Need some advice on closed cooling troubleshooting, 85 mercruiser 170-gctid402871

[Guest]

bought this boat a couple months ago and did some repairs to the heads, it had broken springs and a broke push rod so I pulled the head to repair, it runs great now BUUUUUUUTTTTTTT when I add water to the riser manifold tank or whatever its called with the radiator cap it disapears in less than a minute then I add more water and it goes somewhere. I had the exhaust manifold and riser apart and they looked ok,no water in the oil whatsoever, that leaves the heat exchanger? I am also running kind of hot, how do you troubleshoot these systems and has anyone ever removed the closed cooling on one of the engines and ran it that way, I have never had a boat with closed cooling because I flush my engines for 45 minutes after running with salt water, everyone I know has had trouble with closed cooling so I have never wanted a boat with closed cooling.

I would prefer to just remove the closed cooling and make it raw water cooled, these engined came this way and have a lot of hoses run every where for cooling, any suggestions.

[Guest]

also anyone know where the thermostat is, I pulled the cover off the water pump housing and it wasnt there and didnt look like it would go there

[yachtman]

Do you have the block off plate in between the riser and the exhaust manifold?. May be a good time to do a compression check. Also when initially filling a motor it gets air pockets in it and can run hot until they fill up. If you javent put antifreeze on the other side of the thremostat that may be your problem.

[Guest]

I think Yatchtman is on to something, at least it's the first thing that came to my mind. Did you install the proper gaskets between your exhaust manifolds and your risers. Some have channels for your coolant to travel through your engines water jacket (block plates) and others are for raw water cooling. Yours is a closed cooling system and must use close cooling gaskets between the riser and exhaust manifold.

[Guest]

I used the gasket that came with the gasket kit I bought for the engine, was a complete rebuild gasket kit, it did come with a couple of different gaskets now that i think about it, i installed the one with 1 slot. maybe i didnt put enough water in it, do you fill it running, any idea how many gallons

[yachtman]

If it has one slot in it its the wrong one for closed cooling. The closed cooling gasket has no slots and a exhaust port hole only

[Guest]

yachtman wrote:
If it has one slot in it its the wrong one for closed cooling. The closed cooling gasket has no slots and a exhaust port hole only

really? I did not know that to state the obvious, so to clarify no water passages at all open up into the riser, could that be where my water is going also? doesnt seem like it, would that cause it to run hot

[Alaskanmutt]

If there is a slot then you are pumping your coolant out the exhaust.

Most would give thier first offspring for closed cooling.

I will give both of mine.

[yachtman]

Providing its a fully closed system yes no slots in the hasket and yes that would be where your water is going.

[Guest]

well I mickey moused a closed gasket temporarily, I had 2 gaskets, put the slots on different sides so there are no holes, used a light coat of ultra black on all sides and carefull tightened it back down. this is temporary because I have to take it back off when my exhaust flapper gets in and I get my new gasket. I dont think I would run it this way hard, just test to see if my water stays in and if it still over heats. I am going to let the sealant harden overnight give it a retorque and try it in the morning.

Just fyi i already did a compression check, I had 0 compression in the #2 cylinder and repaired it and then retested.

[Guest]

I filled it and it is holding water up to the cap, dont want to run it till the sealer cures though

[yachtman]

The gasket on the left is a gasket that would be used in a raw water / open cooling.system. the gasket on the right is the gasket that would be used on the closed cooling system. It blocks of the flow of water between the manifold and the riser.Keep in mind that these are gaskets for a small block 350engine so yours might be slightly different.

[img]/media/kunena/attachments/vb/706667=29996-2012-07-24_19-15-56_114.jpg[/img]

[Guest]

I looked at the a picture of the gasket I ordered with my flapper and it has 1 slot in it, looked up the part # online then looked at several websites and they all show 1 slot with the slot in the towards the bow. Does anyone with 170 or 470 experience remember a difference in the cooling system or what gasket it is

[2850Bounty]

bbruno wrote:
............... this is temporary because I have to take it back off when my exhaust flapper gets in and I get my new gasket. I dont think I would run it this way hard, just test to see if my water stays in and if it still over heats. I am going to let the sealant harden overnight give it a retorque and try it in the morning.

bbruno, just an FYI; running at slows speeds (i.e., not hard) is no guarantee that you will not encounter a back-flow scenario.

If you are doing this without the flappers in place, you'll want to know that there is still a risk.

.

[Guest]

The Merc 470 was a unique bird - take a look at this article:

http://www.sterndrives.com/470_coolant_leak.html