5.0 FWC Merc losing coolant-HELP

FlyingBlind310

So my port engine is having a problem keeping all of its anti-freeze. A few weeks back, I found the heat exchanger low so I topped off and asked my mechanic to take a look-apparently the gasket at the t-stat housing was leaking. "Fixed" says the mechanic; however, last weekend I got the boat and the heat exchanger was low/empty. After a "friendly" conversation at the yard (PO-ed I needed to cancel Labor Day plans), the owner of the marina came down and pressure checked the system...held 15 PSI cold and maintained 15 PSI with the engine running at operating temp...no visible leaks or signs in the bilge. Now we are both stumped. Here are some additional facts:

- engine runs fine when started/at idle/at cruising speed; however needs full throttle in order to start (new coil/IAC. possible bad fuel regulator?)

- Engine temp will spike to 180+ under way and then come back down to 160 when at the dock at idle for 10 min

- raw water impellor replaced last year with under 30 hours on it

- heat exchanger just sent to a radiator shop and showed a leak at 22PSI (isn't this above operating specs?)

Any ideas on where else to look for this leak? Could this be the start of a blown head gasket (coupled with the hard start)? Appreciate any ideas/suggestions before I turn the mechanic loose.

Black_Diamond

Are you sure it is leaking and not purging due to high temp?  Are you fuel injected?

FlyingBlind310

EFI..where would it purge? out of the cap? No evidence of that.

Black_Diamond

If it's not bleeding out from the cap (over pressure ie overheat) then it is either going into your raw water, it would almost have to be a leak in the heat exchanger or a bad head gasket, assuming you don't have it in your oil.  The head gasket might explain the hard starting issue too.  You should not have to have the throttle wide open with EFI to start as you know. 

212rowboat

Dye it, and light it up... for your hard start, remove and either clean or replace your IAC, and clean your throttle body... check your circulation pump weep hole... with no fan on the shaft, it's hard to tell when it goes bad... It may not be pumping sufficiently at speed... Make sure your IAC is an oe device, not some cheap aftermarket... 

FlyingBlind310

IAC was just replaced w/ OEM. What dye would I used for the coolant system?

BD-no water in the oil...I've been monitoring that closely. It needs about 5-10 seconds at full throttle to final turn over...def not SOP for an EFI

212rowboat

Was the passage the IAC mounts into.cleaned with throttle body cleaner?  If it was dirty (and they all get filthy) it was just kicking the can down the road... but.. cranking that long speaks of spark and not air... A pcm will limit spark until all sensors report... I'd pull every sensors connection and blow it out with contact cleaner, add a sheen of dielectric grease, and plug them back up... There is no telling short of a scanner tool which sensor is slow on reporting, but any of the major ones can cause the pcm to limit spark... it could be your tps, your temp, your IAC, your cps, your ckps, or your map... If it's catalyzed, it could be an o2... If you were to have mentioned it's catalyzed, that's the very first one I would have suggested... They do strange things when they go bad. 

The dye is made for cooling systems... It reacts and glows under UV light. it makes it real easy to find leaks... one thing about phantom leaks: they often leak only at a specific temperature range, which makes pressure testing tricky and finding it difficult... first thing I'd do is place a piece of tape over the weep hole and run the engine a few minutes, then pull it to see of there is a drip or if its wet... 

By the way, coolant on an o2 sensor is a death sentence for them... They don't like that at all... This combines your issues, too... Coolant burns white... Can you pull your boat and run it on muffs so you can see the exhaust plainly?  

FlyingBlind310

Well less than a year later...I had cracked heads on both cylinder banks...slight cracks which caused the engine to operate and not lose power, but tough to start warm.

Had the heads replaced last month and running fine despite the lighter wallet. My mechanic said he had a tough time finding 5.0 heads as they no longer manufacture...any truth to that?

Michael T

Did you figure-out why your heads were cracked. I can see that your boat is 14 years old but why the cracked heads - a bad winterizing job, overheating? Just interested.

FlyingBlind310

I think it was a problem that I inherited with the boat...I think the previous owner used K-seal or some other sealant in the FWC system as a quick "fix" to something as there was some muck in the coolant. Last summer, after a few months of owning the boat, I noticed the hard starting and started replacing parts left/right. I also had a leak in my heat exchanger. Would the heads go in a FWC motor? I would think the anti-freeze would prevent that at least in the block/heads

I think the bugs are out - keeping coolant and starting well.

Michael T

Fingers crossed FB!