Coolant Overflow Reservoir - E38

While servicing my engine this week I got to looking closely at the coolant overflow reservoir. This has always been empty and I assumed it was for expansion should the engine overheat. I keep the water level at the manifold just below the lip at the cap.

The cap on this bottle is a make shift item from the PO and the mount is not secure. In trying to locate a suitable replacement tank I found that this tank is from JC Whitney and apparently not OEM to the boat.

So, my question is does this item appear on other Ericsons and is it really necessary. If it is a beneficial item how do others utilize it? I have heard some say to fill the reservoir to the marked point and use it as a pre-start checklist item to see that you have adequate coolant. I would think that checking at the engine cap would be better, but wouldn't the coolant then overflow while the cap is off the engine?

Any thoughts?

The expansion tank is usually mounted at about the top point of the water passages in the engine, and it is correct to generally have them about half full. Filled properly, the expansion tank is an active device through the normal operating cycle of running cold and warming up to normal operating temperature. It allows for the natural expansion of coolant as the engine comes up to operating temperature without exceeding the capacity of the heat exchanger and water passages of the cooling system and overflowing. Likewise, as the engine cools back down, coolant can be drawn back ensuring that the engine has the proper level for the next operating cycle.

The particular brand of the tank is really not that important. The cap should keep it from spilling, but doesn't need to be special. It should allow for pressure relief in an overheating situation.

My coolant level is kept about 3/4" below the cap. The overflow is stowed next to the #1 house bank (outside the engine compartment) and consists of the hose stuck into the top of a gallon orange juice jug and all that stuck into a large ziplock bag.

Not recommending this, but that's what I found on my 38. I've never had any coolant overflow into it.

The coolant overflow bottle is a nice feature and is pretty much required on higher HP diesels.
The cap on the H/E should be a double acting cap (2 rubber seals inside, 1 for maintaining pressure and 1 for maintaining vacuum). The overflow bottle is unpressurized and the only requirement is that coolant always covers the hose fitting so no air can enter the cooling system. The H/E needs to be totaly full when the engine is cold and then the overflow bottle is filled +/- 50%. This will keep all air out of the cooling system when the engine thermal cycles during running. By the way, the location of the bottle is not critical. It can be above the engine or along side of it, as long as the H/E cap is proper and in good shape.

Thanks guys

That all makes sense. The present cap on the reservoir is a loose fit, and the tank bracket does not securely hold the tank with the weight of fluid. I will get a new tank and use it. The existing tank would just fall over and empty into the trash bin, locker, and engine well on a port tack.

The tank is mounted above and to port of the trash bin in the cockpit locker. When I added fluid to the tank it did not gravity feed to the engine with the H/E cap in place. Perhaps the cap allows that flow when temperature requires. I will top off the fluid level in the H/E and the expansion next time I run the engine should purge any remaining air. I will also need to trace the rubber tubing and look for kinks and binds.

Craig, this tank is $10 at JC Whitney if you want to change your set up.

I appreciate the help.

My cap to the overflow bottle has a small vent hole in it so air can move in and out as the volume changes with temperature... I don't think that the overflow system should be air-tight.

Mike

Heres a funny one: When I got my E38 it had coolant overflow bottle installed. The level never changed, at least I never saw it move off the "cold" mark. I flushed the coolant after the first season, topped off the engine at the pressure cap, and all was well. Then I noticed a bit of coolant seepage at the overflow hose right by the pressure cap on the engine. Hmmm, strange. I removed the overflow bottle, and in the process of removing it, pulling the hose off the bottom of the bottle, no coolant came out! A manufacturing defect had completely occluded the plastic hose nipple! So for however long that setup was installed the overflow bottle was a decoration. I drilled out the plastic nipple and all is well now, the system functions as intended. Word of caution, check and make sure any bottle, installed or otherwise actually flows coolant. RT

"While servicing my engine this week I got to looking closely at the coolant overflow reservoir. This has always been empty and I assumed it was for expansion should the engine overheat. I keep the water level at the manifold just below the lip at the cap."

I'm wondering why is the coolant recovery bottle always empty? I'd pour some liquid in the bottle and then check the bottle, hose and hose bib on the heat exchanger for leaks, just in case.

Actually Harvey, it was empty because I never put any fluid in. It was empty when I acquired the boat and I assumed it was just for overflow. It has fluid now and is holding it's level. Thanks to the above posts I will replace the tank with one with a secure cap and better mount, then use it as described by Gary and David. Perhaps eliminating air in the system will help the engine run cooler. It tends to run hot at higher RPMs.

Bill,
My engine ran hot at the upper RPM ranges until I replumbed the hot water tank the correct way and I also installed the current new raw water pump made by Sherwood. I also had an issue when the engine electric temp gage would start rising up to dangerous levels and a NEW temperature sending unit corrected that.
Remember not to have too much antifreeze in the cooling system. 30/70 is about the max to use. Straight water will lower engine temp about 10-15 degrees F by itself.

Sherwood Pump

Thanks Gary.

I re-plumbed the water heater two years ago and it helped. Last weekend I cleaned the heat exchanger (again), and found some zinc residue that may have restricted flow some. It may be wishful thinking, but it seems like there is greater flow at the exhaust. I am focusing on the prop next. There is a very expensive Autoprop on the boat. It is a complex prop and perhaps even light fouling may adversely affect performance. I have asked the diver to pay particular attention to it and the raw water thru hull on the cleaning scheduled for this week.

I have heard that the newer Sherwood pumps have greater flow rates than the Oberdorfer I have now. I will consider the change. Is it pretty much a bolt exchange?

Bill,
Yes the Sherwood is a straight exchange. Make sure you get the complete kit as there is an adaptor plate that bolts to the engine cover first. Don't overlook the electric temperature sending unit. Mine was going "whacko" and was reading erracticaly (sp). You can test the accuracy with an infra red temperature gun. Being in Florida's warm water doesn't help much either!!

Gary,
I have been considering an IR temp sensor for this and other applications, so I might just give one a try. A new temp sending unit would probably cost about the same, so perhaps I should just get the sending unit and be done with it.

I have not looked at the pumps in quite a while. Last time I was looking at Torresen Marine. Got any better suggestions. It would be nice to not spend any more than necessary. Is it the only pump available or is it possible to get the older one in error?

Hi Bill,

I have heard good things about the folks at Depco. Here's a link:

http://www.depcopump.com/

Depco

Thanks David,
These folks are fairly close to where I keep the boat so I might drop by and talk with them. I will also look into the Moyer Marine replacement pump. Being able to use the several spare impellers I still have would be a plus. They are not cheap.

How did the cockpit table work out? Did you get it refinished?

Hi Bill,

Things got delayed due to a war with my binnacle followed by a mishap with the pedestal guard, which in the long run has worked out to be a good thing. I'm just finishing it up, if you can believe it. I messed around with the binnacle on and off throughout last season soaking with PB Blaster and working with an impact driver to no-avail. This spring I decided to get brutal, and got out the torch and went to town with a 5 lb hammer and impact driver and several packs of driver bits and finally got the brute apart without breaking anything I didn't want to break. Picture of one of the screws after removal below. Next, I did a test run of just the guard in place, but I had not secured the base to the cockpit sole as I wanted to do a sail making sure there wasn't a foot space issue in the cockpit. Heeled over nicely and my friend looses his balance, grabs the guard and torques it and snap goes the end. OK, what to do - it's cast aluminum. Luckily, we've got a nice little metal working shop here in Annapolis (for locals, it's Metalcraft Engineering), and John and I chatted out a few ideas, he did a test weld, and I think it's now better than new. As you can see below, we decided to weld tubing on to both sides. The guard is now completely done and installed properly So, after all this, I have a teak wheel I'm refinishing, and the table and wheel are being done together right now as a joint varnish project. Of note, when my wife went for her first sail with the guard installed, she reached out and grabbed it reflexively, and with a big smile, said she really liked this upgrade to Emerald. I think you get credit for perhaps coming up with the one thing that's gotten more applaud than anything else I've done on the boat! Can't thank you enough for that!

Sure feels good when these things are done, doesn't it?

Bill