[Gina Bella]

This is my first season as a Tiara 3100 open owner. Is it normal for the coolant to appear low (not topped off) in the cylinder shaped tank and filled to the top or overflowing into the overflow jug when the engine is warm? Is there a technical or proper way to top off tank?
Thanks in advance.

[ReelMagic]

As a prior owner of a 31 Open (1997) w/twin 454 FI Crusaders I can provide some info regarding the cooling system. The cylinder on the top of the engine you described is the "heat exchanger".. That transfers the heat from the engine antifreeze to salt water (or fresh water based on where the boat is kept) via cooling rods internal to the "heat exchanger"... The overflow tank allows antifreeze from the "heat exchanger" to expand into the tank as the antifreeze gets hot during engine operation keeping the system at or around 14 PSI (could be 7 PSI based on the pressure cap used).  The overflow tank has 2 marks, one shows where the antifreeze should be when the engine is cool and the other mark is where the antifreeze should be when the engine is hot.... When you first shut off the engine (and the engine is hot) the overflow tank level should be near or at the high level. Once the engine cools off the level should return to the cool mark. As the engine cools down the pressure in the cooling system goes down thus sucking the antifreeze back into the "heat exchanger".... Once the engine is fully cooled the "heat exchanger" should be full or nearly full if checked..... The way you should be filling the system is through the overflow tank..... When cool you can add to antifreeze through the cap on the heat exchanger till full although I recommend keeping an eye on the level in the overflow tank. When cool ensure the antifreeze is no lower than the cool level... Hope this helps....... 

[rose_surfer]

the answer above is an excellent explanation and is consistent with the way most freshwater cooled engines like yours work. To get the root of your question though, it doesn't sound normal to me to have your heat exchanger low on coolant. It's hard to tell how serious without knowing how low. But I'd start with topping it off and then checking again after some run time. Also keep an eye out in the bilge for any coolant. Also, if I'm not mistaken, on my 454s, theres a little sticker saying to top off the coolant at a certain rpm - 1200 or something like that. I guess the idea is for the engine to be circulating but not hot. You might check your engine for the same, or look it up on line. My engines are 1989 crusader CID. Finally, if you ever get (or suspect you have) air in your system (usually from breaking into it - checking a thermostat or something like that), you bleed the system by removing the plug at the top of the thermostat housing with the coolant full until coolant spews out. Just a few more tips on the system...

[sbw1]

One cause of low coolant is air in the system after it has been drained and refilled. We have 8.1 Crusaders and the set up on our boat sounds very similar to yours. The owners manual talks about the importance of changing the antifreeze when the pH reaches a certain specified level that indicates it is time to change the coolant. On our boat it lasts about 4 years. I've noticed that the fluid levels on the overflow tanks will be about midway between the add level and the full level after the tech does the work. The first time we run the boat after the change, the levels will drop, some times below the add level. Both sides will be different. When the boat cools down, I add antifreeze to each side as needed to bring the levels up to the mid points again. I may have to do this 2 times and sometimes three before levels stay constant. Once equilibrium is reached levels stay the same for the four or more years between changing the fluids again. Levels should stay the same or your have a leak somewhere. Also, it is critical that you add antifreeze that is compatible with the engine spec and do not mix types. Mixing will ruin your engines.

[justrollin]

Several times a year the fluid should be checked for proper level and checked for strength for freeze zone most important if you live northeast where antifreeze can freeze and crack engine parts when temps hit below 32 deg.

[Uhehner]

I think all of the above information is correct. I might add that the heat ex-changer cap must seal to the tank.  It must not be a vented cap. The cap should have an 8- 15 lb pressure rating and bleed excess coolant to the overflow tank via a hose from the top of the HE tank to the bottom of the OF tank when the engine is hot and the coolant expands.  The heat ex-changer tanks on all my Crusader engines were always full to the top when I removed the cap when cold. The coolant level in the over flow expansion tank goes up and down depending on engine temperature. You never need to remove the heat ex-changer cap, just add coolant to the overflow tank as needed. The overflow tank cap is vented and does not seal to the plastic tank.  If the coolant level is always low in the HE when cold, I suspect you have a bad pressure cap.  Capt.  George