exhaust flange leak?

[waughoo]

I have just completed a full hose replacement (fresh and raw) on my 91 Mk1.5 with the M35.  I still seem to be loosing coolant somewhere, but can find no leaks at any of my hose connections.  I've ordered a new pressure cap and recovery bottle (bought the expensive one from Westerbeke because... why not.  It's FANCY!) and will install that due to it not being present (recovery bottle).  One of the times the temp started to climb and I stopped the engine to check and fill the coolant, as I was adding water, a small amount of steam appeared from the aft end of the exhaust manifold near the flange.  I've read that the gasket back there also seals the coolant passages in the manifold.  Has anyone done this job recently and can share with me how much of a son of a brisket it is and perhaps any useful tips?  I've considered buying an induction bolt heater to allow the removal of the nuts on the flange.  Getting a torch on those will be hard let alone somewhat dangerous.  I'd LOVE to avoid removing the manifold, but I need to solve this leak as it seems to run for about 3 hours before I need to add some more coolant.  Thanks in advance.

[Stu Jackson]

https://c34.org/muffler-exhaust-riser-replacement-2015/

Alex, there are Tips & Tricks in my tech note, regarding both the nuts on the studs and the gasket.

[Ron Hill]

Alex : Look closely at the M35 engine parts as all of the engine flange articles that I've seen (and written) are on the M25 & M25XP engines. 

I just want you to be sure there isn't anything different on your 4 cylinder !?!

A thought

[KWKloeber]

Alex

See below for how the exh flange gasket covers the cooling passages behind it in the exh manifold.  Possibly you have a loose flange?
Do you have a sweet odor of coolant in the exhaust?

You might need to install 3 new studs, depending....
IIWMB if they come out easily, I would replace them along with the nuts if there's any sign of corrosion.
The flange, etc is the same setup as on the 25s.

Before you get into that project, have you pressure tested the Hx? If it's OEM at that age it's possible there's a pinhole leak between the two sides.  When pressure builds in the { edit colored damn you Seri} CLOSED system, coolant gets pushed over to the seawater side and eventually out the exhaust.  Been there, own the Tee shirt.

One way to extend the time is to motor with the pressure cap loose so coolant doesn't get pushed to the seawater side.

[Noah]

Ken— Quote: "Do you have a sweet odor of coolant in the exhaust?" Is that similar to "the smell of napalm in the morning?" 

[waughoo]

Before you get into that project, have you pressure tested the Hx? If it's OEM at that age it's possible there's a pinhole leak between the two sides.

The heat exchanger appears to be quite new (looks like the aftermarket 3" sold by catalina direct).  The exhaust manifold on the other hand looks quite rough on the inside.  I havent checked the bolts on the flange yet, but your suggestion to pressure test is a GREAT idea that had escaped my troubleshooting list.  I will add that to my list to check.  Thanks for the reminder.

[waughoo]

https://c34.org/muffler-exhaust-riser-replacement-2015/

Alex, there are Tips & Tricks in my tech note, regarding both the nuts on the studs and the gasket.

Excellent write up.  Thanks for all the archiving work you do Stu.

[waughoo]

So... I ran the boat for 10 hours on Sunday to bring it from Anacortes to her permanent slip in Seattle.  After a shaky start with an air bubble causing hot temps, we managed to run solidly all day at 165 degrees.  I had started to try and clear an air bubbles in the H2O tank lines thinking that's where they were (which there could have been), however, it kept running constantly at 180.  I finally decided after a lack of success with the tank lines, to try the large 7/8" line on the port side of the engine under the exhaust manifold: THAT did it!  There must have been about 2 or three significant bubbles in that line since once cleared there, the engine ran all day with the needle glued to 165.  I was pretty happy after that.  For yesterday's run, I left the cap off the "pressure" setting so it would run at just atmosphere.  We lost no noticible coolant in those 10 hours of running.  Now I need to put the system under pressure and see if it will hold.  I'm going to cross my fingers that it will as I'd LOVE to avoid dealing with that exhaust flange RIGHT at the beginning of the season.  I'll report back.

[KWKloeber]

And the problem with that 7/8" hose is that it's the return from the Hx to the coolant pump so if you're burping at the dock and the TStat doesn't get to open, there's no flow in it (well, just a trickle thru a 1/8" bypass hole in the flange of the TStat.)

I finally decided after a lack of success with the tank lines, to try the large 7/8" line on the port side of the engine under the exhaust manifold: THAT did it!  There must have been about 2 or three significant bubbles in that line since once cleared there, the engine ran all day with the needle glued to 165.

[Ron Hill]

Alex : I just observe that flange ?leak? until you finally figure out if it or the riser is leaking. 

You might squirt some Liquid Wrench/Blaster on the three nuts and start to help let it soak in with the heat of running the engine - just in case you do have to remove that flange!!

I'm not too sure if there is room to get an impact wrench in there (with extensions) if you do have to remove those nuts??

A few thoughts

[waughoo]

KW: that explains why it would run at about 1500 at 178ish but any further push would start to make it rise.  There must have been just enough heat soak in the bypass circuit to the tank and a small amount of water flowing through the small air bubble hole to get it to keep itself cool at that load.  I had filled and burped it twice, but that lower hose never presented a problem till that trip.

Ron:  it is possible that there is no leak at the flange.  The pressure test should tell me if I'm okay.  I found a place to rent a pressure tester today (local auto store that basically sells it to you for full price and then lets you return it for a full refund when you're done using it - no loss on their part if you don't return it!) and plan to do that sometime in the coming week.  If it holds 11 to 15lbs for a handful of hours, I will chock this all up to being just a collection of air bubbles that never made it out.  If it won't hold pressure, I suspect the flange gasket is the issue.  To your point of regarding the riser, the previous owner appears to have replaced that in the not too distant past.  Thus, I might have to commit to a sooner than failure exhaust elbow flange gasket replacement.

Thanks all for the thoughts and ideas.

[waughoo]

I pressure tested my fresh water system today.  I pumped it up to 18 psi and it held solid for the 45 minutes I had it under pressure.  So I'd say my flange gasket is okay.

In someone else's overheating thread recently, someone suggested to check the raw water strainer o-ring.  Mine was straight up not there!!  I've replaced it and it is sealed now, but I havent had a chance to really test the engine under a load.

I bought a coolant reaivoir and a new pressure cap (pressure tested my old one and it was not holding pressure), and now that I know the system holds pressure, I plan to install the resivoir and hopefully that will resolve any further issues.  I feel that it is slightly possible that the gauge sender is half out of the water with the header tank a bit low to allow for expansion and that might be why it is reading a bit high.  We shall see!

[Ron Hill]

Alex : I like to use the clear hose for the coolant recovery.  That way I can see it there happens to be a bubble in that line!!

A thought

[waughoo]

I got the coolant recovery tank installed yesterday.  Unfprtunately, when I removed the over flow hose that was already on the manifold, the brass nipple came with it.  Fortunately it wasnt too hard to solder/sweat the fitting back into the neck.  I have test run the engine and it definitely is less erratic as it comes up to temp, but I want to get an away from the dock run in for a while to see how it performes before I celebrate.  We should lnow after this weekend as we will be out and about.

[waughoo]

Okay folks, I have had an issue with high engine temps since I have owned the boat and had done lots of work (new oberdorfer, new fresh and raw water hoses, new sea strainer, expansion tank, T-stat...) and was still getting readings at about 178 or slightly above 180.  The engine was never acting like it was running hot (no steam etc) so I finally got a new laser temp gun and checked the T-stat housing when the engine temp gauge was reading 178.  The reading I got was 158.  I tried at a number of other places and confirmed the engine itself was at a reasonable temp.  I then opened the butterfly on the t-stat housing and out came nice un-aerated water with no bubbles.  The gauge still read 178.  I had some burping problems with the 7/8" hose from the heat exchanger to the suction side of the water pump.  I reached back and gave that a squeeze and a wiggle and noticed the gauge dropped down.  I went back to the engine and looked in that same spot where I grabbed the hose to see what else might be in that area and saw the "gummy plug" was RIGHT where I was grabbing the hose.  A quick grab and wiggle of that plug got my gauge reading moved down some more to about 170.  I suspect that I have a high resistance wiring connection for the gauge in there that is causing the issue!  I have ordered up some deutsch connectors and will be replacing both ends (engine and at panel) with new connections.  It is my hope that this will solve the issue of the engine showing high water temp!  I'm pretty excited to have sorted this out.  I wrote this as a note to others to give the gummy connectors a check.  Most other posts surrounding the gummy connectors I've seen point out that they are resolving charging issues.  I hadn't seen any that were talking about gauge readings.  Hope this helps someone out there.