Intermittent Overheat at start up...

[Pete Bruzik]

Hello All,
Universal M35B
I have an unusual issue - intermittent overheating...
current engine hours 2,250 (C350 - 2003 #107)
Heat exchanger was cleaned out etc in 2014 (no problems prior - just slightly higher than normal temps - had removed / cleaned as solution)
Anti freeze (50/50) checked prior to every start
Lets start with the symptoms - at start up (sometimes - not always) no raw water flow from exhaust
Replaced impeller - old one did not have missing vanes - I replace every year at start of season - 2015 replaced twice - but probably did not need to replace second one but did since I had overheat issue. Sea chest clean, hoses OK all are relatively new
Still had this "sometime" issue at start up - and I have noticed that temps rose battling significant seas on the bow which is not normal for us.
All this happened on our aborted trip to Florida / Bahamas this past fall - we got as far as Charleston SC when family emergency forced return
No leaks of oil or water from pump - the pump is still the original!!
When I start I have found that if there is not any water exiting the exhaust pipe if i increase the RPM's and slow back down while in idle then the water flow comes back sometimes after first try sometimes multiples) I do not have a the water flow issue at start every time - just sometimes.
I do not have any hoses leaking - I have checked for air bubbles in both raw and coolant side after replacing impeller.
Should I just replace the water pump?
Any ideas out there??
THANKS,
Pete Bruzik - PEKABU 3 - original owner of #107

[william vanwagoner]

I would check the seawater strainer and raw water seacock. There may be some debris which intermittently blocks the flow of water, possibly creating a complete seal and blockage when the flow increases on initial throttle up. I know of a case where a small fish was stuck in the seacock and moved up due to suction when the engine was turned on blocking the flow of water into the seawater strainer.

[Pete Bruzik]

Hi Bill - checked thru hull at the same time I was checking sea chest - we always shut the thru hull when we leave the boat.
On the trip back north ran the generator along with the engine all day on the next to last day of the trip it was a very COLD day - heat was wonderful - since the thru hull is large and calculated flow was more than sufficient for teeing off to supply the generator as well from the engine thru hull - I have run both many times during the summer months for AC with out an issue.
removed the hose from thru hull just to check - nothing blocking...
This is a strange issue - if I need a new pump fine - but hate to do that if I really dont need to.

[knitchie]

Another suspect is an airlock in your cooling system. A friend had an airlock in his fresh water loop that caused overheating. We had to be bleed it out. This may not explain why the raw water loop is not flowing freely, but you might want to check by breaking each connection in the flow circuit to see how far the water is flowing. You may find a blockage anywhere along the path.
Best luck,
Ken

[R.B.]

Work through your system to see where the water is not running. Disconnect hoses to make sure you have flow through at each section (eg. with engine off, disconnect hose from water pump output, start engine to see if water is being pushed out) I had to do this once underway, overheat situation, thinking it was a broken impeller pulled it out to check looked fine. Had to pull hoses to see where water stopped flowing. Turned out it was the pump. Pulled the impeller again, upon closer inspection, the impeller shaft (metal) was disconnected from the rubber, so it was spinning freely, but no visible damage.
Is it possible that your impeller is not engaged in the pump and not spinning while the engine is running? Maybe a worn shaft?

[Pete Bruzik]

Hi Ralph,
Interesting comment re shaft - makes sense - I will get a new pump and have it ready to replace as soon as the tarp is off!
Will post a follow-up and let all know if that solves the issue
Thanks to all!

[R.B.]

Pete just to be clear, in my case it wasn't the pump itself, but the impeller. The metal in the impeller that connects to the shaft was spinning without turning the rubber vanes. However since you have replaced yours several times, it may warrant looking more closely at your pump and it's connection to the engine. I would definitely diagnose more before buying a new water pump. I hear they are around $500. If you are interested and need a new pump, you can buy an Oberdorfer pump for half the amount. Slight modifications required to make it fit, but it makes impeller replacement much easier.

http://www.c34.org/wiki/index.php?title ... Oberdorfer

[Triumph]

Have your exhaust elbow checked if you have never replaced it. At this many hours, you would be do for it and it could definetly be causing the symptom you describe.

Bill on Triumph

[Pete Bruzik]

Hi Bill,
re exhaust elbow - wouldn't there be exhaust and or water evident inside the boat? if no exhaust or water evident inside the boat the exhaust elbow should be OK? What would you be looking for as far as symptoms for bad exhaust elbow?
Thanks - Keep the ideas coming - appreciate it!

[wolfe10]

Hi Bill,
re exhaust elbow - wouldn't there be exhaust and or water evident inside the boat? if no exhaust or water evident inside the boat the exhaust elbow should be OK? What would you be looking for as far as symptoms for bad exhaust elbow?
Thanks - Keep the ideas coming - appreciate it!

No. Actually, minerals can build up in the exhaust elbow and restrict water flow. Remove the raw water hose from the exhaust elbow and verify that there is no restriction.

Brett
2004 350 #180