454 mercruiser running hot "update"

i hate to say it...but you may have just exposed a separate problem.

i re-read your original posting. did you ever check the risers for clogged water exit holes and passages. without good out-flow, you're gonna run hot, too.

sorry i ain't got no capital letters...spilled some liquid on the keyboard.
 
Have you ever:
1) taken the raw water hose off of the exchanger and tested the raw water flow coming out of the impeller?
2) tested the pressure cap for the heat exchanger to see if it holds pressure?
3) pressure tested the closed side of the system, to see if it holds pressure?

reason why I ask is that I had a problem of gradually increasing engine temps, that persisted despite a new impeller, new thermostat, clean risers, etc. I put the boat in the water and disconnected the raw water intake hose at the thermo housing. Low flow for sure. It turned out to be barnacles growing on the water intake screen in the lower unit. I wound up splitting the drive to clean out the water intake area and that dropped the temp from 170-185 back down to 160 where it should be. This is the most basic test of a marine cooling system, be it raw water cooling or closed cooling. You need a lot of flow in (impeller, water intakes)and a lot of flow out (risers) for them to run at normal temps.

Any coolant leaks? You really need to find out if the cooling system holds pressure, because under the high load of pushing that heavy boat through the water, the coolant will get hotter than it should if the cooling system does not hold enough pressure. The pressurization of a cooling system is what allows higher temps without boiling the coolant. The aeration of the coolant,due to localized boiling, will cause the temps to rise.

Lastly, air leaks in the raw water intake line, could also cause overheating. This can be checked by putting a section of clear reinforced hose in the line that goes from the transom to the impeller (temporary for test purposes). You'd have to have a helper watch to see if there are bubbles in the cooling water. You've done the exchanger and the risers but there is more to check.

About the check balls in the thermo housing, they are used in the Merc raw water cooled housings but I don't think the thermo housings supplied with the closed cooling kits have them.

The single most important thing is the actual raw water flow to your heat exchanger and the flow out the risers. If your raw water flow is low, you will have exactly what you note, normal temps at light load and increasing temps at higher load of running the boat on plane.
 
W E L L L L, DR confirmed it, have a broke rib and a seperated collar bone, oh joy what fun this is!

I have taken both risers off, soaked in CLR, had one of them ground due to some water intrusion into the manafold. They were not blocked though. There was some of the same white rock sitting on top of the gaskets, but really not that much.

I have pressure tested the closed side and it holds pressure, no leaks either.

But, I did find something on the oil cooler while I was down there, the outlet clamp was not tight, really not tight, like slid down the hose not tight, and I did fix that. Not sure if I was sucking air or not, but no leaks while sitting, in fact the bilge stays dry after being in the water for a few weeks.

Shop vac got most of the oil out, but I do have some pigs in there for the rest of it.

I had the admiral start the engine up while I was in there and I did not hear any thing unusual, but, I did not run it but a few seconds while I pined the leak down, so not sure yet if there is damage or not, I feel not as it started and ran too good, with out any unusual noises.

I have not pulled the raw water hose off, but flow from the out drive looks really good. I am really leaning towards the engine just likes to be at 200, which is really not that hot. My 4.3 vortech runs at 210, and that is normal for it.......D........
 
yeah, that could be it. last, last engine rebuild (I rebuild my engine at the drop of a hat looking for the right power setting...but that's another story) i had all new parts but 3 new thermostats had my engine running in the 200-210 range at certain speeds. i picked the coolest thermostat and kept an eye on the temps. it slowly came down to the 180 area.

the same thing is happening again but the cause this time is my ss and fully water-jacketed exhaust system. the cause is my outlet holes are just a touch too big which is letting the water drain out too fast. doesn't sound logical but it's not the first time i re-adjusted the size of the exit holes...which on stock systems is the little exit hole at the bottom of the riser.
 
What company made the closed cooling system? Do you know for if the heat exchanger is big enough for the engine? I'd see if I could call the company's tech support, and ask them if it's big enough for a 454.
I'd still like to see if that raw water flow matches Merc's spec. I've never had a closed system on an inboard so I don't know for sure what temps they run at. Of course they can run hotter than the rating of the thermostat (160*) with no engine damage but in a marine application I'd be a bit concerned of 200 or slightly above due to the constant load that a marine engine has. My old '98 Jeep used to run a bit hot in really hot conditions, traffic temps over 90*. It is supposed to run at 210, but was getting to about 220-230 in heavy traffic.
I had replaced the rad and water pump, same temps. Finally I replaced the old fan clutch with an aftermarket HD unit. That is what made the difference, now no matter how hot it gets, it stays at 210* like it is supposed to. Since the old '98 does a fair amount of beach driving, both that fan clutch and the B&M trans cooler helped it out a lot.
 
It is probably made by mercury, all the other external exchangers are made by them. Cant say for sure as it has no real marking for a manf. It looks to be original to the boat, it does not appear to be an add on or after thought. Also cant say for sure if it is big enough, all I have to go y is what others say with similiar engines that thiers run at 200 also.........D.........
 
San Juan makes most of the HE. The 4"/4 pass is the biggest that I've seen on mercs.
 
For sure I'd call San Juan and find out if that's big enough for your engine. Does your system include the manifolds or are they raw water cooled? That makes a big difference, if they are on the closed side then you need the bigger heat exchanger.
Does Merc give any spec for proper operating temps for their closed systems? I know when you have raw water cooling with a 160 stat, your operating temps are between 160 and 175 but not more than that if everything is OK. Mine runs at 160 most of the time, it will go up to 175 if you come off plane but then cools back to 160.

I read through this from Monitor systems, it has a lot of good information. According to them the temp should be betwen 160-180 but not over 185..

http://www.monitorpro.com/Editor/assets/General Manual rev01.pdf
 
I'm not sure if I mentioned it to you or maybe you read it,but, Full Freshwater cooling should have a thru-hull pick-up as well as the drive pick-up. The drive pick-up is important because it helps cool the drive but the hoses are not very big. A thru-hull with 1 1/4" to 1 1/2" hose will draw lots more water.
 
To the best of my knowledge right now, I only have the drive pick ups, I dont know of any through hull pick ups, but will check the next time I have it out of the water. Each time I have ran it on the trailer, I have ran it on muffs and never noticed any other points.

I read through the PDF above and will check some of what I havent already. Hopefully the oil return hose will be in friday and I can take her back again, thats if this rib and collar bone will allow me to put it back in....D..........
 
4 pass has one separater on the far end and two on the near end...another way to id it is the 'in' and 'out' are on the same end. a 3 pas would have to have the 'in and 'out' on opposite ends.
 
D
I am not familiar with the cooling system on a boat that has an outdrive, but will tell you I had the EXACT same problem on a Crusader 8.1 motor with straight drives. I replaced risers, acid cleaned the heat ex changer, etc, etc, same problem. Inspected the impeller early on and just for the heck of it replaced it, same problem!. Long story short, It was the water pump :(
Inside the water pump, the shape where the impeller rides in the housing is oblong, apparently although on a visual inspection it looked perfect, it was not. What happened was the housing wore down and could not keep up with the water flow needed when I was at cruise rpm which in turn would make the motor run 20 degrees warmer. Also, at idle or slow speeds when looking at the water dumping from the exhaust it looked fine. Would never of guessed it was the pump.

Walter
 
This is why I said, always verify raw water flow in, and flow out first. Worn wear plates, or impeller housings, will prevent the pump from flowing enough water at above idle speeds. Whether is raw or closed cooling, these systems depend on high volume of water in and out.
To give you an idea of what OMC's spec is, you put the boat in the water, disconnect the hose from the impeller, have someone hold the hose up, it should give a 2-4" head of water. Look up what Merc says.
 
Lou- My understanding is the opposite of what I think you are saying.

Generally speaking, worn wear plates and housings have greatest detrimental effect at idle and low rpm while the impeller tips still swipe against those parts to create the necessary suction. Any wear surface (including impeller) grooving breaks that low rpm suction. At higher rpm the vanes are no longer contacting those surfaces and the pump is just acting as a centrifugal pump, plus in-gear forward motion adds the ram effect at the intake.

It is possible housing wear can be great enough that higher rpm flow could be noticeably compromised , but in that case I should think idle cooling flow would already have been extremely poor. Most often, poor pump performance at higher rpm is due to impeller damage.

All that said, sometimes housing/wear plates and especially impellers (slightly off hub placement,for instance) are imperfect and can be a little frustrating to track down since they look so good.
 
Well, overheating is the least of my worries now. Apparently spun a bearing when the oil hose blew. Got the new hose installed this morning and took it for a very short trip, sounded fine at the slip, ran it for about 30 minutes, no sign of any issues. as soon as we got out of the marina and I started to power up, there is was, engine was clattering and no real performance, puttered back into the slip. Will take the trailer back out in the morning and pull it home. Going to have to pull the engine now. Guess I will figure out the over temp while I have it apart.......D..........
 
So as some know I have to rebuild the engine. So while it is out, I am going over the wiring, painting the engine room, hoses, lines, etc. So today I pull the water heater. The electric part of it quit working the last time out so I figured the element was bad, so was going to pull it, paint where it mounts, etc. So out she came, and there it was, the reason for the over heat. Not only is it electric, but it has a heat exchanger built in to take engine heat and heat the water, this is part of the engine cooling circut. It has what looks like a plastic coating inside and outside of the lines going into it, one of them, the plastic has broken down and almost closed off one of the lines, there was only a very small hole in it. Concidering it is part of the cooling circut, this has got to be the cause. It is on the anti-freeze side of it, which would no doubt restrict the flow........D.........
 
Dave- While it is a terrible shame the engine needs the rebuilding, it is a really, really wonderful thing you have apparently finally discovered the main culprit BEFORE the rebuilt engine is installed and run. Good find!

May the news be all good going forward....
 
Dave,
Is there a way to tell if the heater is on a bypass circuit or directly tied in to the exit flow from the heat exchanger?
 
Directly tied, not on a bypass. I am thinking of installing a bypass for it prior to install, and am going to eliminate the front heater core we never use anyway. It is in the front of the cabin and we have never turned it on. Heat and ac were added later so I really dont need it.........D.........
 
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