Weak Water Flow Causing Overheating?-gctid390349

[Guest]

I have an overheating problem with my boat - Mercruiser 454 (7.4L) with a first Gen Alpha One (1987). I have had it in the water once, and the temperature shot up over 200 just as I left the dock, setting off the alarm. As I was maneuvering back to the dock, the alarm stopped, and the temperature returned to normal. I ventured out and eventually had a full boating day with no overheat issues whatsoever.

Back on the trailer, on the muffs, the engine overheated again. I checked the flow at the end of the hose coming from the outdrive inlet to the steering cooler, and it is a slow flow. At the thermostat inlet, it pulses. I checked the thermostat in hot water and it works fine, so I put it back in. I suspect a weak flow of water that exits to the exhaust manifold and does not flow through the block.

The outdrive is old and corroded. I replaced the impeller with a full rebuild kit, and put as sealant on the gasket under the pump base. The old impeller looked fine. I tested again and the problem is the same. I see no kinks in the hose feeding from the outdrive to the stern, or from the stern to the water pump cooler.

The engine was just rebuilt 9 hours ago. The P.O. had it in the water, and never had an overheat problem. When I ran it that first day in the water, it worked well after the initial overheat. I wonder if the pump is sucking air somewhere on the muffs, an area that gets flooded after it sits in the water for some time. Any ideas for troubleshooting? Is there a pump drive gear that could be bad? Any likely place air could be ruining the pump draw?

[Guest]

Have you checked the manifold and risers for obstructions? Were they reused when the engine was rebuilt or are they new? What about the flappers? One or both could be stuck in the closed position or become dislodged and blocking the passageway.

[Guest]

2859er wrote:
... One or both could be stuck in the closed position or become dislodged and blocking the passageway.

They were reused. I thought the P.O. said something about "reving it" to free up something in the exhaust. Are you suggesting this is putting backpressure in the cooling system?

[Guest]

wildman wrote:
They were reused. I thought the P.O. said something about "reving it" to free up something in the exhaust. Are you suggesting this is putting backpressure in the cooling system?

If the manifold and risers were reused then there is a big possibility that there are blockages. I see you boat in salt water. Rust and scale can build up in the water passages closing off or limiting the water flow.

If the flappers were reused they may have deteriorated to the point that one or both may be blocking the water and exhaust flow as well.

You may have to take the manifolds and risers off off and have a look see. While they are off you can look down the Y-pipe and check out the flappers.

[Guest]

wildman wrote:
.... I checked the flow at the end of the hose coming from the outdrive inlet to the steering cooler, and it is a slow flow. At the thermostat inlet, it pulses....

I am starting to wonder if this is normal for a 1st gen Alpha One. It has the old pump style.

[Guest]

Just so it is clear in my mind what might be happening with the water flow, first look at the diagrams attached. I know that water is getting to the thermostat housing. I am pretty sure when I did my troubleshooting that, after the engine warmed up, water was coming out of the "to exhaust manifolds" section, after the thermostat opened.I could see that if the manifold passages were blocked or back-pressured, it could stop the flow. But if I disconnected those hoses going to the exhaust manifolds (not the elbow) that water would be flowing through the block and it should cool down? I have not tried this, but shouldn't a test like that work, proving that the problem is blockage after the thermo housing?Also, can I still get Thermomelt sticks in this era of IR heat sensing guns? I assume they are cheap?

[img]/media/kunena/attachments/vb/694279=28633-cooling_merc454_fresh_ 005.jpg[/img]

[img]/media/kunena/attachments/vb/694279=28632-cooling_merc454_fresh_ 001.jpg[/img]

[Guest]

The more I think this through, the blocked manifold / elbow theory does not add up to me. Why would it operate fine the day I had it in the water, after the initial overheating problem? Why did the previous owner not have any problems? Why would a mechanic put plugged manifolds back on an engine he just rebuilt?I did some more research today and suspect parts 3-6 on the attached diagram.

[img]/media/kunena/attachments/vb/694689=28689-mercruiser_87-89_454_thousing_new.jpg[/img]photo courtesy of www.marinepartsexpress.com - a great site!

[2850Bounty]

wildman wrote:


The outdrive is old and corroded. I replaced the impeller with a full rebuild kit, and put as sealant on the gasket under the pump base. The old impeller looked fine. I tested again and the problem is the same. I see no kinks in the hose feeding from the outdrive to the stern, or from the stern to the water pump cooler.

The engine was just rebuilt 9 hours ago. The P.O. had it in the water, and never had an overheat problem. When I ran it that first day in the water, it worked well after the initial overheat. I wonder if the pump is sucking air somewhere on the muffs, an area that gets flooded after it sits in the water for some time. Any ideas for troubleshooting? Is there a pump drive gear that could be bad? Any likely place air could be ruining the pump draw?

I'm not too crazy to see a Big Block relying on an Alpha drive sea water pump for cooling.

Why this is intermitant, I can't quite explain.

wildman wrote:
I did some more research today and suspect parts 3-6 on the attached diagram.

Dave, if the two hoses at/near the ball valves are being compressed into (or have become smaller in diameter) at the area that the balls need to operate within, it may be restricting ball movement, and it may be part of all of your problem.

I don't know for sure.

Merc also uses a configuration whereby the T-stat housing is a twin outlet only.... (not a double twin outlet).

This system feeds the exhaust manifolds from a single point, then uses the manifold-to-riser transfer ports for the bulk of the spent sea water.

In this arrangement, the restrictor plates are NOT used, and the riser feeds are blocked off, making the maniolds receive "first water", and then up and out via the risers.

This is what Merc does for some SBC's, and is similar to what Volvo Penta does for all AQ series BBC's and SBC's.



Have you checked the inlet side of the P/S oil cooler for any debris????

Have you looked at the short hose that joins the Gimbal Bell to the transom housing???

I'm finding it odd that the legend in this schematic shows cold (white arrow) and warm (dark arrow) water flow, yet all of the arrows indicate "cold".

Not that it matters..... just odd!



If I was chasing down this problem, I'd begin at the out drive and sea water pump.

I'd then work my way forward, and would check each item in-line with the sea water path, eliminating or discovering one item at a time, until I found the problem area.

P of E..... (process of elimination).

When done systematically and methodically, it will never fail you.

.

[Guest]

I am editing this post, because I found the problem and it was the checkballs!. My t-stat housing really is like the one in the parts diagram. I read on another forum that the springs get weak, and you have to spread them so they are springy again (thats right, the springs need to be stronger so the checkballs need more pressure to push them open). I did this and it solved the problem. I was sitting in the engine compartment looking at the setup. I knew that water was flowing, so it should pass through the engine block. Unless ... water was choosing to flow through the "T" to the elbows instead of through the thermostat and to the manifolds. Also, I know sometimes cooling systems need to pressurize. So I checked the "T", and there were the checkballs!

My original post that follows is wrong wrong wrong! :

Looking at the I did some troubleshooting today but I am still stumped. My t-stat housing did not have a checkball like the parts diagram I posted. It appears to be setup like the image shown in my Clymer manual:One exception is a smaller hose that runs from the t-stat housing to the top of the engine water pump.I ended up removing the thermostat as a test. I ran the engine and again it overheated.Then, I removed the hoses going from the thermostat cover to the manifolds. Water flowed out of the t-stat housing (into the bilge) and the temp stayed at 160! Note: when those hoses are removed, water stops flowing out of the outdrive (but the elbows stay cool).I am ready to look at the manifolds, like 2859er said, but I wonder: since water readily flows to the outdrive with the hoses to the manifolds connected, how could there be blockage?Any ideas? Anybody?

[TerryW]

Any ideas? Anybody?

Rick has it 99% covered but here are a few ideas from someone who lost a whole season when a dodgy engineer wrecked his waterflow . . .

a) If you are gonna start changing stuff, change the cheap stuff first (and keep reusable parts for spares). Thermostats, senders, gauges, flappers etc are cheap compared to exhausts anyway.

b) A cheap and easy diagnostic tool is a length of transparent hose that you temporarily "plumb" into the line from the water inlet coming from the outdrive. You can watch for bubbles, color of the water and speed of flow (you always get minute bubbles by the way). I got mine from an outdoor aquatics shop. I resisted the temptation to buy a goldfish.

c) Make sure you are really overheating. Use an IR temperature gun or a carefully placed hand. I go for the gun everytime. I made a heat map to see where the heat is being developed and compared each side with the other (one is alway hotter though). An IR gun can tell you if a single flapper is being a pig or whether the thermostat is being too lazy to open when it should or whether something has been assembled wrongly in that area.

d) You will need to check your boat's arrangements but on mine there is a 2" piece of hard plastic tube that crosses the boundary between outdrive and the engine compartment. It isn't shown on the diagram. The outdrive hose pushes on one side of it and the engine inlet hose goes on the other side. It gets the water through the transom divide. I have had one cracked by a clumsy engineer who tightened up the hose clamps too much. Water from the outdrive was mixing with air. It is also a bit of a waterflow bottleneck as it has a smaller diameter than the hoses because the hoses fit over it.

e) Flappers can jump out of situ and jam shut when the engine exhaust water flows. They reverse their action in effect. They can get mishappen over the years. They aren't difficult to check or change. You just slide the rubber riser gater down the exhaust and out of the way using loads of liquid soap to lubricate it. Sometimes you need to break the dirt seal they make against the exhaust metalic parts.

f) The hose from the Circulation pump to the thermostat housing has wire in it to stop it collapsing. You can see if this is happening and take the hose off to make sure that the wire is ok. This is a sneaky one as it happens out of sight when running the boat hard. You can't be at the helm and watching the hose.

g) The circulation pump can fail in a mysterious way. The impeller inside the pump is an interference fit on its shaft. This gets loose and can fail to turn under load. You can test it once it is off by holding the pully and rotating the impeller by hand. If you can spin the impeller by hand it is shot.

h) Does the overheat correspond to having the outdrive raised? Raising the outdrive will cause the outdrive hose to kink and restrict flow. This is a crucial test following any work that removed the hose.

In the few years that I have had my 2452 I have had all the above issues. Thanks to Rick and others I got through them. Good luck.

Terry

[Guest]

I solved the problem (Edit: Problem is not solved! See follow up post!). I edited my previous post ' removing the thermostat as a test', which was faulty - I put the answer there. Thanks to all who posted!

TerryW wrote:
... here are a few ideas from someone who lost a whole season when a dodgy engineer wrecked his waterflow . . .

Thanks Terry, I appreciate your detailed response. I may refer to it again sometime!

[TerryW]

Well done and happy boating.

Thanks for posting the solution. It will save someone else a whole load of trouble sooner or later.

[Guest]

wildman wrote:
I solved the problem....

No, I didn't. The problem doesnt appear to be the check balls. I had the problem again. I tried expanding the check springs, then removing the check balls. I tried running without the thermostat and the check balls. It continues to overheat at idle. I'm going to create a new post.

[Guest]

continued in thread 72871