another mercruiser overheating!!

[Lazy Daze]

I am unsure. But, until we can get a definitive answer, I'll offer my 2 cents... although it really only has a street value of about 1.1 cents right now...

As the years have gone by, engine efficiency has become more and more of an issue. One of the ways to increase efficiency is to run an engine a little hotter. That part is quite evident from looking at what stat is required for the engines as the newer ones require a hotter stat. But, that would also entail a better cooling system to keep the engine in it's "peak" efficiency range and not allow it to get too hot or too cold.

So, yes, I think you're at the right tree - but again, this is just me "thinking out loud".

 

[steve930]

Do you have a phone number for mercruiser technical over there? Theres not much knowledge/backup over here in the uk.Assuming I'm At the right tree, changing to the later stat housing would involve blanking off the water pipes to the risers & fitting the 4 large hole riser gaskets?

 

[Lazy Daze]

You could try contacting Merc at 920-929-5040, but they may tell you to contact a dealer. It's at least worth a shot.

As far as your risers go, I think all would need to do is remove the nipple and screw in a plug? Maybe I'm missing something (haven't done this before), but I don't think you'd have to change the gasket. But again, not sure on this one.

The only other thing you may/may not have to do is change to different hoses if the current ones don't mate up to the newer housing.

The other question would be whether or not the new housing will mate to the intake manifold. It may, I just haven't done it or looked that closely at it to know.

 

[steve930]

thanks for the number, I phoned them but it was more like talking to a politician than a tech guy!! He said it shouldn't be a problem running gen2 leg with early thermostat housing, but couldn't commit to this without me giving him the serial No's of the engine & leg.

Trouble is my boat originally had the 300 engine & when it was re-engined it was fitted with the 350 it has now, the leg no longer has the plate where the serial number is printed, plus as the boat is in the water i can't read it anyway :smt021. But how relevant this is to a simple question i don't know, He then went on to say that they recommend (where possible) to fit their latest style of thermostat housing!!

So on that basis i think i will order whichever housing is the cheapest!

 

[Lazy Daze]

Yeah, everyone's afraid to commit to something when the answer isn't "black and white". But, I guess you can't blame them too much seeing as how "sue happy" people are.

The t-stat housing style that's used on my engine (from '99) might work for you - if it mates correctly to your intake, that is. But, assuming you have a new intake and the old housing mates up, I would think it would work? Mine's a simple 4-hose setup.

 

[steve930]

yeah gonna do some more research on this tomorrow ( it's nearly 1am over here) The only stumbling block, is when mercruiser started using the vortec series engines as i know the heads/inlet manifold are different and quite possibly the thermostat housing

Once again thanks for your help/input on this dennis, i really do appreciate it

cheers, steve.

 

[andyr]

I have had the bonding fail on two impellers. It shows plenty of water at test but when reved up under load, the impeller slipped around the metal sleeve causing an overheat at high rpm. A good test is to hook up a section of clear tube between the thermostat and supply hose from the drive. Bubbles are bad. Rev it and then see bubbles - bad. When replacing the impeller, did you also replace the housing? It can let air in and cavitation. Also, the internal passage in the thermostat will scale up and cause high rpm overheat. The ball springs only cause overheat at low rpm. Lastly, when on plane, the pump may be above water. Air can get in at the hose fitting in the transom if cracked.

 

[Lazy Daze]

yeah gonna do some more research on this tomorrow ( it's nearly 1am over here) The only stumbling block, is when mercruiser started using the vortec series engines as i know the heads/inlet manifold are different and quite possibly the thermostat housing

Once again thanks for your help/input on this dennis, i really do appreciate it

cheers, steve.

I'm not sure exactly on the year, either. But for some reason '96 or '97 sticks in my head? Tell you what... I probably can't get to it tell the weekend, but why don't we compare the housing mating surface of the intake manifold between yours and mine? If you want, take a picture or two of the "hole" and put a ruler or two in the picture for reference.

No problem with the help! I know how frustrating things can be. If for nothing else, just bouncing ideas off others can help.

Andy is correct that a weak spring will cause an overheat at low RPM's. But it's something that is easy enough to check... And who knows... I've seen weirder things.

 

[steve930]

Right, I've done some research! . The spring loaded ball style stat housing was used from 1983 - 1993. Obviously the gen2 leg was launched in 1991 which would confirm that its ok to run gen2 with this housing.

I've found no concrete evidence suggesting that I would be better off running with a later style housing, I believe if anything the engine runs slightly warmer with the later type to improve engine efficiency.

The only issue regarding leg water flow rates & types of thermostat housing is between the alpha & newer bravo legs.

Based on all of the above I'm gonna order the original spring ball housing. If not just for simplicity, but because I don't think its causing an overheat issue, its just 20+ years old & in poor condition/will fail soon!

I'll get this ordered fit it & carry on trying to solve the original issue (unless by some miracle it cures the problem)

Thanks dennis for the kind offer on the measurements

Cheers steve.

 

[Lazy Daze]

No problem, at all, Steve. I enjoy this kind of thing. Keep us posted.

Right, I've done some research! . The spring loaded ball style stat housing was used from 1983 - 1993. Obviously the gen2 leg was launched in 1991 which would confirm that its ok to run gen2 with this housing.

To play devil's advocate a little bit.... Or, the fact that Merc changed the housing style after two years could indicate that they were finding overheating problems in the field and changed the housing design.

I'm not one to second guess engineers as they know more about this stuff than me. But, it does make wonder why there has been so many different designs over the years. For example, even though they dropped the ball/spring design, some newer engines have been using it again!

I'm not trying to convince you to change housing designs - just offering a competing line of thinking, which may very well be wrong.

 

[CliffA]

I'm not one to second guess engineers as they know more about this stuff than me. But, it does make wonder why there has been so many different designs over the years.

i agree...i'm still not sure why the right and left exhaust risers heat up to different temps when the engine is running...almost every post i have read on this states that one exhaust runs hotter than the other...my starboard exhaust runs about 25*F hotter than the port exhaust....looks like the cooling water circulation flow could be designed to maintain fairly even temps across both sides of the exhaust....

cliff

 

[Lazy Daze]

i agree...i'm still not sure why the right and left exhaust risers heat up to different temps when the engine is running...almost every post i have read on this states that one exhaust runs hotter than the other...my starboard exhaust runs about 25*F hotter than the port exhaust....looks like the cooling water circulation flow could be designed to maintain fairly even temps across both sides of the exhaust....

cliff

That's correct - a small difference is normal. This one just comes down to "path of least resistance". Turbulence of the water moving through the housing... the boat rocking, allowing the engine to lean one way or the other... possibly even a slight difference in height from one side to the other due to engine mounts.

The turbulence could be addressed with a better housing design, but the truth is that it really doesn't need it. In a properly maintained and operating system, everything is A-OK.

Heck, if you took measurements at various spots of the block and compared it the other side, you'd likely even see differences, or "hot spots" (whether marine or automotive). It's kind of just the "nature of the beast".

If you're ever running on hose and the boat/trailer is listing, you'll also notice that water comes out one of the exhaust ports much more so than the other. In addition to the above reasons, that's also due to the way the water moves through the y-pipe (again, path of least resistance).

 

[steve930]

No problem, at all, Steve. I enjoy this kind of thing. Keep us posted.



To play devil's advocate a little bit.... Or, the fact that Merc changed the housing style after two years could indicate that they were finding overheating problems in the field and changed the housing design.

I'm not one to second guess engineers as they know more about this stuff than me. But, it does make wonder why there has been so many different designs over the years. For example, even though they dropped the ball/spring design, some newer engines have been using it again!

I'm not trying to convince you to change housing designs - just offering a competing line of thinking, which may very well be wrong.

I know where you're coming from dennis, i was having the same thoughts but my new found rationale is, i can't imagine mercruiser would run with a component that was causing overheating problems for 3years (just imagine the potential for warranty claims over that period of time) If there was an issue i would've thought it would come to light/be resolved within a year?

Secondly that style of housing has been in use now for nearly 30 years, and is still avaliable to buy new, whilst doing all my research earlier today the only reported problems i could find relating to this housing are the well broadcast issue with the spring balls not seating properly/or slack causing overheating at idle speed, but certainly no issues with overheating whilst at high revs

I'm no engineer and could well be talking a load of tosh, :grin::grin:

 

[Lazy Daze]

Good points, Steve.

I'll make one last point about this and then shut up... Can that housing design support enough water flow for the newer-designed engines and fuel injection/hotter stat? If you're going to buy a new housing, why not get a newer design? I mean, if you're going to spend the money, anyway?

OK, I'm done. Back to hoping that you get it figured out and let us know your progress.

If you can, I'd still be curious to know what the top of your risers feel like (with your hand). I'm just wondering if the engine is, indeed, getting hot - or is it just registering hot at the sensor.

 

[steve930]

Its too late dennis, I've ordered the new housing, along with 140 &160f stats as well as gaskets for water circ pump (so I can remove & inspect properly) and also some riser gaskets. All ordered from usa so should be with me late next week.

If it wasn't for the fact that I replaced ALL the rubber hoses on the engine in 2011 then I wouldn't have minded updating to the newer stat housing (i purchased all the correct mercruiser moulded hoses not cheap!)

As a side thought it might be interesting to remove the Tpiece/balls & blank the hole & do the same on the risers, so in effect going from a 4 pipe system down to a 2 pipe system like the later stat housing and see if & what difference it makes to running temps.

As soon as I can get out on the boat I will check the temps on the risers. We are having 25+ mph winds over here at the minute and during the week I'd be on my own so its a nightmare trying to moor her up!

Cheers, steve

 

[steve930]

small update.

Still waiting for ordered parts to arrive, I've not had time to get to boat yet, but am hoping to go down on sunday if not then one day in the week seeing as i have a few days off next week. I have got my temp gun back now, so when i go down i'll take her out for a run & do the hand on riser test as well as get some actual readings.

Of more interest i've managed to track down the mechanic who looked after the boat for the previous owner. He was the one that changed the engine & the leg. He said that the previous owner used the boat 6 or 7 times with the new engine/leg before his health problems & on 1 occasion it had an overheat issue which turned out to be a faulty thermostat. Doug the mechanic replaced this & sea trialed the boat for approx 20 miles at all engine revs etc etc and the temps remained good & stable.

I think this just finally puts my mind at rest about the type of stat housing currently fitted.

 

[Lazy Daze]

I think this just finally puts my mind at rest about the type of stat housing currently fitted.

That's good to hear, Steve.

if the stat is in correctly (and the plastic spacer), you could check the stat in a pot of water. Suspend the stat and turn the heat on. Using a thermometer in the water, you can observe when it opens.

 

[steve930]

When i fit the new stat housing i will check the current one in a cup of water as you say, i'm pretty sure its ok though because when the engine reaches stat opening tempreture, i can tell its opening because hot water gets released down the pipe to the hot water calorifier

 

[2000SEARAY280SS]

there was a post back in this thread that talked about air getting into the system and causing problems. i had an overheating problem that i traced all over when i first got the boat. went through all the steps you are doing and it was not until my wife was able to get in the bilge and tighten this clamp up about 5 turns of the screw driver did the issue go away. here is a picture of the transom transition from the out drive to the water pump.

check all of you clamps on the suction side of the pump and make sure they are tight. especially since you replaced your hoses you might have a bad clamp.

 

[steve930]

there was a post back in this thread that talked about air getting into the system and causing problems. i had an overheating problem that i traced all over when i first got the boat. went through all the steps you are doing and it was not until my wife was able to get in the bilge and tighten this clamp up about 5 turns of the screw driver did the issue go away. here is a picture of the transom transition from the out drive to the water pump.

check all of you clamps on the suction side of the pump and make sure they are tight. especially since you replaced your hoses you might have a bad clamp.

Thanks for the suggestion, I will double check it,

when i replaced that pipe the new one came with a new adaptor & i installed both the size adaptor & pipe with bellows adhesive There's no water leaking from there so i'd assume if water can't get out, then air can't get in