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View Full Version : Exhaust relief & water pressue?



B.Mac
05-06-2001, 06:05 AM
Please help? Just bought used tweaked out Merc V-6 150 w/ nose cone LWP. Installed new impeller, and got decent water pressure as evidenced by good "tell tale" pressure. Also sprang various leaks all of which were stopped except between block & midsection on throttle side. I pulled powerhead, & immediatly noticed the mating gasket seemed different. It's a gasket covered 0.75 tin/metal w/ a series of holes aligning water port. I ignored it & placed a standard V-6 "blue" stock gasket, fired it up & immediatley noticed a dramatic loss in water pressure, barely getting any stream at "tell tale" nozzle. Opened thermostat covers (no thermostats found). Fired it up again and viewed very slow cascade of water runnung down waterjacket. Seemed all water being blown out exhaust relief holes (2 1" @ bottom of mid section and 12- 3/8" holes underside of midsection) My assumption is that the gasket/plate I removed, created restriction to keep the water up in the block longer, and that the old gasket was aftermarket or custom (looked aftermarket). At the expense of sounding green (which I am w/ modifications), can one of you old timers give me some insight into this situation & where I can get this gasket? Also, should I replace the missing thermostats? Logic dictates a cooler motor w/ reduced restriction of eliminated thermostats, but I'm wondering if too much flow allows for adequate heat transfer to coolant, and if thermostats create restriction to raise my water pressure. Two local merc dealers can't find any such gasket and look at me as though I have two eyeballs on the end of stalks like a lobster. Both told me there's no such gasket (the one in my hand) Frothing to run recently set up Vector, I did what any backyard motorhead would do... straightened out the old gasket, buttered it w/ RTV, and stuck it back in. Instant water pressure! Good "tell tale" pressure but little on gauge (pos gauge prob). Two questions please.. Where do I find aftermarket performance parts like this gasket and at what speed should a rookie driver level off at to avoid blow over or some other undesirable situation? Anticipate high 80's /18' Hydrostream Vector @180 HP LWP Merc Bobs cone, 6" setback on manual jack, 26 chopper & shaft even w/ pad.
Thanks fellas .....B. Mac

[Edited by B.Mac on 05-07-2001 at 06:04 AM]

Mark C.
05-06-2001, 09:46 AM
B. Mac -

Do you have a High-Perf Mercury dealer near you? Sounds to me like you have the high-perf gasket in there instead of the standard blue one. It's actually preferred and you can reuse it (did you keep it after you replaced it?). It's what I've been using. I don't know why you would see such a loss in water pressure just from the gasket difference unless of course you replaced it with the wrong one. What is your water pressure?