So I did some extensive searching on the forums before posting these questions but a lot of the info seemed to be conflicting. Sorry the post is so long, just wanted to give as much info as possible

I have a new to me boat with a pair of '99 502 MPI Mags with 480 hrs, raw water cooled with original manifolds, supposedly religously fresh water flushed after every use by the previous owner (but you know how that goes ). Here's the concerns / questions.

1) The water temp gauges show engine temps between 180 - 200 once warmed up both at idle and underway. I wasn't too concerned with that figuring that the EFI engines would be calibrated to run a bit warmer to stay out of cold start enrichment but on the other hand this was in 70 degree air temps and the water is still pretty cold here. May become a problem in 90 degree heat with warmer water? I put new t-stats in (purchased from the local Merc dealer) this spring and I beleive they where 180's which would jive with the engine temps but then I've read some say that these engines should have 160 thermostats and others say 180's. Which is it and if it's normally 180's can you get away with running 160's with the stock ECU calibration?

2) There is some pretty substantial steam coming from the exhaust. It is definately white steam and not oil smoke but there's a lot of it and it happens at idle, while running, and a whole bunch when coming off of plane. It isn't consistant while at idle (does it sometimes and not others), always after coming down off plane, and mostly only from the starboard engine while underway. Some say it is normal but my '06 Formula with 6.2's never has any steam to speak of so I'm not sure how normal this is?

3) The starboard side manifold and riser on both engines is noticeably hotter to the touch than the port sides. On the starboard engine you can keep your hand on it but it's hot. On the port engine it would be uncomfortable to keep your hand on it for more than about 5 seconds. Again I've read that some think these engine always have hotter manifolds on the starboard side for some reason..........related to the water flow design I guess? Is it normal for these engine to have hotter exhaust on the starboard side and if so how hot? Should I be able to keep my hand on the risers for a long time?

4) The port engine has a hard start problem after sitting for awhile. It will crank and want to light but not quite fire up until running it over on the starter for awhile. It does have good fuel pressure while this is happening (42 psi). Two other symptoms are that once it starts it runs rough for maybe 10-15 seconds and two times I noticed there was little or no water flow from the exhaust right away after it started. Not sure what that is telling me..............if anything? After it does start it sounds like there is a bunch of airflow going thru the IAC until it closes up so it seems that the IAC is at least moving and maybe that explains the rough running? I haven't dug any deeper on this, pulled anything apart, or scanned it yet but that is next. All I've checked so far is fuel psi while this is happening and it is good at 42 psi. Any ideas?

Beyond that it has new Hardin stainless water pumps, new plugs / caps / rotors, new t-stats, drives where gone thru and checked out my the Merc service place.

Does this stuff add up to obvious signs that the manifolds need to be replaced? The old plugs came out clean (no rust on them from in the chamber) and the oil had no signs of water or milking. Any opinions or ideas are appreciated.

Thanks, Pat

Anybody?

Stock 502's came with 160-degree T-stats. P/N: 807252T2
200 is much too hot. If you're seeing 200 with 180 t-stats, it sounds like you have some restrictions in the water passages. The primary culprits are most likely the manifolds or your drive's seawater supply passage. Also back flush the system eliminating the possibility that there isn't any debris clogging up the water passage exits from shredded pieces of old impellers.

The photo shows what a typical saltwater-use drive passage looks like after a few years. The I.D. is about half of what it was new, and usually contributes to overheating, and starving pumps for water.

Your hard-start condition sounds like vapor lock to me and an overheated engine could be a potential cause. See here:
http://www.offshoreonly.com/forums/g...apor-lock.html

Thanks for the reply.

I'll have to investigate the water feed passage in the drive. Pretty sure that the t-stats I got from the Merc dealer where 180's so I'll switch to the 160's for sure.

I feel like I'm on borrowed time with the manifolds and was hoping to get this season out of them then replace them with SSM's over next winter. Wasn't sure if I was being paranoid or this stuff adds up to sure signs that the manifolds are on the way out and won't last the season? I guess I really won't know until it's too late and leaving them now I know I'm taking a chance. Should the risers stay relatively cool to the touch and normaly be around the same temps on both sides of the engines?

As far as the hard start issue I agree that it acts like vapor lock but it happens at the oposite time than you'd expect to see a vapor lock problem. The hard start happens on the first cold start up after the boat has been sitting for a few days or after sitting on the anchor for half a day, not while hot or after it sees extended heating in the engine compartment. It does have good fuel pressure while this is happening also so I'm not thinking it's a pump issue. Starting to think it may be a fuel tank or fuel condition issue. The boat has seperate tanks for each engine and the starboard side doesn't have a problem. There was around 40 gallons of old fuel in each tank from the last owner left over from last year (supposedly with stabilizer) and I toped it off with another 80 of fresh fuel in each tank figuring it would be OK.............maybe not?

I was trying to get a handle on if there was any manifold related things that could cause this hard start because as I said I did notice that there was a lack of water flow from the exhaust when it finally did start a couple times this happened. All I could think of was enough water draining down from the exhaust into the engine to wet the plugs and cause a start problem but not so much that it would hydrolock??.............but I think that's kind of a stretch. Also the oil level and condition are good and the plugs aren't rusty so that leads me away from water in the chambers. Don't know.............the lack of water from the exhaust just those couple times has me stumped. I have that feeling that I'm missing it and when it goes boom I'll look back and realize it was telling me something and I wasn't listening

Thanks again, Pat