Overheats and don’t know why

[pdecker]

I have a 1982 boat with a late model A4, FWC, Vetus Aqualift muffler. Running at 1000 RPM the temp is 185. At 1500 RPM the temp goes to 195, and the Temp light goes on. It’s the same problem I had back in August and I’ve done a lot to fix it, but it’s still a problem. I made it to an anchorage for the night and posting this using my phone.

Back in August it was running hot. Finally I noticed the bilge pump light running and no cooling water coming out the back. I checked the engine compartment and found water gushing out the side of the engine block. After being towed home, I replaced the very rusty side plate with a new one from Moyer, and manually removed a large quantity of gunk filling up the water jacket. I reassembled everything including a new impeller and shaft. The hoses are one year old and the exhaust manifold was ultrasonically cleaned a year ago. I tested the thermostat in a pot of water on the stove and confirmed it cracks open at 165 and is fully open at 175 degrees. I ran the engine at idle for 45 minutes before setting out and it held at about 175 to 180. We noticed that there is less water coming out the back than before the problem and the engine sounds louder. What could it be? Clogged muffler? Thermostat?

[nyvoyager]

I've had great success doing a muriatic flush. I don't recall the specifics but you can sesrch on this site. It is not difficult vut be very careful using muriatic and protect yourself.

[roadnsky]

We noticed that there is less water coming out the back than before the problem and the engine sounds louder. What could it be? Clogged muffler? Thermostat?

It sounds like you definitely have a blockage somewhere.
A quick fix to get you going might be to clamp off the bypass hose for better cooling.
If you don't have a BYPASS VALVE (see pic) then you can use vise grips to clamp off the hose.
Use a rag between the jaws of the vise grips to avoid damaging the hose.

Let us know if this helps...

[joe_db]

A FWC engine should not be having the block clog up repeatedly. Also, is it electrical or mechanical FWC?
EDIT - A poorly done, i.e. no block flushign, FWC conversion will send all kinds of crap to the heat exchanger and clog it up.

[pdecker]

RWC not FWC

My big mistake. My engine is RAW water cooled, not fresh water cooled. I have wet dreams about FWC.

[indigo]

Overheating or Not?

There always seem to be a couple of cases going on at any given time where in an owner has an engine that is overheating. Despite trying all of the normal remedies and proven troubleshooting processes, the situation persists. There may well be an underlying cause that is relatively easy to diagnose though not as easy to remedy.

The temperature sensor on the late-model head resides at the forward end of the head and it relies upon the flow of coolant around it to give a proper indication of engine temperature. One of the primary routes for such coolant is through the forward most oval shaped passage which provides a route for coolant from the block to the head on the manifold side. It has been found that these passages quite often become totally blocked especially on those engines that have been raw water cooled with salt water. If they are blocked, then the flow around the temperature sensor becomes somewhat stagnant causing it to indicate an artificially high temperature where in reality, the cooling system is operating properly.

One means of determining if your engine has this issue is to remove the thermostat, pinch/close off the thermostat bypass hose and then check the temperature of the coolant leaving the manifold with an IR gun or contact thermometer. If the temperature is significantly lower than what the temperature sensor in the head reads, then your engine is very probably suffering from the condition described above.

Another means of determining if your engine has this issue is to relocate the temperature sensor to a location that allows it to "see" all of the flow leaving the head. This can be accomplished by attaching a series of tees and other fittings to the 3/8 NPT connection on the thermostat housing. Such an assembly of fittings is shown in the attached image.

The temperature sensor screws into the first tee on the left where indicated. The bypass hose that normally connects to the thermostat housing now connects to the hose barb fitting at the bottom as indicated. Then the hose barb fitting on the top gets connected to the aft end of the manifold (the Thatch Mod). With this plumbing arrangement you have thus segregated the flow from the head from the bypass flow and the temperature indicated by the relocated sensor is now indicating true engine temperature.

If the suggested temporary test or plumbing modification is implemented and the temperature sensor indicates a significantly lower reading than that which was obtained with the sensor in the traditional head location, then at least the forward most "oval" cooling passage on the manifold side is blocked. This is a situation that should be resolved in order to insure proper cooling of all portions of the block and head. Unfortunately, no amount of acid flushing will clear a totally blocked coolant passage. In order to remedy this loss of coolant flow, the head must be removed and the "oval" passages manually cleaned out in both the head and the block. With regard to the head, it may well be more advantageous, for a host of reasons, to just replace the head with a new MMI head.

Tom Stevens

[joe_db]

My big mistake. My engine is RAW water cooled, not fresh water cooled. I have wet dreams about FWC.

My FWC system is still for sale. HX, thermostat, 2 pumps, and various fittings and hoses. PM me if interested.

[ndutton]

I don't think FWC will solve the immediate problem, actually might make it worse.

Assuming the current temp readings are different than in the past and the pump is pumping to spec, the first thing I'd do is try to get the temp down by removing the stat and blocking the bypass completely. If this does not get the temp down to the 100's I'd suggest an acid flush next (not vinegar but diluted muriatic acid following Don's protocol) and if that doesn't do it, start disassembling and physically clearing out the coolant passages in the block and head. Shortly after reassembly and testing, another acid flush and then install FWC as soon as possible.

[pdecker]

Thanks, all. I removed the thermostat and clamped the bypass hose. Hopefully that will get me the four miles to home today. I have Don’s Service and Overhaul Manual and I will try the acid flushing procedure this week. It has never been done on this engine, and is way overdue of course.

By the way, I think the temperature gauge was probably accurate since steam was coming out the exhaust while the engine was running.

Phil Decker

[indigo]

What did the temperature indication do with your new configuration of coolant flow?

Tom Stevens

[pdecker]

I finally made it home! (I didn't leave until the current was going in the right direction, just in case.) After several hours of running the engine, the temperature according to the temperature gauge crept very slowly up to 180 F after running at 1000 RPM max. I read the temperature of the temperature sensor housing and it was within about 10 degrees.

At the same time, I took the temperature of the fitting on the exit of the manifold with the IR gun and it read 200 F. There is still noticeably less water flow out the back than before the problem started in August.

Next step, I'm going to order the flush kit from Moyer. While waiting for it to come in the mail, I am going to follow some of the fault tree procedures in the Service and Overhaul Manual, namely, test the water flow rate out of the pump with a five gallon bucket. Then test it in other places down the circuit to isolate the blockage.

Poor engine is feeling hot, hot hot. https://youtu.be/HjO6FDCPIzA

Phil

[ndutton]

Good news on making it home

You've got this Phil. Figure out why the water volume is reduced (pump or blockage) and rectify. Because the volume was reduced prior to and following stat removal the usual suspects are pump performance and manifold/fittings blockage. I'm betting on the latter.

edit: the exhaust water injection fitting is a possibility too.

[Nahart]

Raw water cooled here, Had a similar problem

I had a similar heating problem. I did all of the obvious including the acid flush, but still overheating. I then did the flush of the manifold only, as mentioned in the procedure. I flushed both ways in and out of the 2 ports on top of the manifold. I couldn't believe what came out of that manifold. Now, I run cool with no issues.

[pdecker]

Found a clog!

Before doing any flushing, I wanted to take baseline measurements of how much water was coming out of the pump, through the block post-thermostat, and post-manifold. She failed the first test. I measured the flow of water out of the pump into a 2 gallon bucket to be 0.5 GPM. Obviously this was a big part of the problem.

I took the pump apart and attached hoses and ran wire ties through the fittings to free any obstruction. I didn't find any, and the pump seemed to be in good shape. Then I removed the hose from the through-hull fitting valve to the pump and found that the top of the valve was packed with shells. It turns out, there is a reducing fitting between the through-hull valve and the 1/2" hose that leads to the water pump, and it was completely packed up. The photo is attached.

After cleaning and reassembling the pump, I performed the test again and got 2.7 GPM at 1000 RPM. I changed the configuration again to measure the flow out of the thermostat outlet with the thermostat removed and by-pass hose clamped, and got the same measurement of 2.7 GPM. I realize that it is supposed to be 3 - 5 GPM, but there my measurements might be inaccurate since I only have a 2 gallon bucket, my tachometer might be a little off, and the bucket was in the cockpit instead of the cabin which would cause two feet of head loss. But the water flow seems much better. After putting it all back together, it looks like normal flow is coming out the back of the boat. I'm still going to do the flush this weekend.

[sastanley]

Great photo and update. 2.7 is way better than 0.5!!!