I am new to the club and was wondering if anyone has had this problem?
I have twin 7.4l mpi Crusader engines and one of them i running around 195 to 200 degrees. The coolant overflow bottle was blowing out some coolant so i tried to trouble shoot this without any luck. I changed the thermostat with a oem part, replaced the 7lb coolant cap, and nothing changed. I bought a IR temp gun and found that one exhaust manifold is getting hot (230 deg ) Shot the other one and only reaches 170 deg. The other engine manifolds are running also 170 deg on both sides. The Elbows ( All 4 ) are running at 120 deg., engine blocks about 150 deg, and both oil coolers are at 100 deg. Just that one Manifold is hot. I took both coolant lines off and ran a fresh water flush through and found no debris. tried to backwards flush and still nothing. seemed to have a pretty good flow of water but not so sure. I put it all back together and did a test run. Guess what, still running hot ! I could use some help if anyone has had this type of problem.
When was the last time that exhaust manifold was changed? Might be time for a new one. They are a routine maintenance item, especially if being run in salt water.
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Not sure, i just purchased her at the end of last season but there is no salt water running through the exhaust manifolds, Just anti-freeze
I had a problem with overheating as well. Same engines. My port side would overheat if run much over 3100 rpm.
I changed the elbows, which are salt water cooled. They were due and rusty. No improvement. Ran Barnacle Buster thru the salt water system and changed raw water pump impeller, no change. Pulled the oil cooler and heat exchanger and had a shop clean them. NO CHANGE!
One day while poking around it looked like the hoses that run from the thru hull fittings to the raw water strainers was starting to crack and as a matter of maintenance, I decided to change them. After pulling the port side hose off of the thru hull valve, I opened the valve briefly to see what kind of flow was there. It seamed weak so I stuck my finger in the valve and there was a giant barnacle inside the ball of the valve.
Problem solved. The other work needed to be done anyway, but check your raw water systems carefully. When was the last time the risers/elbows were changed? Rust can plug them up slowly. Your cooler and heat exchanger could have crud on the raw water side. How old is you raw water impeller? Hoses have been known to delaminate on the inside thus restricting flow.
Chasing these issues can be a pain, but if your fresh coolant is clean, the problem is on the raw water side 99% of the time.
Good luck and let us know what you find.
Thanks for the feedback Paul. I replaced the impella over the winter and have the same amount of flow out of the exhaust as the other engine. With that said, i can only find a hot temp in one place on the entire engine, the whole exhaust manifold on the starboard side of the port engine. Every where else i shoot the temp gun is cool. I ordered the two hoses that feed and return the coolant to that manifold, as i agree, they could be bad. i also ordered a new manifold and elbow with gaskets, block off plate, and bolts just in case. I had planned to replace all of the manifolds and elbows at the end of the season as a normal maintenance procedure. Just don't want to do all that in the water. Hopefully this works. Keep your fingers crossed for me.
When you changed the impeller what did the inside of the pump look like? Was there any scoring on the cover plate or the back wall of the pump? I had a similar problem and the issue was that I was getting water just not enough water. And the cause was the scoring on the inside of the pump did not allow enough vacuum pressure as there was "Blow by" due to the scoring in the pump.
Inside the pump was in good shape. The raw water has good flow and i think the whole engine would be getting hot if it didn't. only that one exhaust manifold is getting hot when i shoot it with the ir temp gun. i think the engine itself is getting up to 190 (so the gauge shows ) because of that one manifold reaching 230.
I would start at the raw water through hull fitting and check everything. Replace the intake hose, ensure there are no air leaks on the strainer, check for debris in the oil cooler restricting flow, etc. Bob
I know you are stuck on the fact that only one of the manifolds is getting hot therefore you are eliminating everything prior to that (oil cooler/waterpump/strainer/etc..). I would not do that. It can be any of those things and more. It can be there is just not enough water getting to that side of the motor because of a restriction somewhere down the line. Chasing raw water problems can be a real PIA but you have to start at the beginning.
06-24-2020, 04:15 PM
(This post was last modified: 06-24-2020, 04:17 PM by 0007Boating.)
I Agree, but this is antifreeze ( fresh water cooled ) Not raw water. The raw water system is cooling everything that it is supposed too, heat exchanger, oil cooler, and the exhaust elbows. ( at least i believe that's everything ) so the way i see the flow of antifreeze is starting at the heat exchanger then going to the thermostat that tees of to the engines water pump, and also off to both exhaust manifolds, then coming out of the manifolds and going right back to the heat exchanger. The big circle of cooling life ( Lol )
If I'm wrong, please help me understand