Overheating and a question about heat exchanger flow

pschauss · Post by **pschauss** » Oct 6th, '22, 18:52

My engines (454's) were running well through the middle of August. When I took the boat out in mid-September, the starboard engine started to overheat, with the temperature gauge showing almost 200. After I cleaned the strainers (Grocos) I thought that I saw a slight improvement, that engine still ran over 190.

I replaced the impeller on the raw water pump but did not see an improvement.

I am suspecting that the problem is on the raw water side of the system because the risers are too hot to touch, considerably hotter than on the port engine.

I replaced the risers last spring, so I cannot imagine that the two on the starboard engine could have gone bad so quickly and so suddenly.

One possible clue is that the seawater no longer drains out of the starboard heat exchanger after I shut down the engine, as it did before (and as it does on the port engine).

I took both end caps off of the heat exchanger and sprayed water through it. There did not seem to be any blockage.

Finally, I am a bit puzzled about how the heat exchangers work. I notice that the raw water flows in through the bottom left end of the tank (as you look at it from the rear of the boat). The raw water output to the risers is at the top left of the tank. Since water flows in and out on the same side, what is forcing water to flow over the matrix in the middle?

scenarioL113 · Post by **scenarioL113** » Oct 6th, '22, 22:56

Is there a possibility that your water is being restricted from entering the system? Like the thruhull has some kind of a restriction? Whether it be barnacles or other debris. I had a bad valve that was closing on itself a few yrs back (a guillotine gate-type valve). The vibrations was causing it to close...

How is the flow out the exhaust?

Does the problem happen only when cruising? but cools off when you throttle back???

pschauss · Post by **pschauss** » Oct 7th, '22, 05:48

I am getting a good flow through the sea cock.

The water temperature drops when slow down to about 2500 rpm.

Carl · Post by **Carl** » Oct 7th, '22, 06:48

The way I have understood marine cooling, is the cooling system is JUST adequate. So a 10% blockage reduces your cooling by 10%. The more the engine works the more cooling it needs so running at cruise it needs full flow to properly cool.

That said we have to make sure raw water intake is fully open, the strainer is not clogged, and hoses are not kinked or old with insides deteriorated. I like to squeeze 'em...shouldn't be soft or hard n crunchy.

When you replaced the impellor...did it have all the vanes intact? If not they went someplace, usually the first place is the trans cooler. Pull hose and check for debris, that vane needs to be found if it was missing.

Spraying water through the heat exchanger and seeing coming out the other side can mean everything or very little. IF you saw water come out of every tube, great. But was it coming out all of them? Several clogged tubes will reduce the flow and your motor cooling. I'd consider rodding all the tubes to be sure.

After the heat exchanger, the water goes into the riser or the exhaust manifold? If the manifold they need to be checked.
If out the riser check the hoses and fittings.

Your exchanger sounds like it has two chambers. Raw water goes in on the bottom half, runs to the right, goes up and back to the left side on top. The left side should have a plate dividing top and bottom with end cap sealing it.

Dumb question...how the belt driving the raw water pump? Is it snug enough? Could it be slipping?

When running I like to feel the hoses, especially the ones feeding the risers...compare sides they should be similar. I've disconnected to compare flow. Obviously not for very long and dockside goosing the motor a bit. Bad flow can be seen....a little off is difficult.

When running, compare the flow from the transom...same flow or ones a bit less?

Tony Meola · Post by **Tony Meola** » Oct 7th, '22, 23:18

Peter

I had the same issue with my Cummins. I found the heat exchanger was clogged. Almost the same symptoms as you. I had eel grass and zinc clogging it up.

That fixed the problem short term. Then it started again, but everything was clean turned out to be a bad thermostat. Was not opening all the way or sometimes it would open, then close again.

Check the flow of water coming out the exhaust while running. Sometimes if you have a clog it will reduce the flow.

The heat exchanger has copper tubes that the fresh water/ anti freeze flowers through. The sea water pump Bush's sea water through y yhe heat exchanger and as the sea water flows over the copper tubes it cools down the engine water.

pschauss · Post by **pschauss** » Oct 8th, '22, 09:56

I pulled the raw water pump for the second time and replaced the impeller with the official Jabsco part. I had been using an impeller from a Mercruiser plastic-bodied pump which looks like it is about the same size as the Jabsco. It turns out, however that the Jabsco part has 10 blades where the Mercruiser part has only 8.

I also removed and flushed out the transmission oil cooler. I did not see any indication that it was clogged.

I let her idle at the dock until the upper tank on the heat exchanger started to get warm, telling me that the thermostat had opened. I could see that I was getting a good flow of water out of the exhaust. Subjectively, it looked better than with the 8 bladed impeller. The risers stayed cool to the touch.

I went out for a bay test. Running at 3000 rpm, my starboard engine went up to 190+ and looked like it was going to keep going up. Risers were hot to the touch, about the same temperature as the manifold which is freshwater cooled.

I came back at 2000 rpm and the engine temperature dropped to about 160-180. Back at the dock, with the engine idling, the risers were stone cold.

Tony Meola · Post by **Tony Meola** » Oct 9th, '22, 00:03

Peter

Water flow at idle may look normal. It's at speed that a difference will show up if you have a restriction.

pschauss · Post by **pschauss** » Oct 22nd, '22, 10:12

I took my raw water pump out again (Jabsco 43210) and replaced the cam, wear plate, and impeller. The old impeller showed no signs of wear or missing pieces. I also took out the transmission oil cooler and flushed it out with fresh water. Holding it up to the light I could not see anything blocking it.

I took the heat exchanger to a radiator shop and had it boiled out. They said that it was pretty badly clogged and left it to soak an extra day to get it completely cleaned out. After I reconnected it, but before I reinstalled the raw water pump, I connected a hose to the upper seawater outlet and poured in about a gallon of water. The water came out quickly through the transmission oil cooler, so I know that there is no blockage in the heat exchanger or between it and the raw water pump.

Once again, here is what I am seeing:

- Risers stay cool idling at the dock.
- As soon as I get up to about 2500 rpm in the bay, the engine temperature starts to go up. Risers get very hot.
- When I drop down to 1000 rpm, the engine temperature starts to drop, and the risers cool down quickly. By the time I get back to the dock the risers have cooled off completely.
- If I disconnect the seawater output hose from the heat exchanger, idling at the dock, I get a good flow of water.
- My starboard engine has always run about 10 degrees hotter than my port engine and I have always seen steam coming out of the exhaust.
- My starboard engine has a Jabsco bronze bodied raw water pump. My port engine has the Mercruiser or Sierra pump with the plastic body.

Is it possible that my Jabsco raw water pump is worn in some way that it loses efficiency at higher speeds? From what I have read, these pumps are reputed to be more durable than the Mercruisers or Sierras.

Carl · Post by **Carl** » Oct 22nd, '22, 13:28

A pump may not lose efficiency but it may only be capable of pumping so much water because…

Having twins can be an awesome advantage. Can you swap pumps and if problem follows you have your answer on the pump.

scenarioL113 · Post by **scenarioL113** » Oct 22nd, '22, 15:59

Keep digging, there is def a prob in the raw water side...the risers should not get hot to the touch like that.

Maybe you have an "air" leak and sucking air into the system and causing a cavitation in the raw water and not getting good flow when you are revving at your cruise RPMs and higher.

Do you have the glass strainers?

It would be an odd-ball problem but you never know...

I agree with Carl and say swap pumps from side to side

You could also try and swap intake hoses from engine to engine to rule out a restriction on the thruhull or the strainer

Stephan · Post by **Stephan** » Oct 22nd, '22, 17:50

This is frustrating.
Given your recently cleaned heat exchanger and the experience I have had with the transmission/oil coolers I might focus there. I have gotten used to feeling the pressure of the hoses feeding the transmission/oil coolers and the ones running across the top of the engine to the heat exchanger. I have a slight amount of back pressure in the hoses on the inlet side of the transmission/oil coolers. I have had zincs swell up and shed scales in the transmission/oil coolers.
Regarding your question about flow in the heat exchangers, I believe there is a block-off plate in the end of my heat exchanger where the raw water comes in. This forces the raw water to run the length of the heat exchanges and then make a u-turn at the opposite end. I think this picture shows how only about a 1/3rd of this heat exchanger is open.

You wouldn't be the first to cut a circle of plexiglass/lexan to make a temporary end cap to see the flow through your heat exchanger...
Good luck,
Stephan

Carl · Post by **Carl** » Oct 22nd, '22, 21:56

Frank brought up another good point, hose connection. Old hoses get crusty and may not seal to the fittings no matter how tight the clamps. But I think you mentioned they are new….

How about the fitting surface… is it clean or scared from pliers, corrosion or a hack saw? I’ve had fittings crushed oval that did not seal. All it takes is a tad bid of air sucked on the incoming side and your motor will not get all the water it needs.

Tony Meola · Post by **Tony Meola** » Oct 23rd, '22, 20:25

Peter

Still hot after the heat exchanger has been cleaned out. UGH!. Switch pumps as recommended. If you still have the problem, try running barnacle buster throught he system. If anything is scaled up that you are not seeing that should clean it out.

Carl · Post by **Carl** » Oct 24th, '22, 06:46

Another thing mentioned is you changed the impellor, wear plate and cam....but how did the rest of the pump housing look? If heavily worn the pump will not pump efficiently as water is skirting between impellor and housing, this means your pump never gets to the maximum flow, which usually means not enough water to cool motor and exhaust when needed most, at Higher RPM's.

Which also brings me to is the pump sealed correctly? Are mating surfaces clean, using the right gasket or o-ring? Cover secured right? If the pump sucks air it won't be pulling enough water...same goes for the hoses and connections before the pump.

Rawleigh · Post by **Rawleigh** » Oct 24th, '22, 15:49

Also you could have an aneurysm on the inside of one of your hoses that doesn't open to restrict the flow until you are running hard. A delamination on the inside of a hose could cause your problem.

pschauss · Post by **pschauss** » Oct 26th, '22, 14:50

Thanks for all of your suggestions.

I pulled the hose off of the sea cock and the flow is definitely restricted so I must have a blocked external strainer.

Tony Meola · Post by **Tony Meola** » Oct 26th, '22, 21:57

Peter

Could be a plastic bag. Try back flushing it with a hose.

Carl · Post by **Carl** » Oct 27th, '22, 07:07

LOL...Even the best of us forget or just flat-out bypass the first and most obvious steps at times.

For overheating ... the place to start is checking the inflow of raw water, starting at the intake strainer, and verifying the Sea Cock is open "ALL The Way"...guess who forgot that part for a good part of a season. In my defense...which is a lousy one, I did check that the wrench handle was in line with the flow. BUT I assumed the wrench was in line with the opening in sea cock. It was not.

pschauss · Post by **pschauss** » Oct 27th, '22, 17:14

The caps on my Groco strainers are so close to the water line that you can’t get much of an idea of the water flow through the sea cock. The hose from the sea cock to the strainer is very short and it took me about an hour to get both ends loose from the barbs. This, the reason that this was the last place that I checked.

pschauss · Post by **pschauss** » Oct 27th, '22, 17:14

The caps on my Groco strainers are so close to the water line that you can’t get much of an idea of the water flow through the sea cock. The hose from the sea cock to the strainer is very short and it took me about an hour to get both ends loose from the barbs. This, the reason that this was the last place that I checked.

Rawleigh · Post by **Rawleigh** » Nov 1st, '22, 11:23

Do yourself a favor and get a Lisle 80290 Hose Removal tool. Hose removal is so much easier! You can run it around inside the hose to unstick it and then use it to help pull the hose free!

pschauss · Post by **pschauss** » Nov 1st, '22, 12:22

I have two of them, one with a sharp bend in the hook and one with a right angle bend. I used both of them.

Carl · Post by **Carl** » Nov 2nd, '22, 06:11

pschauss wrote: ↑Oct 26th, '22, 14:50 Thanks for all of your suggestions.

I pulled the hose off of the sea cock and the flow is definitely restricted so I must have a blocked external strainer.

So after you backflushed or cleaned out strainer how'd your temps go?

pschauss · Post by **pschauss** » Nov 2nd, '22, 06:59

I had her hauled for the session last Friday. When they washed the bottom they scraped a lot of barnacles off of the strainers. From the looking at the barnacle scars on them I don’t think backwashing would have cleared them.

I plan to remove them to clean out whatever is behind them. Depending on what I find, I may want to replace them with something that I can clean out more easily.

Here is what the starboard strainer looked like after they scraped and washed the bottom:

http://www.ipernity.com/doc/307687/51652454

Stephan · Post by **Stephan** » Nov 2nd, '22, 11:11

Oof!
Those Barnacles got in there good. Your strainer looks to be more restrictive than the ones I'm familiar with.
I have had luck propping up a neoprene lined board to block the intake and pouring a high concentration of Muriatic Acid/water into the intake from inside the boat. After letting it sit for a few minutes I flush with fresh water and baking soda solution to neutralize. I can't see from the picture, but my experience has been that barnacles grow on the inside of the strainer as well when they are that developed outside.
Good luck,
Stephan

scenarioL113 · Post by **scenarioL113** » Nov 2nd, '22, 19:38

Every one of those strainer holes are restricted from not just barnacles but from encrustation. I would ream every single one of those holes and maybe even increase to the next size up drill bit. I did it on mine last year.

Not much you can do about growth on the inside tho except pull them off every few years I guess and clean them.

pschauss · Post by **pschauss** » Nov 3rd, '22, 07:31

I’m thinking of replacing these strainers with one like the Groco ASC-1250 which has an access door so that I can clean it out.

Any thoughts?

Carl · Post by **Carl** » Nov 3rd, '22, 10:03

I have two thoughts...maybe more.

The strainers with the removable screens are nice as you can open them to verify nothing is in there instead of pulling the whole thing off to check. Something that can also be checked in the water if your one to play under the boat...and not one to drop a screw or wrench.

Last time I removed my solid strainer was...maybe 15 years ago, perhaps longer, nothing to speak of back there as I recall. I did however do what Frank said and that is open the holes a size or two as I "felt" the outside growth was inhibiting flow, kinda like yours with holes shrinking due to growth. The motor did run cooler after enlarging the holes, but I felt better.

This brings me to, unless you check and clean the front and back of the strainer, and then test Run the boat, you do not know if you corrected the problem.

FYI- after I had pulled my strainer and realized nothing was back there years ago...I now just go in with a small rod and poke around to see if I feel anything every now and then. I haven't, so left them up without pulling to check.

Rawleigh · Post by **Rawleigh** » Nov 3rd, '22, 11:54

Oysters and barnacles will grow in the intake thru hull here, so being able to open them is a must! The screens can also be unbolted and sandblasted.

Amberjack · Post by **Amberjack** » Nov 3rd, '22, 16:30

pschauss wrote: ↑Nov 3rd, '22, 07:31 I’m thinking of replacing these strainers with one like the Groco ASC-1250 which has an access door so that I can clean it out.

Any thoughts?

Peter-I replaced my Groco internal strainers with Groco external strainers in 2017 and they have performed well, i.e. I hardly pay any attention to them. Mine were APHS 3000-2 which is the screen version instead of slotted. Screen vs slotted depends on local conditions. They are very easy to open and clean but I have never needed to.

The 3000's are 15.4" x 6" which may be oversized but like anchors I went up a size to be comfortable. Captain Patrick posted instructions on how to install them which I followed carefully. He may have included sizing recommendations.

Tony Meola · Post by **Tony Meola** » Nov 3rd, '22, 20:57

Peter

What did you paint them with? Bottom paint or the zinc spray?

When I had those same strainers, we use to pull them down each year, and paint inside and outside of them then clean the paint out of all the holes that closed up from paint. Never had an issue in doing that. Ours installed with machine screws and nuts on the inside of the hull, so it was a matter of removing the nuts and dropping them. Caulk when putting back up.

If I was installing them today, I would go with the new ones that have a removable or a screen you can open and clean and paint the inside.

pschauss · Post by **pschauss** » Nov 14th, '22, 21:54

Here is what the inside of my starboard strainer looks like. My port side strainer wasn't quite as bad.

http://www.ipernity.com/doc/307687/51669832

Tony Meola · Post by **Tony Meola** » Nov 14th, '22, 22:39

Peter

I have seen worse on the inside. But your prior picture of the external area shows that there was probably enough to restrict water flow. I am assuming the power washing and scraping removed some of the growth.

Personally if you are using ablative paint, I would purchase a quart of the Hard non ablative paint and use it on your metal especially if the boat sits for a few weeks. I find that the ablative paint does not always last on the underwater gear.

pschauss · Post by **pschauss** » Nov 18th, '22, 13:21

When I removed my strainers, I found these scoops underneath.

http://www.ipernity.com/doc/307687/51674376

Do these serve any purpose I install an external strainer like the one shown below?

https://www.generalpropeller.com/00RSS1000P

Thanks,

Carl · Post by **Carl** » Nov 18th, '22, 22:30

That is the original raw water intake strainer. More than just a cover as it goes thru hull and locked in place on the inside with seacock or large flanged nut with valve screwed on top.

https://www.homedepot.com/p/Perko-Intak ... 51#overlay

pschauss · Post by **pschauss** » Apr 16th, '23, 08:40

I replaced my Great South Bay strainers with a pair of Buck Algonquin strainers with removable screens.

The yard put my boat in on Wednesday. Based on a 30 minute run from the yard to my slip, it looks like the overheating problem has been solved.

Over the winter I also had the yard bead-blast 40+ years of bottom paint off of my hull. They patched the blisters and applied four coats of barrier paint. My cruising speed on the way over to my slip was 24 knots at 3000 rpm. Previously, the best I ever got was 23 under ideal conditions.

Carl · Post by **Carl** » Apr 16th, '23, 12:05

Sounds like a good start to your season.

Also sounds like you had a whole lotta paint on the bottom

Enjoy!

Tony Meola · Post by **Tony Meola** » Apr 16th, '23, 23:18

24 knots with big blocks is pretty good.

Glad to hear your problem is solved.

Snipe · Post by **Snipe** » Apr 17th, '23, 05:40

My boat with the 454 crusaders ran 24/25 knots at 3000. Glad you got it sorted out. Hopefully one day we can all get together soon.