Overheating Issue

[hanleyclifford]

I don't like the sound of that. Should I even try the muriatic acid flush?

It isn't good news and I see that Neil concurs with the diagnosis. However, since you are facing a removal of the head anyway you have nothing to lose by following John's procedure regarding the temp sender. The outside possibility is that you might jar enough junk loose to give the acid a shot at clearing the rest of the blockage. You will need maximum available pressure so clamp the by pass and give it a shot. If you get cleared as far as the sender, do the acid and maybe breakup some junk further downstream. If this fails you will have to pull the head and do the cleaning mechanically. Actually, though, if you are laid up for the season this is a good excuse for a look-see under that cylinder head. Just sayin'.

[Marian Claire]

BlueWhale. Thanks for the additional info. That clears things up for me. I asked about a possible grounding because often mud and other crud can be pulled in thru the raw water intake as we gun the engine in an effort to get to deeper water. DAHIKT.
Dan S/V Marian Claire

[Mo]

I ran across a similar issue a few years back helping a friend with a Yanmar 2gm diesel. We let go the pump and blew compressed air back through the block and rust scale came out inlet where the pump line went on...that was the end of his issues. We figured scale would move and cause a blockage. I don't think the Yanmar has the metallurgic composition of the A4 and might rust prematurely.... Not sure at all if that would be a viable option or issue for the A4. At the time we did that we'd tried everything we could think of to clear it. It would be fine at idle and as soon as it worked it would heat up.

[Marian Claire]

Has the cap been checked as a possible point of blockage?
Reason I ask is the block and head have multiple openings and passage ways. All of them would have to be clogged for there to be zero flow out the exhaust after the T-stat closes the bypass. I was amazed at how blocked my passages were when I rebuilt my A-4. But even as bad as they were I never overheated.
The cap or the T to the cap seems to be the one place that if blocked would shut down the whole flow.
Just something to look if you haven't already.
Dan S/V Marian Claire

[JOHN COOKSON]

If you have trouble breaking the temp sending unit (or head nuts or exhaust flange bolts) try this:
Shoot the area up with PB blaster or your favorite goop for a few days.*
Start the engine and run it until it is up to operating temp. Brian, in your case be careful not to overheat and ruin the engine or exhaust system.
While the engine is running and hot lay a closed end wrench on it. A 6 sided box end wrench would be a good choice of tools. Tap on the wrench gently to firmly until the sending unit breaks loose. No pounding. You'll only break something pounding on it with a hammer. The engine heat + engine vibration + shock from pounding on the wrench will break the sending unit loose.
Once the sending unit is broken loose turn the engine off and finish removing it.
*I don't like the idea of using PB blaster on exhaust flange bolts on anything that gets real hot. It cooks off and what is left acts as a thread lock.

TRUE GRIT

[BadaBing]

Another alt for back flushing.

Remove the T stat
Seal off the inlet hose barn on the T stat fitting with a bolt and a short pc of hose
Disconnect the hose going from the pump to the T fitting at the water jacket cover.
Seal off the second hose connected to the T fitting that went to the T stat.
In essence you have made it so that water can ONLY flow.through the block from the water jacket fitting to the out flow.of the t stat housing.

Attach a garden hose to the out flow or discharge connection or the t stat housing. Put the hose from the t fitting at the water jacket cover in a bucket., you want to capture the crud that may come.out

Now.be careful! A typical garden hose will produce 20 - 40 lbs of water pressure. Your engine CANNOT withstand that much pressure.

Place a small ball valve fitting, available at any hardware store, into the garden hose connection just before the engine so you can quickly make flow adjustments.

Turn the water on just a little. ( not.a.bad idea to play With the available.flow.prior to attaching to the engine so you have feel for about 1/4 available flow)

If you can not push water through the block backwards, from t stat to t fitting at water.jacket cover, with 1/4 house pressure your not.going to do so with more pressure. Trying too much pressure and flow WILL trash the engine.( It might not but better to assume it will)

If you get some.water flow, even just a little, let it run for a while, the longer the better. Then reverse the hoses and pump 1/4 possible line flow through the engine in the normal direction. Remember to capture the outflow of water out of the engine in both directions. It may tell you a lot by the type of crud it deposits in the bucket.

Disclaimer. If the head ports.are.clogged all the flushing in the world.is not.going to open them up. The water is going.to take.the path of least resistance. However, if a passage is restricted, flushing MAY break loose some of the crud and open things up enough to make an acid flush usefull.

Normally opening the water jacket cover will allow for a good cleaning with picks and shovels. (Awl , spoon anything you can greet in there to scrape it out)l have seen some of the pictures on this forum showing cruddy vs. Cleaned out water jackets?

[BlueWhale]

Well, it seems that "All is Lost" and head removal is the next step. I tried the flush removing the heat sending unit to no avail. I'm located in Baltimore, MD and am still in the water. I don't have great access to the engine and am not looking forward to this task. Thanks for all the advice and walking me through the "easy" fixes.

Brian

S/V Rekofa, The Blue Whale
C&C 34, 1979

[BlueWhale]

Well, it seems that "All is Lost" and head removal is the next step. I tried the flush removing the heat sending unit to no avail. I'm located in Baltimore, MD and am still in the water. I don't have great access to the engine and am not looking forward to this task. Thanks for all the advice and walking me through the "easy" fixes.

Brian

S/V Rekofa, The Blue Whale
C&C 34, 1979

Hold that thought. I neglected to open the through hull valve, DUH. Running the ending produced a good flow to the bilge. Fingers crossed for re-installing the heat sensor.

Brian

[BlueWhale]

Ok, now "All is Lost" 😔. The flush did not get out enuf gunk. Question, if I do the muriatic acid flush and it does not work, will the muriatic acid left in the engine remain there and cause damage? In other words given the blockage will the flush go through the system?

Brian

[Marian Claire]

You can always use vinegar with no fear of damage.
Dan S/V Marian Claire

[Mo]

Ok, now "All is Lost" ��. The flush did not get out enuf gunk. Question, if I do the muriatic acid flush and it does not work, will the muriatic acid left in the engine remain there and cause damage? In other words given the blockage will the flush go through the system?

Brian

As long as you have flow at some point you can dilute the acid. I do muriatic acid flush every couple to three years....you are doing a flush (I mix mine 50/50) and leave it in for 15-20 minutes....it's not going to hurt anything that is not already rusted through....if you want, do a test on a rusty piece of metal in a bucket. If some passage is that rusty best you find out now...do the test and you'll see it isn't that dramatic. I pushed stronger draino into peoples arteries

...anyway, you have flow before it heats up so draw the muriatic acid in...shut down for a bit then fire it up and run 5 gallons of water through...the acid will dilute. Throw some food coloring in your muriatic acid if you need to know how much to draw in...lets say you use blue, at about 3/4 gallon drop from your suction bucket you should see it spit blue out the transom. Once you see that allow it to sit, have a beer or two, in peace and then start it up under normal conditions using fresh water from your bucket. One start up you will see dark brown and maybe a bit of black...normal...might even see some crud come out...normal.

PS: I seem to remember a similar situation, perhaps it was on this forum. Water flow at low idle, and decrease water flow, temp increase with rpm increase. The T-stat removed, and exhaust manifold fitting was checked, later to be found out that a rust scale inside the manifold would work it's way up under the increased flow and block the exit....muriatic flush might help with that as well. Once water pressure built in the manifold it floated up the flake of rust and blocked the exit. If it's a crustacean in the block there causing the issue, I imagine it would be coming out the exhaust. The other thing to consider, I believe it was mentioned, is buildup up of deposits after operating at higher temps for long periods of time...stalactites, in a manner of speaking.

[JOHN COOKSON]

Running the ending produced a good flow to the bilge. Fingers crossed for re-installing the heat sensor.
Brian

It sounds like you are getting good or at least some flow through the engine.

Please do a couple of things before you pull the head.
REMOVE THE THERMOSTAT.
Then put the housing back on, and attach a hose to the output barb and see if you get good water flow. Keep disconnecting cooling system hoses and starring the engine then reconnect the hose and move on down the cooling system in this manner to the back of the boat until you get no flow then you will have the clog localized.

I know this idea flys in the face of a lot of theories presented so far but it would be a bummer to pull the head and still have the overheating problem after you reinstall it so be sure there is free flow in the the entire engine, manifold, exhaust system first.

TRUE GRIT

[Mo]

It sounds like you are getting good or at least some flow through the engine.

Please do a couple of things before you pull the head.
REMOVE THE THERMOSTAT.
Then put the housing back on, and attach a hose to the output barb and see if you get good water flow. Keep disconnecting cooling system hoses and starring the engine then reconnect the hose and move on down the cooling system in this manner to the back of the boat until you get no flow then you will have the clog localized.

I know this idea flys in the face of a lot of theories presented so far but it would be a bummer to pull the head and still have the overheating problem after you reinstall it so be sure there is free flow in the the entire engine, manifold, exhaust system first.

TRUE GRIT

I agree, T-stat out and reassemble without it. Also check that your by-valve is actually working and just open it 1/2. Do the flush in this mode and lets see where it gets you. My tiny little mind tells me it's either T-stat, manifold, or something in an elbow. If it't a buildup of rubber the muriatic acid won't help. If it's organic the muriatic acid will dissolve it an send it out the exhaust. The ones that I've noted, with initial water flow, that decreased as it warmed up were all T-stat issues. No flow or decrease flow on rpm increase sometimes, intake restriction, pump, debris after pump related.

[BlueWhale]

I agree, T-stat out and reassemble without it. Also check that your by-valve is actually working and just open it 1/2. Do the flush in this mode and lets see where it gets you. My tiny little mind tells me it's either T-stat, manifold, or something in an elbow. If it't a buildup of rubber the muriatic acid won't help. If it's organic the muriatic acid will dissolve it an send it out the exhaust. The ones that I've noted, with initial water flow, that decreased as it warmed up were all T-stat issues. No flow or decrease flow on rpm increase sometimes, intake restriction, pump, debris after pump related.

I am a bit confused. When I remove the tstat I assume I should keep the bypass hose clamped off? Since I don't have a bypass valve should I partially clamp off the bypass hose? If I understand the water flow correctly, with the bypass clamped off won't the flush go to the engine by way of the water jacket? If that is the case then the acid won't have anywhere to go as indicated by the tests done thus far? I'm going to try this. I just don't understand how the acid flush will pass through the blockage. I'll try almost anything to avoid removing the head.

It's suppose to get cold over the next couple of days but I think I'll endure it and give it a try.

Thanks.

Brian

[romantic comedy]

I think you would have a valve on the by pass. You can adjust the temperature that way.