Thermostat Replacement

My 385HP 8.1L Crusader engine

My 385HP 8.1L Crusader engine is overheating. I suspect that the thermostat needs to be replaced. The boat is in a remote location and is difficult to get someone to come to the boat and service. Is replacing the thermostat an easy task. I am told the the system needs to be purged. Any tips or procedures on how to do this would be appreciated.

"Ted, welcome to what I consid

"Ted, welcome to what I consider to be the best forum on the internet. If you want to have beneficial discussions with people experienced in maintenance of Crusaider engines (both professional and long time amatures) this is the place to be.

The subject of overheating engines is a frequent topic of discussion for this forum. First I would suggest you make a search of past messages concerning this topic. It will give you a good understanding of the different issues that may be working individually or together to cause an over heating problem.

Usually a little more information is needed in order to get the conversation going. Things like:
1) Is your engine fresh water cooled or raw water cooled?
2) Is your boat in fresh water or salt water?
3) How long has it been since you did any maintenance on the cooling system?
4) What is the temperature of each engine exhaust?
5) Do you have access to an infar red gun for making some measurements?

I think you will find that upon reading the various threads on this forum concerning this topic that although a stuck thermostat may cause this problem, there are probably other more likely culprits.

Again, welcome and have fun.

Chuck Hanson"

Chuck.

1.)I have a raw

Chuck.

1.)I have a raw water loop and a loop with coolant.
2.)The boat is used in saltwater
3.)New risers in 08. Coolent replaced
4.)This past weekend temp runs 200 degrees and rising with use. On previouse outing engine temp had fluctuated 10-20 degrees so I have been keeping a close eye on it.
5.)I'm checking on it. Where should I take measurements?

The raw water loop is pumping water.
The crank sensor was replaced this summer because engine would not start when warm.

I will search database tonight.

Thanks
Ted

"Ted:

Chuck got you off to

"Ted:

Chuck got you off to a great start; here's some specifics on your issue.

The hardest part is gonna be finding the thermostat. the 8.1 system has all the traditional parts; their locations are unconventional. the thermostat lives in its own housing. Couple variations based on year. Nothing special about the service aspects. All systems with fresh water cooling (FWC, which is what you described) require purging the coolant side.

Best way I've found to purge is to mix up the coolant at the correct ratio and pour that into the system. Start engine and top off coolant. Run engine at fast idle until the gauge starts to rise. As soon as the thermostat opens, reduce the idle. watch the reservoir - the coolant level should drop as soon as the thermostat opens. let it cool down and add coolant to the correct level. You may have to repeat a couple times to purge all the air.

May want to check out the parts list available on the crusader www site.

I'd be inclined to think your issue is on the raw water side vs the thermostat. you need to make sure you have sufficient water flow there or it won't be able to cool the fresh water loop. A stainer cap air leak or a partially open sea cock will cause overheating, too."

"Chuck,

Did you just buy th

"Chuck,

Did you just buy this site? What a great post. I guess if a boat is new or old, it would still have headaches to deal with!

And I absolutley agree with you !!!! Great place and people."

"did you pull the raw water pu

"did you pull the raw water pump and yank the imepller?? Easy fix and its only 30 bucks, and heck it never hurts to get a new one!!"

The engine is 2004 model and I

The engine is 2004 model and I had the impeller replaced this past spring. The strainer is clean and cap is tight with no evidence of leaking. I was diving under the boat to check for excessive barnicles on the strainer on the hull. It was in pretty good shape for this time of year. I will double check all conditions next time I'm on the boat since the engine has now cooled. In the meantime if anyone has any thoughts please forward. Thanks for all the help.

"Ted,
Did the temperature ris

"Ted,
Did the temperature rise suddently? Or was it a gradual rise over time. Most times a sudden fluctuation or rise in temp could be caused by a failing thermostat (if all else is normal per say and you have not boated in new area full of seaweed or something). Gradual increases over time are usually caused by low flow in the cooling system (i.e. bad raw water pump impeller, clogged exchangers/U-cooler/strainer/risers/elbows, etc.)"