2003 crusader 8.1ho overflowing coolant bottle, engine does not overheat.

Hello all. Great site with great info.

I have a 2003 crusader 8.1ho engine with 600 hours on it. Boat has only been in fresh water. I recently noticed the overflow bottle was completely full and coolant was spilled all over the place since the overflow bottle overflowed. I took off the heat exchanger cap and noticed the coolant was low as the coolant did not return to the heat exchanger as the engine was cooling. I returned the levels to normal. I ordered two new radiator caps. I tested the old cap and found it was fine. I still went ahead and replaced the cap. The boat runs fine around 2000rpm at that rpm the bottle will not overflow. But if I run the boat at cruise around 3600 rpm the overflow bottle starts filling and eventually overflows. I have also pressure tested the engine cold and found no leaks. The engine will hold pressure. I called crusader and they think the system is sucking air somewhere and that is driving the coolant out of the heat exchanger. I have looked down into the overflow bottle while it is filling and do not see bubbles. I have tightened all the hose clamps. I have checked the strength of the antifreeze and it seems to be at the correct 50/50 strength. Which is -30 degrees. The strength out of the gallon jug of prestone 50/50 antifreeze is -34. Oh and the engine does not overheat. I have a digital temp guage on a b and g engine and it reads about 160 at 2000rpm and 166 at 3600rpm.

i am out of ideas and am hoping someone has some ideas. Thank you in advance for your answers.

I would guess (guess being the word here) that the fluid must be forced out by the incursion of another liquid or of a gas. Another liquid would be raw water and that seems unlikely, because the system, at temperature, is under pressure and because you do not see dilution of the coolant. Gases would include sucking in air, boiling water, or combustion gas.

I don't like the sucking air theory because it only happens at higher rpm and the coolant system holds pressure cold.

Localized overheating producing boiling could do it, however in my experience (it happened to me, weird overheating is almost a hobby) once the steam gas bubble exiting the head got to the temp sensor, the temps immediately soared to a big time overheat. Also because the gas does not last (condenses back to water), most of the coolant expelled get sucked back in.

Combustion gas getting into the coolant system and displacing fluid could be explained by a head gasket leak or crack that only opens in times of higher stress (3600 rpm) and produces a one way flow of gas into the coolant. Unlikely but certainly not impossible. If that is the case you could detect it by testing for combustion gas in the coolant (tester available at Napa). If positive, you could likely find where the leak is is by doing a leak down test with compressed air on each cylinder. Then you would have to pull the head on that side and see what's up.

Good luck (and you may get some much better guesses!)

CaboJohn

The "sucking air" comment could have been directed at the raw water side of the cooling system. any idea when the raw water pump was last serviced?

Sounds like you have a cooling system pressure tester so you can do the combustion leak test with it and then use the test strip as verification...that said, its not the easiest (or most accurate) test to perform. if yours is a twin engine istallation, you can use the "good" engine to provide a point of reference.

BTW, there are many other measurements to "test the strength" of a coolant; freezing point is one. And 100% water in the closed side will transfer heat more efficiently than coolant.

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Cabojohn thank you for your reply.

makomark the impeller in the raw water pump was replaced last year this is its second year. It gets replaced every other year.

Had the mechanic out he started by pressure testing the cooling system. He got the same result i got the system held pressure like it should. he also preformed a compression test the largest difference between cylinders was 175 and 160. He did notice that as he was revving the engine up to 2000rpm as he was releasing the throttle and the engine was returning to idle the heat exchanges cap was leaking some coolant. I don't believe this is my issue but I did remove the heat exchanger and take it to a radiator shop to have a new neck soldered on. While it was there I told them to make sure there are no leaks between the coolant side and raw water side. I believe this issue was created by the constant removing of the cap. The neck seems the be very fragile and easy distorted. I originally had trouble making the tester seal to the neck and after comparing it to the good engine the bad engine seemed to have some high spots on the neck after tapping those high spots down I was able to get a good pressure test. But it seems like those high spots return after the cap is installed and removed.

the mechanic sniffed the exhaust and could not detect any sweet smell from coolant.

Even will the heat exchanger a little low on coolant and the overflow bottle empty the overflow bottle rose to 3/4 full in the slip with no load on the engine and occasional revving to 2000 rpm. The engine ran about 20 min during that test. My point is that If the coolant was at the proper level when the test was started it would have certainly overflowed out of the overflow bottle.

Thank you everyone for your responses.
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Hi Crag,

You have some more data but don't have a cause or solution yet. I gave you my "good" ideas in my first post and I will stick with them. Based upon your difficulties with the cap and seat I would now vote for an incompletely filled system (air bubble) and an overflow/return system that is not working properly (or one that since your possible fix has not had the opportunity to work properly). Air bubbles make strange things happen. A bubble could be lodging in different places in the block based on rpm. When you change rpm the bubble moves and the coolant exposed to the very hot area where the bubble used to be instantly boils, over pressures the system and expels fluid.

Back in the day when I chased an overheat problem I looked up the expansion ratios of water and glycol and calculated the amount of fluid that would be expelled into the overflow tank on a Crusader 350 if the engine was full and went from 80F to something like 215F. As I recall it was a little less than half an overflow tank. So if your math is similar, and you are overflowing (or expelling when you backed off from 2000 rpm) that is not right.

Since you really do not want it to be an expensive leak of combustion gas into the coolant (it still could be, head gasket leaks can be one way because of the high pressure of the combustion gas so your mechanics sniff test is useful but not definitive) and since Mark did not explain exactly how to do a combustion gas test on a marine engine (I was hoping he would, since I always seem to mess it up......although I did have someone say to just do it in the overflow tank and that would work. Maybe.), I would try the following:

Assume the leaky fill cap seat was good news and the bubble theory is correct until proven otherwise and work to get rid of the bubble. You need to get enough fluid into the system (squeeze hoses, rev cold engine very briefly, stop and add fluid, try running at idle with cap off and add fluid, etc.). Lots of tricks and some of them work some of the time. Others may suggest their favorites, some of which also work some of the time. The point is that you must get enough liquid in that you can check if the coolant return system works. Too much air and your coolant could expand without increasing the system pressure enough to open the relief in the cap and start to force out the air. Once you have all the fluid in you can get, you must start with a cold engine, bring it to temperature and shut it down. At least three times, maybe more. Even the first time should suck some fluid back when the engine cools, even if it only expelled air. If you do a very good job of filling (let's say a bubble smaller than an orange), and if the system is working usually your first voyage is OK, although I like to do one heat up at the dock just to see how much fluid get sucked back in (overnight).

If the system works, then the cap is sealing, and hopefully all will be well after some heat/cool cycles. Since you good be fooling around a lot trying to get out the air you might try putting a cheap (usually less than $10) 0-15 pressure gauge into the coolant overheat port on the intake manifold. That will make it clear if you are getting the system up to cap pressure (likely 7 psi) and if you are bored you can watch the pressure go back to zero and the sucking begin.

I have repaired one Crusader coolant cap seat and replaced another. They are very soft. Both bad when I got them. Secret to long life seems to be a gentle hand. Look, don't feel, to line up the cap to to the slots. Push down steadily with the heel of your hand and then rotate smoothly all the way to the seal position.

Good luck,

CaboJohn

UpDate

Starboard engine is now fixed. While I had the heat exchanger out for repair I decided to replace the thermostat for the heck of if as it was part of the heat exchanger assembly and the system was already drained. After refilling the system and purging it of air. I have retested the engine several times and it appears the issue is gone. In my opinion the heat exchanger cap issue was caused from all the testing and messing around with the cap. It was the thermostat that was causing the issue. The mechanic talked to crusader and after he looks a at the thermostat diagram as he had some questions. It seems that the thermostat was not opening fully and causing excess pressure to build which was forced in the overflow tank. However the engine did not overheat. What ever the cause I'm glad it was cheap and the engine did not have any major issues. Thank you for everyone's help. I plan on replacing the neck and thermostat on the other engine. As I'm due for coolant replacement and might as well service that engine while the coolant is drained. See attached diagram of thermostat operation.

I am glad you found it and it did not cost an arm and a leg. Crusader uses several "bypass" schemes, depending upon the year and model. Engines need some way to circulate some coolant to the block even when the thermostat is closed. In my case (I am assuming here that my boat survived the recent hurricane in Cabo) one engine uses three extra holes in the thermostat, so it never closes all the way. The other engine does not have the holes, but uses the path though the water heater (just as a car engine uses the heater core) to provide the bypass.

Both those approaches are pretty much failure proof. In your case (same year, bigger block) Crusader opted for a more complicated approach with a special thermostat. Don't know why, but there must be some advantages. My Kohler generator also uses this type of thermostat to open and close the bypass, only smaller.

CaboJohn