Boat question/problem - PeachParts Mercedes-Benz Forum

cjlipps · #1 07-22-2008, 06:56 PM

I have a 1990 Sea Ray 180 with a 4.3 Chevy and a Mercruiser outdrive. It has overheated at idle ever since I have owned it. I have replaced the outdrive water pump, the engine water pump and the thermostat and have removed and cleaned the exhaust risers (not too bad) and installed new gaskets on same. At speed it runs fine and does not overheat. At idle it will climb steadily to the hot side of the gauge but will come down steadily as I increase engine speed in neutral. Nothing I have done to date has changed the situation.
I have looked at the check balls in the T-stat housing outlet and am wondering at their function. If they are not opening as designed will it run hotter or cooler? Or, if they are not sealing as designed will it cause a hotter or cooler condition? I can't tell from looking what the water path is supposed to be or what those check balls do. I thought about removing them thinking they restrict flow out of the engine but they obviously have a purpose or they wouldn't be there.
It's an open system using only lake water and of course the only salt water in my area comes from one's pores in this kind of weather.
Any help is appreciated.
Thanks in advance.
Chuck.

KarTek · #2 07-22-2008, 07:54 PM

My gut tells me your initial ignition advance may be set too low. The PO may have lowered it so they could run regular fuel without knocking... This is just a guess though.

Hatterasguy · #3 07-22-2008, 08:06 PM

Not terrible familer with raw water cooled systems like that, but it certianly sounds like you have a restriction. The water pump's are enough to move it at high RPM but not at low.

I'd probably start at the drive and blow some water through all the passages to make sure they are clear. You guys have problems with Zebra mussels down their?

Their should be a valve in the system somewhere to prevent water from coming back up into the exhuast in a following sea. Some Mercruisers do it with flaps, I have seen those break off and cause havic.

I'd pull those balls, run it and see what it does.

waybomb · #4 07-22-2008, 08:28 PM

Let's start here:

Have you had it out of the water and running on a hose at idle? What were the results? Does the temperature continue to be elevated, or is it where it is supposed to be?

If not, do so. Let us know the results. Hook the hose up to the pickup, at the point where the water is usually drawn in from.

R Leo · #5 07-22-2008, 08:55 PM

I suggest replacing the water pump. I had a 4.3 in a S-10 Blazer that ran noticeably hotter after I replaced a leaking water pump. I ran it for about 6mo that way, replaced the water pump again with an OEM part and it went back to operating the way it should have.

That aftermarket pump wasn't to spec or something...maybe you're dealing with a similar issue.

kerry · #6 07-22-2008, 09:14 PM

Some boat motors have a bypass thermostat system where the raw cooling water bypasses the engine until the engine heats up, then the thermostat closes and forces the water thru the engine. If your system is like that, the thermostat might be not closing enough and at idle too much of the water is bypassing the engine and going right back out to sea. The increased flow at higher rpm's could be forcing adequate flow thru the block.

cjlipps · #7 07-23-2008, 01:05 AM

Thanks for all the replies.
On the hose and muffs it will not heat up probably because I always have enough pressure to feed the inlet and am reluctant to try and cut back on the hose to the point I see a difference. IOW I'm probably feeding plenty of water through with just hose pressure and can't simulate actual zero inlet pressure lake conditions.
I read on another site a guy speculating that the check balls wear out and when they don't seal at low rpm it doesn't force enough water through the engine. This seems backwards because they let water out and into the exhaust riser. Any definitive knowledge in this area?
I guess I could've gotten a bad pump but the symptoms have remained essentially unchanged through all my changes so that makes me unsuspicious of that.
Hadn't thought about the timing. It runs really well though so I doubt that it's retarded enough to cause problems although it's easy to check and I do still have a timing light.

Don't know about flaps in the exhaust. This system has large square risers off the top of the ex. manifolds and the exhaust goes in the water under the outdrive I believe.
Thanks again for the ideas. I'll mess with it this weekend and all things will be considered. My motto is "If you don't know what it is, you don't know what it isn't".

SwampYankee · #8 07-23-2008, 07:49 AM

Chuck, have you pulled the risers off to see if they've become restricted? Has it always been a fresh water boat? I've got an '88 Seville mid-cabin with the same engine and had a problem with it running hot at idle the second season I owned it. When I pulled the risers I would venture to guess that they were at least 50% restricted with rust and corrosion in spite of it being a freshwater boat for at least the time I and the previous owner had it (which was 10 years total at that point). I probably should have replaced them but not having any cash at the time I just cleaned them out as best I could, bought some new gaskets, reinstalled them and ran it that way for two more years until I replaced them.

They were really restricting water flow and the extra hot manifolds and risers were adding heat to the block. It's run cool ever since. The only reason I checked them out was on a ride with my in-laws

I started getting a lot of smoke out of the vents due to some cooking exhaust hoses thanks to the insufficient water flow.

CSchmidt · #9 07-24-2008, 10:31 PM

Most boat conversions have a second water pump that actually pulls the water from the lake. It typically uses a rubber impeller inside this pump to suck the water into the engine and split it to the manifolds and traditional water pump. These things go bad pretty quickly ( annually).

Typical boats in NC run a 160* thermostat. If you have a temp guage that may give you a clue if you are getting enough cooling. It is typical to see a "hot" engine if you run a boat hard, then shut if off, there is a LOT of residual heat. These engines work a lot harder than a car on the highway. Try to restart it in 3-4 minutes and your temp may be over 200*. But should cool back down again. A way to lessen this is to idle for a few minutes after a hard run.

Lots of good ideas above. Take out your thermostat for a while and see what happens.

cdplayer · #10 07-24-2008, 10:45 PM

I had an older model Sea Ray. Loved it until I had to turn it over to my ex along with the house, etc etc etc.

Ahh yes. California.

Oh, sorry. Back to your question...I too had the Chevy engine with Mercruiser outdrive.
The engine is cooled by lakewater drawn in through the outdrive through a heat exchanger and back out to the lake. With this design, lake water never enters the internal passage ways of the engine. The engine has a closed system thus is protected from contaminants. IE mud,sand,fish, etc.

Your problem may be the impellar that draws the lake water to the exchanger.

compress ignite · #11 07-24-2008, 11:49 PM

If it's got a Primary Raw Water Pump (May be belt driven?) and you've never
changed out the Rubber Impeller...That will be a large part of your problem.
(You may also find impeller blades missing...And you know where they went)

Fresh Water Sailors may get away with an extra season of use out of the
W.P. Impeller...But if you're out on the Salt...You'll put a fresh one in every
Spring as part of your PM.(So easy to do on an Inboard or a I/O compared
to an Outboard)

The risers are a Rust Factory.

Hatterasguy · #12 07-25-2008, 11:15 PM

Guys read the post he did that. Also Merc's have a pump in the drive like an outboard. I have actualy never done one because I have always had Volvo drives. Volvo's only have a pump on the engine.

Impellers last 4-5 years, unless you run them dry or in silt.

SwampYankee · #13 07-26-2008, 09:51 AM

Any updates cj?

waybomb · #14 07-26-2008, 03:22 PM

Quote:

Originally Posted by Hatterasguy

Guys read the post he did that. Also Merc's have a pump in the drive like an outboard. I have actualy never done one because I have always had Volvo drives. Volvo's only have a pump on the engine.

Impellers last 4-5 years, unless you run them dry or in silt.

What HAT said.
If it runs fine on the hose, but gets hot at idle, it must be a low speed flow issue. Did somebody replace the engine water pump with an automotive one?

If so, probably not a stainless or bronze impeller, and has rusted away.