454 overheats under load

[jobie]

I AM ABOUT TO LOSE MY MIND !!!! 88 25' sea ray 92 or newer mark v block ( i looked up the numbers on the block and thats what i came up with ) with thunderbolt ignition,fresh water cooled ,bravo II drive. i bought this boat at an estate auction and have no history on the boat or when it was repowered. the boat overheated on the muffs in the driveway. i pulled the raw water pump and the impellar was in a bizllion pieces !!! i put in a new impellar and back on the muffs the temp never rose above 160 degrees. i did back flush the power steering / oil cooler and the heat exchanger !!! i launched the boat and above 2000 rpm the temp rapidly climbed to 220 , dropped the throttle back to neutral and the temp dropped back down to normal . i can run the boat all day at just under 2000 rpm and it will stay cool. as i said i know no history so i tore it apart and replaced the thermostat , coolant circulation pump . i pulled the risers and although they did not look bad i soaked them in muriatic acid and they came out clean as a whistle. the boat did not have an expantion tank on it so i installed one however it does not appear to be transferring coolant back and forth but coolant is bubbling over and being pushed out the cap when it gets hot . could the cap be an issue ? oh ya and it still overheats !!!! i considered the fact that i might have a bad head gasket but there is no water in the oil , my plugs look brand new and there is no excessive exhaust smoke when she is on land . i pulled the line coming from the raw water pump to the heat exchanger and ran the motor i had what appeared to be good flow and it appeard to increase as i throttled it up !!! i have been told that the line coming through my intermediate housing might be pinched ??? the boat has a mascerator and tommorow i am going to attach the raw water intake hose to the seacock thru hull fitting for the mascerator and run it that way and see if that changes anything. anybody got any other thoughts ???? this is my first fwc cooled boat , the local marine mechanic recommended using dex-cool 50/50 coolant so that is what i have been running it on.

 

[Bifflefan]

Re: 454 overheats under load

Head gasket is a good guess. you dont have to have water in the oil for it to be a head gasket. The pressure from the cylinder gets into the cooling system and just pushes the water out of the way.
Id get teh engine warm on the muffs. then pull the plugs and crank it with the water running throught it and see if water coming out a plug hole. This wont rule out a head gasket, but it will tell you it is a bad head gasket.

 

[seattle2855]

Re: 454 overheats under load

How much water flow did you have to the heat exchange? I had what appeared to be "good flow" too but still had overheat issues under load. I believe you should be able to hold the water line vertical and the water should come out 2 - 4 inches high. Any less isn't enough.

Also, what did your impeller housing look like? I had a good impeller but the housing was bad.

 

[jobie]

Re: 454 overheats under load

as i stated this is my first fwc boat. this was the first raw water (engine mounted ) impellar that i replaced and the housing looked fine to me. after i assembled it it was just about impossible to turn with my bare hands , i was told thats the way it should be !!! as far as water flow i would say that the water only comes up out of the hose 1-2 inches . any thought on my expansion tank why the coolant isnt being drawn from there ?

 

[cr2k]

Re: 454 overheats under load

Back flushing the heat exchanger is not always enough. Ends of the impeller blades will lodge in the tubes length wise and may not always be visible. You may need to remove the heat exchanger and "rod it out" to make sure all the tubes are clear.

 

[jobie]

Re: 454 overheats under load

forgot to add that , i opened up heat exchanger and rodded it out this afternoon. at each end there was alot of what appeared to be zinc material ????

 

[Maclin]

Re: 454 overheats under load

Blown head gaskets do not always put water into the oil, so that is not a good deductive tool. Best way to check for head gasket leak is a compression test, then if one or more are low do a leakdown test on them.

 

[jobie]

Re: 454 overheats under load

i didnt think to check my risers when the motor is hot. i got up early this a.m. went down and went for a ride at the dock 160 degrees my risers are not even warm to the touch !!! when the motor heats up i cant place my hands on them for 5 seconds. now i am thinking that my raw water pump needs to be replaced. i pulled the line again and the water is only coming up 1-2 inches

 

[Don S]

Re: 454 overheats under load

i pulled the line again and the water is only coming up 1-2 inches

Which line are you talking about?

 

[jobie]

Re: 454 overheats under load

sorry , the line coming from the raw water pump where it connects to the heat exchanger.

 

[Don S]

Re: 454 overheats under load

So you disconnected it AT the heat exchanger??????
Is your heat exchanger on the back of the engine? Have you checked the transmission and oil coolers to make sure they aren't plugged up?

 

[jobie]

Re: 454 overheats under load

boat is an i/o setup( bravo II ). the exchanger is mounted to the front of the engine. i did back flush the oil cooler, when i did it i zip tied a sock to the inlet end of the hose figuring that if there was any debris in the cooler it would catch it. after a few minutes i removed the sock and there was nothing in it. i continued to backflush for a few minutes and had a had steady solid stream of water .

 

[jobie]

Re: 454 overheats under load

went down to the boat today ( it is in the water ), i attempted to hook up my intake hose to my thru hull seacock ( for the mascerator, couldnt be done , i would have to remove the pump in order to get enough hose to relocate it. anyhow when i pulled the water hose ( going to the raw water pump ) from the transom assy inside the bildge i expected water to come flowing in however it was only trickling in. is it possible to have a blockage somewhere beyond that point. again i bought this boat with no history. there is a piece of the skeg broken off. is it possible that the boat was pulled out of the water with the drive down and the drive got driven all the way up and damaged something in the drive that is know creating a blockage ?

 

[jobie]

Re: 454 overheats under load

oops i forgot to mention , i figured if i took a hose and sprayed it into the fitting that the line attaches to the water would flow through and i would see some bubbling out the back of the boat. no bubbles and the water did not flow through well . as a matter of fact when i put the hose up against it the water was spreaying back at me as it would if you pointed a hose a a wall !!!

 

[Maclin]

Re: 454 overheats under load

I may be wrong but I think your setup has the raw water pump on the engine. This means the water stream coming into the raw water pump from the external hose would have to be able to get by the non-moving impeller in order for it to continue out the exhaust, pretty sure that will not happen.

 

[Maclin]

Re: 454 overheats under load

I just read your new thread, I may not have understood which way you are trying to put the water through.

 

[jobie]

Re: 454 overheats under load

hi maclin , thanks for your interest and following my threads !!! it has a bravo II drive which does not have a pump in it , you are right the raw water pump is engine mounted. inside the bildge , behind the motor the raw water intake line that goes to the raw water pump attached to a fitting that draws water up through the drive. that is the line that i am talking about.

 

[jobie]

Re: 454 overheats under load

if my risers are getting hot to the point that i cannot place my hands on them wouldnt that rule out a head gasket ???? even if i had a bad head gasket my risers should not get that hot if i had good flow to them. is that right or wrong ???

 

[Haut Medoc]

Re: 454 overheats under load

I have not heard any mention of checking the thermostat.....
There is a simple chemical test available to check the coolant for the presence of exhaust gasses at your local auto shop....
Lack thereof will rule out a bad head gasket....
I doubt it is a head gasket......
The fact that your risers are hot suggests a raw water flow problem....
If your heat exchanger is 20 years old & has been in salt water for most of the time, I would take it to a radiator shop & have it boiled & rodded.....

 

[1980Galaxy]

Re: 454 overheats under load

he said in his first post that he replaced the t-stat.