Uneven temps, at my wits end!
 

After chasing the reason for why my starboard riser is running about 30 degrees hotter then port, and blowing steam, for about a year, I found something interesting.

1999 502 MPI, Bravo 1
New within last 1.5 years:
Manifolds
Risers
Replaced riser/manifold gasket on problem side 3x, filed mating surfaces to make sure they were true
Raw water impeller and housing
Circulating pump
T-stat

Thinking it's a water flow problem, today I decided to start pulling hoses. Pulled both hoses that feed the bottom of the manifolds off at the tstat housing. Started engine (it was cold), had even flow coming out of each end of housing. Reinstalled the hoses and let engine come up to temp (+/- 165). Shut down and immediately removed the same hoses from the tstat housing and had friend restart motor while it was hot. While holding my hand a few inches from each side of the housing to feel the flow rate (as I had when the engine was cold) and see if it was still even to port and starboard after the tstat opened, the water coming to the starboard side just about burned me, while the port side was basically lake temperature. I'm talking a major difference here. So, that solves my problem of why my one riser and manifold are so much hotter. Pulled tstat housing and explored with a scope, but I honestly wasn't sure what I should be looking for. Just ordered a new housing.

Any clues why or how this would happen? It seems that all the hot water being discharged was sent to the starboard side rather then being distributed evenly. I'm really hoping someone says that the tstat housing is obviously corroded or there is a blockage of some sort....I've had enough of this...

when you changed the t-stat,did you use one for marine use?

Now im really going to upset you after all that work .

Its normal

I have seen MANY MANY boats like this. My buddies does it after a fresh BBC, my boat does it aswell, with fresh thunder risers, pipes. Is it normal, hard to say, but again I have seen a bunch like this. I would be curious to know why aswell, never bothered me, so I never really checked into it

John jr

It's a Merc t-stat

Guys, listen, if it's normal then I'm one happy bastard cause I can forget about it. It's just that it wasn't always like this and seems ludicrous to me that I'd be dumping all the hot water out of one side and the cool out of the other. Lots of friends with the same motor don't have this issue.

Anyway, I'm going to put the new tstat housing on for piece of mind and see what happens. By the way, I found it for $135 on ebay, it's a brand new take-off.

fixx
 

when you installed # 6 what position did you install it? also make sure you install a hp thermostat with the bypass built into it..

http://www.google.com/imgres?q=1999+...x3Ki3Cg&zoom=1

when installing #6 you can turn it to direct the water to favor one port or the other,in your case i would slightly turn the colder side towards the warmer side and see if that helps with the steam..

I installed exactly as in the diagram. You're saying to rotate it a bit to direct more cold water to starboard, right? So, looking down at it from the top, do you know if I would rotate it clockwise or counter clockwise?

fixx
 

..you could also leave it straight up and put a hose clamp on the colder hose for trial and error to see it it takes away the stram,,kinda like restricting the water going to the cooler side and forcing it towards the warmer side..

mercruiser phucked up when they got rid of the cooling balls rod and springs..

Question - What method are you using to measure the temp, are you using a "laser temperature gun", if so measure the temps at the front of the manifold and at the rear of the manifold. It is my understanding that some temp variation is going to be normal form left to right manifolds. I saw a thread on here quite some time ago where a gentleman had a similar problem. I believe the gentleman solved it by increasing water circulation in the back of the block by modifying his intake manifold, installing hoses from the rear of the manifold water passages to the either the risers or to the thermostat housing, can't remember which, but the idea is to have the water exit the rear of the block, where steam pockets can develop. I know that some people do this modification and then have the water dump overboard. Hope that this helps.
Cliff

Yea there's actually a groove on the housing and ridge on the sleeve so I can't adjust the position. It only fits one way.

I've been chasing this same ghost for a couple of weeks. Sucked up some sand, clogged system, then overheated (slightly). So while flushing the P/S and oil coolers, I noticed that the starboard riser was much hotter than port - by 40 ~ 50 degrees average. So I reflushed and reflushed and ... scratched my head and cussed and....

I don't believe in ghosts so I've tried to forget about it. Haven't melted anything yet.

Port - about 105 degrees running
Star - about 150 degrees running

I'm putting the new housing on next week and will see what happens. The old one seems to have a good amount of rust and scaling, possibly some partially blocked passages.

After that - I give up. After all, even the hot riser is running around 138 degrees, it's not near cracking temperature. I've read on several sites that anything under 160 or so is fine.

Update:
Decided to use clear hoses from tstat housing to each manifold. Noticed minimal bubbles on the side that was running cooler, and much more on the side that was running hotter. Took the hose that should feed the port manifold and moved it to starboard and vice versa, and the problem flipped to the other side.

So, do you think there's a chance that I have a small crack in my tstat housing that is introducing air as the water exits the housing? I would think that if the air was being introduced anywhere prior to the tstat housing, then the air bubbles should be coming out evenly from the housing to both manifolds, no? Mine is not even at all, one side is getting much more air bubbles and that side riser is running hotter and blowing steam.

I too have had this issue for basically forever on my 502, changed parts, did all sorts of things and never found the "issue" as others have said I think it's normal (or maybe that a nice way of saying that I gave up :)). I see about a 25-30 degree temp difference and the starboard side of my engine kick out tons of steam compared to the port, best friends formulae 232 (stock 454/330) is exactly the same as mine. As long as you have good water flow, I wouldn't worry about it to much. Though someone here may say different and have a great idea that I wan't able to sort out. I too was able to make it swap sides FWIW.

As far as the bubble issue, that may be something entirely different.

here is a possible cure. get a 4-way adaptor fitting. run both inlets in and both outlets out. then the water will mix and even it out. if you don't like the way it looks, don't open the hatch...

my best guess is casting inside directing flow to one side over the other, i have noticed this in older tee with control balls but not as much temp difference. the rear water passage trick is same as done on 6.2/6.5 diesels. tap holes into rear of intake; most intakes have dimples already. and put fitting and hose, either to overboard discharge or to t-stat spacer that cpperformance sells. allows air to vent rather than travel thru heads.