1985 Mercruiser 470/170HP motor with coolant leak through outdrive

most likely the heat exchanger has a leaking tube

Bt Doctur: most likely the heat exchanger has a leaking tube

Which tubes? Can you be more specific as to the location? This weekend, I am going to look for the leak again...thanks.

I am also working on a 470 found this artical http://www.sterndrives.com/470information/470coolantleakrepair.html.
My problem appears to be Head gasket. There is lots of stuff if you google it. I think the tube the other guy mentioned they are inside the heat exchanger.

simply filling the HX and seeing AF leak from the outdrive is not a head gasket.That bad of a leak would allow it to get into the oil. the HX is made from a series of tubes inside the HX. Remove the end cap and you will see them. If a tube is leaking there will be AF in the seawater side of the HX

A "new" mechanic told me that the HX is not needed as long as you run in H2O, and it can be bypassed. Sounds like a bunch of crap, but I don't know. Gonna check out the tunes as soon as I can as you mentioned to see what I can see.

If you mean run in FRESH water, true. HOWEVER, I would think that the labor to correctly replumb the system to eliminate the HE would exceed the parts cost for a repaired or even new HE. Would not trust the "average" mechanic to correctly redesign/replumb a HE system to raw. You can buy a fair amount of parts for a day of the average mechanic's billing rate.

RE: checking the HE tubes. Pull end caps which should be on the "raw water side". REmove the "radiator cap" on the HE. Fill HE full. Install a cooling system pressure checker ( low $$$ @ any auto parts store). Pump tester up to the pressure number on the "radiator cap", making sure first that its the correct one for that engine, check the raw water side of HE for sign of antifreeze. There shouldn't be any. If there isn't, you have a more serious situation. Find leak before you even dream about re-engineering/re-doing the cooling system

I worked on the HX today, basically filling up the coolant reservoir with H20, and without pressure testing (since I forgot to pickup the tool), and checked for leaks. I saw nothing dripping from the HX, but a few minutes after I filled the reservoir with H20, I had a 7 second drip coming from that single hole in the stern drive.... 10 minutes later, it dripped at 2 second intervals--and there was some residual green AF I could see...

I unscrewed the front end cap if the HX, but did not take it off...I did not want to chew up the gasket/o-ring--whatever was there...and there was no way for me to peek into the end of it anyway, but the fresh H20 dripped out of there too....telling me the HX tubes are leaking. Also, the HX was loose, and seem to have a connection on the block in the center of the HX with a rubber bushing which was very brittle.

Question: Should I pull the HX off, check out the tubes and try and get it fixed, or should I search for another HX, and replace it altogether? Can I drop some of that "radiator leak seal" crap in there and give that a shot first?

- Thanks in advance!
Chris

Depends... the MERC manual indicates that a small number of leaking HX tubes can be "fixed" by brazing both ends shut of the leaking tube. How many tubes you can do this to is likely specific to a particular HX application. Check Manual.
A good radiator shop should be able to do this for you. Get estimate from radiator shop first and compare to cost of a new HX.

Thanks Sandkicker,

Sounds like I gotta take the HX off and check her out. I am now looking for a diagram to see what the guts look like.

I took off the HX today, pulled the endcaps off and there was plenty of impeller-age in the front of the HX. It did not appear that there was any, or lots of corrosion or clogs. I sprayed through all the tubes, but ran out of light to perform the proper visual inspection.

The closed/AF side around the tubes was full of antifreeze, and I think there was a little AF inside the end caps--telling me leaky tubes. I will put it back on and pressure test it this weekend.

My next question is this: Assuming I have a leaky tube or two, would this leak drip out of the lower drive unit, from those 1/8'' holes BEHIND the fresh water intake on the stern drive? This would leave me to believe the leak is leaving through the fresh water intake. I don't think it would make it UP and out the exhaust as the AF, unpressurized, just can't rise that 1' to make it out the exhaust through the prop.

I guess it does not matter--a leak in the HX tubes is a leak that needs to be fixed. Also another interesting thing I noticed is that the in looking at the AF pipes-in and out of the HX, the front IN pipe, I could see nice shiny copper tubes inside the HX and the the rear OUT pipe, I noticed the copper tubes were somewhat oxidized. Perhaps the AF is not pumping through due to the impeller being shot?

What pressure are you testing the system?

The A/f cap is I believe 14 psi

I would check it at a bit higher, say 15-18 psi...

Jack,

I am pressure testing the HX directly. Plugged one side of the freshewater in/out and put the pressure tester on the other....I get up to about 16 lbs, but around 14/15 lbs, you can see a few tubes leaking. I picked up another one last night and I will test it tonight--hopefully it's in better shape than mine...

What i would do alsi is borrow a radiator tester. They have a adapter that connects to the cap fill location just like an automotive radiator and pressure check the entire system. That way you can see if there are any other leaks...

Yeah, will do. I picked up a radiator test kit from Advance Auto Parts....they let you "borrow" the tool by paying for it, and getting a 100% refund when returned....Once I get the HX tight, I will re-install it and test the system...I am sure there are more gremlins to find.

Thanks

I picked up a used HX, which went through a freeze and blew out the rear cover. I ground it down about 1/8", put a heeley coil into the threads, sealed the cracks with marine super duper epoxy, and she works. I consider this just a temp unit, and will eventually find another or get my original one brazed....I had a heluva time finding a radiator shop around here....and no mechanic/machine shop would braze them....

Thanks for all your help.

Resolved. Replacement HX with sealing/brazing did the trick.

just filling the HX and seeing AF spill from the outdrive is not a head gasket.That awful of a hole would permit it to get into the oil. the HX is produced using a progression of tubes inside the HX. Evacuate the end top and you will see them. In the event that a tube is spilling there will be AF in the seawater side of the HX