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PaulO
08-28-2000, 03:15 PM
Anyone want to guess on this one:
I can run all day at 4000 RPMs or maybe even above that. When I go full throttle, the engine temp starts to climb from its usual 130 degrees and will pass 200 if I do not slow down. Pulling the throttle back creates an immediate decrease in temp. The old motor did it too and I figured it was a rust filled block. It is an Alpha setup so the suction on the hose thing doesn't account for it. New motor, exhaust manifolds/risers, circulation pump, raw water pump, hoses, thermostat. Appears to be plenty of water flow at slow speeds.
PaulO

GeneD
08-28-2000, 04:45 PM
PaulO,
My boat does the same thing too!
But I don't go up over 200.
And you are running a thermostat? What temp?
Also, the thermostat has two places it can go. One is correct for raw water, and the other is for fwc, I think.
I took mine out, and the thing runs great. Well it did before I blew a piston anyway.
Something is not right with your motor, that is for sure.
And you DID replace the waterpump in the drive right? Any kinks in the hose?
Also, I remember a little rubber washer on top of the water pump tube that solved my situation. There is one on top of the drive shaft too that is called a sling washer. Lake X says to delete it, but I put it on anyway.
It's a baffeling situation.

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GeneD
007
Melbourne, Florida

[This message has been edited by GeneD (edited 08-28-2000).]

PaulO
08-28-2000, 05:09 PM
Gene,
New pump in the drive. Replaced the rubber washer on the pump. New hose from the outdrive with a new rubber spacer thing. Thermostat is new and I think 140 degree. Don't know about alternate positions for the t-stat. I will look in the manual and see what I have. Is it satisfactory to run without a t-stat?
PaulO

GEOO
08-28-2000, 05:36 PM
Paul, Too lean or too much timing can cause extra heat? After you run hard, check the plugs. GEOO

GeneD
08-28-2000, 05:45 PM
Hey!
This is the problem!
I just went through this with my machine shop guy.
I sheepishly admitted that I advanced the distributer to almost 14 degrees, maybe more, I am really not sure. It was just an experiment and while the experiment was a success, that success was thrown into the sh*t hole seeing how my piston is shot.
I say yeah! Pull back on the timing.
I'm telling you, and if Madpoodle didn't say anything it would have never occured to me.
I have been running hot, and I have a new WP and no thermostat. It just HAS to be the answer.
The Thunderbolt IV ignition is computer controlled and the intial timing should not be screwed with. 8 BDC. PERIOD!
Also, the lousy fuel we are getting lately must have a something to do with it. I normally run 89, I will now use 92-93.
Thanks guys, I feel a bit better.
But now I am wondering if I should rip the whole motor apart and check clearances.
It n e v e r e n d s...
Grease up that camshaft guys, I'm bending over!
PaulO,
GEO has a point too, and while I've been a bit hard core lately, in my humble opinion, you need a bigger carb.
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GeneD
007
Melbourne, Florida



[This message has been edited by GeneD (edited 08-28-2000).]

PaulO
08-29-2000, 08:07 AM
My total advance is 32 degrees. I have just re-rodded the Q-Jet secondaries to the richest rod available. I will pull the plugs and check though.
PaulO

Ralph Savarese
08-29-2000, 04:03 PM
Paul put a great south bay strainer in the bottom thats what i dis no more temp problems .You instantly get sea weed in the bay
Ralph

BigGrizzly
08-29-2000, 08:13 PM
I really think the timing is where to start.In my boat-before closed cooling system- i had all the same problems that you and GeneD had. Low power running hot etc. I found some old racing notes from my old hemi. "restrict water flow for better heat disipation. Run hot -lower temp diferential=better heat transfer". I then ran it hotter with a 180 tstat. it ran hotter but more stable. Had to retard the beast to keep plugs in it. Now with closed cooling system I run motor at 195 deg, and everything is better. your carb with the needles pose a large problem- unless set up exactly correctly the needles drop slightly in rough water, causing poor topend and dirty plugs. the marine version of the Q jet has dampner springs. Still I had to trash it on my Jersey Skiff. ---PS I appologize if I offended any one with my capital letters in the earlier posts, my kid said that means your yelling.

Blewbyu
08-30-2000, 02:24 AM
I agree with the timing thing-but there is another possibility.I'm not familiar w/Mercs,but on a Volvo (raw water system),there are "O" rings on the water pipe that lift the water thru the o/d.If those O rings are disturbed when assembling the outdrive-the system will suck air and reduce enuf water flow at high rpm's to cause above malady.The Volvo has the raw water pump on/atchd to the engine vs. in the outdrive-ergo a much longer "suction" side.
2.Speaking of suction-large hoses on suction side of any system can delaminate and collapse inside and do same thing-but usually only occurs if throttle is opened suddenly.You sure couldn't tell at all from looking at the outside of the hose.Forgive this "Dept. of redundancy Dept" remark if this is what the earlier ref to "suction thing...." meant.
Regards-Jeff

RickR
08-30-2000, 04:23 AM
PaulO
Did you check(or replace) the short hose that goes from the drive to the transom mount? Sometimes they develop a kink.
Have you had a impeller fail in the past? Rubber pieces from the failed impeller can get in the cooling system and impede flow.
Have you checked flow? Remove intake hose at thermostat housing, fire the engine and see how much water is comming out. Should be a pretty good stream.


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RICKR
mailto:riggerb@aol.comriggerb@aol.com</A>

[This message has been edited by RickR (edited 08-30-2000).]

GeneD
08-30-2000, 07:25 AM
Oooooooo, Rick...Good one!

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GeneD
007
Melbourne, Florida

PaulO
08-30-2000, 09:54 AM
The hose from the drive to the transom appears to be new as are all the hoses. I have not looked specifically for a kink at a trimmed postion though. I will certainly check that. Impeller is new and there appears to be lots of flow out the exhuast at low speeds. I will pull the hose off the t-stat housing when I get it back in the water.
PaulO

RickR
08-30-2000, 10:28 AM
PaulO
Where is your water temp sending unit?Although timing can cause overheating in your case the timing should be "full in" way before 4000RPMs.
Is youre trim angle different between 4000 and WOT?
Is you X dimension high?
If it is install a clear hose in line with the fresh water hose and see if you're getting any air.
I've posted it numerous times but on a high performance boat engine a oil temp guage is a must. If you have a oil cooler,(if you don't,install one) the water temp will stay normal until the oil overheats (&gt;260) then the water on the engine side of the oil cooler is warm entering the engine.

200 is awfully hot, if you have cast pistons be very carefull http://www.donzi.net/ubb/eek.gif. Make sure she cools down before you shut her off. At least 5 minutes, to save the bearings.

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RICKR
mailto:riggerb@aol.comriggerb@aol.com</A>

[This message has been edited by RickR (edited 08-30-2000).]

PaulO
08-30-2000, 11:09 AM
Rick,
Temp sender is in the intake manifold. Standard x-dimension. No additional trim above 4000. Have oil cooler, no oil temp guage. The temp change is really too quick to be anything but a quick decrease in flow or an erroneous reading. Happens a moment after you pin the throttle and starts moving up fast until you back off and it then returns to normal just as fast.
PaulO

RickR
08-30-2000, 11:52 AM
PaulO
Normally a bad temp sender will read low (&lt;less continuity).
Is your engine getting hot? Can you put your hand on the valve cover and risers?

Since you had the same symptoms with the old engine;
Are your exhaust manifolds filled with rust or sand, restricting flow?
You said you replaced the impeller, what condition was the rest of the pump in?
Is the honeycomb in the oil cooler clogged?

If you drop the lower unit blow some air BACK through the freshwater system see if you get any trash or impeller parts.




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RICKR
mailto:riggerb@aol.comriggerb@aol.com</A>

PaulO
08-30-2000, 12:20 PM
Rick,
New manifolds and risers. Can't tell if the engine is hot since it cools down too fast. By the time I slow down, the temp is already halfway back to normal and there is no excessive heat that is apparent by touch.
PaulO

AVickers
08-30-2000, 01:43 PM
Put a good volt meter on it and see what the voltage does at very high Rs... I assume that the electrical system with both the new and old engines hasn't changed???

Might be that the regulator isn't quite right and the alternator starts putting out higher-than-normal voltage??? Higher voltage could cause the temp gauge to read high.

I'd certainly look for the simple causes first...especially if the "temperature change" is immediate. Seems to me that even punching it wouldn't cause an immediate spike in temperature -- just as letting off wouldn't cause an immediate decrease.

[This message has been edited by avickers (edited 08-30-2000).]

Blewbyu
08-31-2000, 03:52 AM
PaulO-Avickers may have something there.It should be "normal" to get a DECREASE in temp when you initially punch the throttle-the immediate infusion of cold water should cool the engine temporarily.THEN a gradual rise should begin(unless u are already at design temp).Thats the way all my boats have been as I began to think more about it.I just took the X-18 out this last hour to retest that earlier observation.It held up-punch gas/engine cools.Gradually returns to design temp-slightly higher if running WOT for more than a few minutes.You may have a voltage mystery going on-'specially since both motors have done same thing.I certainly would never have thought of it tho.....
Good Luck.Don't envy you trying to chase this thing down.
Regards-Jeff