98 Merc 200 EFI HELP PLEASE!

[TheTinMan]

At 3800-4000rpm and above I'm getting an overheat alarm (steady beep). Waterpump, thermostats and poppet replaced. What else could be causing this? Is it possible carbon build-up is the culprit? Don't know what to do....HELP! TIA

***UPDATE*** Today I installed a 30 psi water pressure gauge and also a Faria clyinder head temp gauge.

W tarmed up engine on muffs, starting peeing when gauge read about 100*F, went up to about 120* and would go no higher. Motor has 2 new 140* stats, is it weird that they opened when gauge read only 100*?? Tomorrow I'm going to water test it.

Do these temps seem accurate at idle and on the muffs? What head temperature should I except underway? What temp sets off the audible alarm?
Thanks

[Jay Smith]

Is your water pressure excessively high ? If so you have an obstruction ( somewhere) can be in the cross over holes at the exhaust divider plate , I just tore down a Drag Motor for a customer this week and it was FULL of water pump impellar parts. Also if you have a leak on the gaskets at the water pump as soon as the water pump gets exposed to the air ( boat gets up and running ) it will suck air and reduce the cooling water flow and the motor will get hot. The poppet bushing that is pressed into the block can be loose and following the plunger out and in and cause a heating issue too. That needs to be braded into the block securley and glued with yellow weather stripping. Have you also checked your timing ?And are your fuel filters AND INJECTORS clean and the fuel pump healthy with correct pressure , are your battery ( s ) HOT and in good shape to the engine?

Just a few things to "back yard" check and keep you and your wallet out of the dealership...

Good luck,

[TheTinMan]

Jay, thanks for the reply. Filters are new, fuel filter on engine and 10 micron filter/seperator. The water pressure gauge only goes up to 15 psi and it's pinned. What should the gauge go up to and what should pressure be? Poppet was done by Mercury tech. I replaced the waterpump base, gaskets and impeller and thermos. New plugs too. I had the same issue BEFORE the waterpump and poppet was replaced.

Timing may be an issue??? Motor seems to have a slight miss at low rpm's, when getting on it to get on plane you can feel it all of sudden run smoother, does this sound like timing? Not sure about injectors....how can I tell? Could it be a faulty temp sensor making it go off?

Will hooking it up to the computer at the dealer tell me anything?

Thanks a lot!

[Jay Smith]

Hooking up to a dealer computer will tell the history and give you an overall look at the health of the motor... If you have a heat gun shoot the bores especially # 1 its the hole thats the highest and most likely to have steam pockets if heating IS truely an issue. If the timing is stuck wide open it will run hot if sticking closed it will be LAZY and use the heck out of gas and smoke due to unburned fuel with a cold retarded spark.Check compression too may be blown head gasket. Does the water pressure pulse? Sometimes when there is a blown gasket the pressure will pulse everytime the piston comes to TDC and looses its compression into the water system. All I can think of now give me a night to sleep on it ..:rolleyes:

PS After reading your post again a pinned 15 # gauge isn't normal sounds like you have an obstruction in water flow. Does it peg as soon as its running or only at WOT ?

Good luck,

[props4u2]

A computer will not show any history on a '98 200. The only thing it can read is what is going on in real time, intake air temp, head temp, map, injector pulse width, rpm's,tpi range etc... Water psi should be 8-10 psi @ 4-5000 rpm's & 15-20 psi @ wot. You need a 30 psi gauge. As Jay stated, too much psi is a bad thing, & a loose poppet seat has fooled many good techs.


Lee

[TheTinMan]

Thanks. I think I need to check the poppet first. I was assuming it's OK since Tech did it. I know they did it becuase I have a bag of old parts when they did the work and see the gasket and a rubber diaphram, but maybe it's not seated correctly???

Pressure is about 3-5 psi at idle, at 3600 cruise the needle is pinned @ 15+ psi...sounds too high.

[The Big Al]

Pressure is about 3-5 psi at idle, at 3600 cruise the needle is pinned @ 15+ psi...sounds too high.

That pressure is perfect!

[us1]

You need a gauge that goes to 30 lbs. You could have 16 lbs or 40 lbs. you just don't know. 40 lbs is not a good sign.

[props4u2]

15+ psi @ 3600 is too high.
Listen to John, install a 30 psi ga.


Lee

[TheTinMan]

I'm going to install a 30psi gauge...should I also install a temp gauge? If so, what do I need besides the gauge, sender???

[shooter1]

I think the sensor in the port head has a temp sender for a temp guage in it. It has 4 wires coming out of it. I goes to the engine ground the 2 bullet connectors goes to EFI harness and there is 1 wire left. I would check to make sure it is really hot when it could be a faulty sensor.

Shooter1

[hsbob]

its the poppet baring any obstruction. you'll find the pressure will be about 30psi. buy a whole new poppet, dont waste time repairing the old junk. i hate to say it but welcome to the over heat club.

[sosmerc]

What is a "steady beep"? If it is a rapid, continuous beep I'd be looking at your oil injection system. If it is a steady, solid horn, then yes...it's temp related.

[TheTinMan]

sorry, meant steady horn, not beep.

I was ruling out poppet because Tech did it....guess I need to check his work???

[sosmerc]

To test the poppet valve: in neutral, slowly raise the rpm's while watching your psi guage, the guage should start to flutter or fluctuate noticeably between 1800 to 2200 rpm as the poppet valve opens and closes. (be sure to do this test with the engine submerged either in the water or backed in on the trailer...do not do this while running on a hose). Assuming your water pump is healthy, it should start lifting the valve off its seat easily before 2200 rpm. If you want it to open sooner, you can cut one coil off the poppet spring.

[TheTinMan]

***UPDATE*** Today I installed a 30 psi water pressure gauge and also a Faria clyinder head temp gauge.

Warmed up engine on muffs, starting peeing when gauge read about 100*F, went up to about 120* and would go no higher. Motor has 2 new 140* stats, is it weird that they opened whan gauge read only 100*?? Tomorrow I'm going to water test it.

Do these temps seem accurate at idle and on the muffs? What head temperature should I except underway? What temp sets off the audible alarm?
Thanks

[sosmerc]

Did the guage come with a sending unit, or are you using the "extra" tan lead that is available out of the port head sending unit?
The guage is designed to work within a specific ohms range...so how do we know the ohms range of the Merc Port sending unit is compatible with the Faria guage?
You could use a laser temp gun to compare the temp on the head at the sender and see how that compares with what the guage is indicating. Rarely are these guages very accurate.
As I have said before, running on a hose is not going to give you the results we are looking for.
Idling in the water I would expect the engine temp to come up to 130 to 140 and show 3-5PSI until the therms open. The pressure will drop some as the therms open. When running in gear, the pressure will increase as you give it throttle until the poppet opens, then it will drop suddenly and then continue to increase as you increase rpm. At WOT you should see 15 to 25psi depending on the speed of your boat. If you are just cruising around at say 3500 rpm your temp is going to be pretty cool....120 or less depending upon the temp of your water at the time you are running...and your pressure will probably be around 12-15 psi.
If you can get ahold of a good temp gun such as a Raytech, they can be pretty helpful in confirming temps on your heads. It is also interesting to point the temp gun at the base of each spark plug to see if you have much variation between cylinders. The guns that use a laser light for aiming are pretty neat for this, because they make it so easy to see exactly where the temp is being measured.

[TheTinMan]

After purchasing the Faria I realized I needed to install the Faria sender also, which I did.

I have a feeling the TPI may be off too, could this cause the motor to run hot?