Can you post details about your boat? Year, hull number, exactly which engine you have. The cause could be varied and without more details on what you have it's hard to do more than guess. Put this info in your profile and it will be automatically added each time you post.

I am with Bud, we need more info on you boat year.

Understand that unless added none of our boats had a raw water temp sensor. If you had the fresh water side open at any time it could be that you have trapped air in the top of the system where the temp sensor lives in the thermostat housing, the earlier boats have a bleeder at that location.
Even if you do have air in the system, it would be unlikely that the alarm would trigger after start with a cold engine, are you sure it is not your oil pressure alarm going off. If that switch were sticking it may take longer than normal to silence.

I installed a water overtemp probe on my engine as the original system did not have working a temp alarm, I was surprised to find that the temp alarm probe was adjustable, I installed it and it went off imediatly (I was alarmed), unlike the standard temp probe, the teminal screw depth sets the alarm point so I needed to stack washers under the screw after adjusting it. The probe was likely set when recieved but, the terminal is obvoulsly made for a clip in type terminal and I used a ring terminal under the screw and hence SCREWED UP the adjustment when I removed this screw.

Lazarski,
I am in agreement with Steve on this one. I've never heard of a high temp alarm going off with a cold engine. It's possible that the wires to your high temp light and your oil pressure light are reversed. They both feed the same alarm module. High temp is generally a solid tone, and low oil is a pulsating tone. When you first turn on the key, without starting the engine, you should hear the low oil (pulsating) alarm. Soon after the engine starts (3-4-5 seconds?), the alarm should go quiet. You should never (hopefully) hear the high temp alarm. If you do, the most likely culprit is a clogged raw water inlet or strainer. Your symptoms are strange.

Tom,

On this same subject, my oil pressure light goes on for a few seconds when the engine is started along with the alarm. However, the alarm is a steady whine that also goes off. I overheated the engine once (weeds in the intake) and there was no warning while the temperature gauge was maxed out and I had steam coming out of the exhaust. Fortunately I caught it quickly. What do you think is the probable cause?

Tom,

On my boat a 1988 MKI, there was no overtemp alarm that I am aware of.
I upgraded to the newer panel, including a new temp gauge, on mine there is no differnce in audible signals as the temp and oil presure warning share the same horn. My engine only had a temp sender with no provisions for a temp warning. I installed a temp warning switch on the engine and wired it to the warning horn on the panel paralel with the oil pressure warning lead. This horn has power going to it at the panel and the warning switchs give it a ground when oil pressure is low or the water temp is high.

It would be normal for the oil presure warning to go off momentarily on start until oil pressure builds up and opens the switch.

There's probably differences among the various panels, but on our vintage boat the warning buzzer has two tones. The oil pressure is on the intermittent and the high water temp is on a constant tone. There are 3 terminals on it, one a common and the other two are marked S and P (IIRC). Can't remember what those letters stand for but one is the intermittent and the other the constant.

I got a new alarm from the panel manufacturer as the one in there was pretty feeble and only worked intermittently. Now when I put the key on I get a really loud BEEP-BEEP-BEEP-BEEP (continue ad nauseum) until I start the engine and the pressure comes up.

Bud,
You are 100% correct when you say there are differences between boats. CY and their panel supplier, Seaward Products, have always changed/upgraded panels and features thru the years. On my 1975 C30, I don't think there were any alarms at all. At that time Seaward had an "upgrade" available which was a small circuit board that screwed on to two or three terminals of one of the gauges to turn an analog signal from the sender into a digital output for an alarm. Quite ingenious, actually. Other than salt and pepper, I think S and P stand for steady and pulsing (or pulsating?). If anyone is unsure of what their panel does or should do, they should unscrew it, and study the back. Look at the wiring. Take a few pictures of the front and back. Find the ID number (it's on a white paper sticker on the back of the panel, if it hasn't worn off). Try to figure out what your boat has, and what you want it to have. With that in mind, give a call to Seaward Products in CA. Dennis is THE panel guy there. He most likely personally built most of the panels in our boats. On Julandra (1987 boat) I upgraded the panel to a newer style, with the two-tone alarm. It entailed drilling and tapping the housing for the thermostat on the engine for a second temp sender, but I ended up with a temp gauge, temp alarm, and oil pressure alarm. I believe most MkIIs have that setup, but I'm not sure. Your boat, your choice.

Tom,

I had purchased the overtemp warning switch for my engine and it sat in one of my drawers below the chart table for some months as I was not eager to drill and tap the thermostat housing and risk getting shavings in the housing.

I then looked at the bleeder screw on top of this housing and found it to be the same thread size as the switch. I removed the bleeder and ran in the switch, piece of cake. Now in the unlikely event that I need to bleed the air out of the cooling system I can just back the switch out until I get water at that location.

Steve,
That's a GREAT idea! Removing the housing is fairly easy to do, and being cast aluminum, is very easy to drill and tap.

Tom,did you purchase the over temp alarm from Seaward?(the one that screws into the thermostat housing)..maybe this is something that i can buy locally.

Greig,
I did it a long time ago, but I THINK I purchased the temp sender from a local Westerbeke/Universal dealer. Seaward assembles panels for our boats, but I don't think they sell any engine parts. I could be wrong. Seaward has been so helpful in the past, I'd suggest calling them first, and finding out exactly what would be required. They could probably give you the specs on what type of temp sender is required.

Steve, you can also do this, without taking your temp sender off, reply #6: [url]http://c34.org/bbs/index.php/topic,4518.0.html[/url]

[QUOTE=TomSoko;6228]Steve,
That's a GREAT idea! Removing the housing is fairly easy to do, and being cast aluminum, is very easy to drill and tap.[/QUOTE]

On my engine, the housing isn't thick enough to really tap it. What I'd have to do is weld a nut on the inside of it (not worth the hassle).