug fit on both ends.

Originally the engine was showing good water flow for the first few minutes. My thought is this should prove the pump's ability to deliver through open passageways. I have reasonable confidence nothing has changed for the worse there.

On disassembly this latest go around, exhaust leak was very obvious/very easy to see. It's pretty clear this plate is warped enough where the bolts just can't clamp it well enough to get a good seal. After seeing that, I'm embarrassed to admit I even tried... -Al

 

[ahicks]

Issue remains to be elusive.
I've been through the entire cooling system, going so far as to remove the power head. There are no restrictions in the water flow (inspection included replacement of the grommets at each end of the water tube), or exhaust which was inspected at the same time.

Water pump impeller replace for a second time.

Plate inside exhaust cover was replaced, and after problem still occurred without change, pulled that back down and replaced the gaskets for the second time.

Does the same thing with or without the t-stat (also new) installed.

New head gasket.

Here's the deal. It appears the exhaust gas pressure is building to the point where the pump does not have enough pressure to overcome it. The big hint there was when I left the side plate off the lower unit. The one used to access the shift shaft screws when pulling the lower unit. With that cover off and exhaust free to exit there, water just roars out the indicator and the upper exhaust vents. This proves to me the water passages are clear. I have visually inspected every inch of the exhaust system looking for anything in the way of a restriction and found nothing. With the shift shaft cover in place, water slows and stops from the upper exhaust ports (indicating there is no longer cooling water in the head), then a minute later, the indicator stream is reduce to a dribble just prior to quitting completely.

So I'm thinking the exhaust pressure is building internally to the point it's exceeding available water pressure, eventually entering the water jacket in the head (where the water is usually mixed with the exhaust), and after blowing all that out, it enters the exhaust cooling jacket on the side of the block and blows the water out of that - causing the indicator flow to stop.

And yes - this is happening with a new OEM impeller. Out of ideas, ready to sell the engine for parts. -Al

 

[oldboat1]

The exhaust cover is probably warped if the inner plate was. Might dress it like you would a head cover -- 400 grit wet/dry sandpaper on a flat surface. Rotate mating surface in a figure eight pattern until shine is uniform.

 

[racerone]

Water deflectors in place and in good condition ??

 

[ahicks]

oldboat1 - I was running on that line of thought for quite a while - until observing closely and trying to figure out why what I was seeing was going on. Current thinking is that if the exhaust was leaking into the cover, past that inner plate, I would not be seeing the pisser quit AFTER seeing the water stop coming from the exhaust outlets. The pisser is the last to quit.

I have sanded the cover flat though. Same as I would a head or the top of the cylinders where the head gasket seals. and with gaskets installed dry, there are no external leaks.

Also, I didn't mention the head seems to be running much warmer than the exhaust cover too. Exhaust cover is just luke warm - like the water in the tub. That was puzzling until I came up with the exhaust pressure over coming the water pressure theory.

Racerone - Not sure what you are referring to as "water deflectors"? Engine is being run in a tub, with water level at least as high as it would be when mounted to a boat..

Thanks for the ideas guys. I am totally stumped, which is pretty unusual for this old man.... -Al

 

[oldboat1]

Doesn't the water get to the pisser first? Tells you the pump is working (but not necessarily that water is circulating through the powerhead) (?)