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obboy
01-14-2001, 02:18 PM
I have a '87 Ski Centurion OB. 200 hp Merc.
Powerhead built by Specialty Svc. in Burlington, CA. I installed a Temp. gage last summer. At WOT (6200rpm)the temp will continue to rise. Slowing to 4000rpm or less allowes the engine to cool. Water pressure is good and water flow appears to be fine. I tested the T-stats and they are good. They open at 140 deg f. I am concerned that there may be a lean burn proplem. While I don't have a flat spot or indications of fuel starvation, I can't figure out the temp problem. The fuel tank is in the front of the boat approx 18 ft. from the engine. Any one have any thoughts? If it is a fuel problem would a electric fuel pump help? What pressure setting?

Barry
01-14-2001, 05:16 PM
They should not get over 175. That is about normal. What are they showing?
Barry

obboy
01-15-2001, 04:45 AM
Originally posted by Barry:
They should not get over 175. That is about normal. What are they showing?
Barry

obboy
01-15-2001, 04:51 AM
I don't know. The temp gage is a merc unit. It has C on one extreem and H on the other with line indicators in between. If I continue at WOT I am sure it will peg the H side. I hit the overheat alarm once. However since I installed a low water pick up that has not been a problem.

D. Ulrich
01-24-2001, 02:22 PM
Barry, Install a new set of one piece cyl. heads! The old heads are two piece and will run hotter on the Merc.guage! Mine has the new style one piece 150 heads on it and runs about 3 quarters up on the guage at WOT. With the old heads it ran all the way up the H mark which was scary. You can get a used set of heads pretty cheep and also use the 2.4 performance head gaskets for a little more compression!

BillyD
01-26-2001, 03:47 PM
The water pump is the obvious place to start. Are you seeing good flow from the "tell-tale hole"? When was the last time you changed out the pump impeller? I had a temperature problem once on my old 1977 Merc 175 V-6. It turned out to be that the various water flow holes in the block, which can be seen under the "exhaust cover" (the tall vertical cover in the middle of the back of your engine between the two cylinder banks), had clogged. This is most likely to happen in brackish or salt water versus a crystal-clear lake, but is possible anywhere after years of use. This prevents the water from completing its flow path through the engine(thus preventing proper overall flow and heat removal). The remedy is to remove the cover and clean out the holes by twisting a small drill bit HELD IN YOUR HAND (do NOT use an actual drill to drive the bit). This will remove the gunk. Will need new gasket material to allow the cover to be replaced. While this job is pretty easy, be real careful with the bolt removal and re-installation. It is not too hard to shear one of these off. Need a sevice manual to get torque values, also. My mechanic buddy used to joke and say to give the thermostats themselves the "float test"; if they don't float when thrown in the water, then you don't need them! Obviously, he recommended throwing away the thermostats since they are only really needed in cold weather boating and can be a real source of trouble if they don't open when the should. I got rid of mine, and the engine still ran great (can always put them back if not satisfied). Good luck!

Barry
01-28-2001, 07:39 PM
Originally posted by D. Ulrich:
Barry, Install a new set of one piece cyl. heads! The old heads are two piece and will run hotter on the Merc.guage! Mine has the new style one piece 150 heads on it and runs about 3 quarters up on the guage at WOT. With the old heads it ran all the way up the H mark which was scary. You can get a used set of heads pretty cheep and also use the 2.4 performance head gaskets for a little more compression!
I run a new 2.5 drag. It hardly ever shows any temp as these motors are designed that way and have no thermostats.
Barry

obboy
01-29-2001, 05:14 AM
Thanks for all the input. I think I will try the heads. I moved from CA to North Carolina and am not hip to the used market for Merc Parts in this part of the world. Seems like this is OMC heaven out here. I'll check my sources back in CA. The 150 heads won't run too much compression will they? I don't want to run 32:1 Redline oil or AV gas. Currently my stock 200 heads have been shaved to 35cc. I run premium with Quicksilver oil through the standard oil injection pump.

FCnLA
02-01-2001, 10:55 PM
I would be careful of totaly removing the thermostats. They serve two purposes.
1. Stop water flow until the engine has reached operating temperature.
2. Restrict the water flow when open to keep a consistant flow of water.
What I mean on the second point is the water may flow too fast through the engine to make a proper transfer of heat from the engine to the water. They make restictors for this which go inplace of the thermostats.
Also you don't want to run AV gas anyway. It can cause some oils to separate because of the additives and is not suited for the application. FC

BillyD
02-02-2001, 09:28 AM
The reply from FCnLa about not removing thermostats may be "right on" in some applications; HOWEVER, as I said, I removed mine from a 1977 Merc 175, and it ran great right up until the time I sold it in 1999 (about 20 years of which was without the thermostats)! As I said, I did this at the advice of my Merc mechanic. He was recognized as one of the best on the east coast (if not the entire country). He later became a dealer rep. for Mercury serving several states. Everyone in the high performance area around here swore by this guy. I guess all I can go by is his expert advice and my own 20 years of flawless performance without the thermostats. Bottom line is that valves cause headaches (in boats, nuclear power plants and everywhere else they are used), and a straight flow path, with no moving parts, is always less likely to cause a flow problem. Though it may not always be the safe thing to do, many people also throw away there anti-siphon fuel valves for the same reason. However, as FCnLa states, if you need valves in a certain application, you need them.

FCnLA
02-03-2001, 09:35 PM
Billy D, I'm not doubting what you said. I don't have thermostats in my OMC, but I have restrictors (home made - take an old thermostat and cut the guts out and replace the outer portion). I do not use this boat in the winter. If it is cold or at start up I warm it up a while. The tolerances of the internals are set up to be at operating temperature. Unless one of his thermostats is malfunctioning, it should not be overheating.
So how's it coming obboy? FC.

obboy
02-13-2001, 05:07 PM
looking for those 150 heads. What's your fuel recomendation Barry? 92 should be ok don't you think. Keep in mind I still run the stock oil injection pump. 150 heads with the comp gasket won't put my volume under 35cc will it? The 200 two piece heads are cut to 35cc. Centurions aren't the fastest hull on the water so ultra high speed is not the primary goal. I run a 21 inch High Five Merc 5 blade prop at 6200rpm. This yields about 60-65 mph on the twin 80mph Airguides. I have a CMC jack plate with your basic setback (5-6in.)and a max lift of about 6". It's fun but it aint no Allison!!!!

Barry
02-14-2001, 05:34 PM
92 octane is the minimum for 35cc heads and 150 lbs max on premimum gas. It sounds to me your overheat problem has been solved now that you have a low water pickup. At high speed you were running out of water. You need a water pressure gauge to monitor your water pressure. Should have about 15 pounds at WOT. You never said if you have a nose cone or not.You must have one if you are jacking the motor up at all.
Barry

obboy
02-21-2001, 10:55 AM
I've always run a water pressure gage. The nose cone and low pickup went on after I hit the overheat alarm the first time. Water pressure has always been good and I get good flow out of the discharge tube, but the temp thing is still an issue. My visit with the overheat alarm was extreemly short term and and there is no apparent damage from it. Like I said it runs fine at crusing >4000rpm. It just gets concerning at WOT. Thanks for the input!