Need help getting an air gap out of the coolant system on Univesal Diesel engine

[sailinggreg]

Hi All,

I've got a Universal Atomic Diesel model 5416 on my 1980 Erickson 30+ sailboat. I believe I've got an air gap in the coolant system.

Just replaced the heat exchanger because there was almost no seawater coming out the back. A couple years ago had the heat exchanger insides cleaned out, so seemed like it was time to replace it. A boat buddy guided me and I connected all the hoses. I refilled the coolant, started the engine and have great water coming out the back.

Unfortunately, after the engine runs about 12-15 minutes and the engine warms up, the temperature gauge then quickly goes all the way to maximum. I've run the engine at the dock three times now with the same result.

Fyi, this boat has three places where it is possible to add coolant; 1/ on the engine, 2/ in a metal reservoir and 3/ in a plastic reservoir. I'm told boats have the metal reservoir when there's a hot water tank that's higher than the engine, which is the case with my boat.

My method for filling the coolant was to fill at the engine first, then to the metal reservoir and then the plastic reservoir. After I ran the engine the first time and the temp gauge went to maximum, after letting it all cool down, I checked and was able to add more coolant in the metal reservoir. So it had drawn down coolant. Can't add more coolant directly to the engine because, since its lower than the reservoir(s), as soon as you start to open that cap coolant spills out.

I was told by a mechanic that Universal diesel engines have a plug to open to let the air out of the coolant system. I couldn't understand on the phone exactly where this is. I think he said on the top by the thermostat?

If someone could point me to this plug to let air out of the coolant system and tell me the procedure I would really appreciate it. Any other tips would be great too!

Thanks,

Greg

 

[peaman]

three places where it is possible to add coolant; 1/ on the engine, 2/ in a metal reservoir and 3/ in a plastic reservoir.

On my engine, the fill cap on the engine itself is actually wired shut and labelled "Do not open". No problem. Normally, you should check and fill only in the second container which should be higher that the engine, and should be connected with a hose which is arranged so coolant can drain down, and importantly so air and vapor from the engine can rise up and back to that upper metal reservoir. If there is a high spot in the connecting hose, there will be an "air lock" which will prevent coolant from freely draining into the engine.

The plastic reservoir is an overflow tank and should only ever need to be partially full. As the engine warms up, the coolant in the engine will expand. If the expansion causes the pressure to increase a certain amount, coolant will be pushed from the second metal tank into the plastic overflow tank. As the engine cools down, that overflow may get pulled back into the second tank. You don't really need to worry about the plastic tank, as long as there is a small amount of coolant in it: it may have markings on it indicating "Level when cold" and/or "Level when warm". You should periodically check the coolant level only in the second, metal tank, and add coolant as needed.

 

[Kenneth K]

This shows the petcock on top of the thermostat housing. It sits higher than the manifold ("radiator") cap, and directly above the thermostat. The one on my engine is frozen though, so I've never been able to use it.

 

[Frank Langer]

If you have the Petcock mentioned in the above post, wait until the engine is cold, then remove the lid from the metal tank, then open the pet cock holding a tissue or cloth ready. You should get air bubbles, then eventually coolant with no air. Then close the Petcock and close the lid on the metal tank. On my 1984 E30+ with the same engine and tanks as yours, I added another Petcock best the thermostat on a small tube that was higher than the thermostat Petcock.
I go through this procedure after every sail, or after about 6 engine hours if I get a bit lazy, once the engine has cooled, and now mine never overheats. If you don't do this regularly, your engine will likely overheat periodically, which is bad for the engine. I don't understand why air continues to get into the system, but it does.
Frank

 

[Christian Williams]

If the metal reservoir is the highest point, leave the cap off as the engine runs and that should expel air.

If you're already doing that, is the reservoir definitely the highest point in the system?

 

[Stuphoto]

I always start with the basics.
Are you certain the thermostat is opening?
Plus the waterpump is working.

 

[Dave G.]

I use Christian's method as the metal tank IS the highest spot so the air will rise to it and out with the cap off. Let it run for a while so you know the thermostat has opened too.

 

[David Grimm]

My 38-200 has the engine under the kitchen sink mid ship. The coolant hoses that go to the metal tank pass unser the floor boards and attach to the top of the engine. I find air gets trapped there. I purchased an inline bleeder to help with this. Being that you changed the heat exchanger now may be the perfect time for a new thermostat as well.

Look at this on eBay

Easy Bleeder Cooling System Air Bleeding System Fits 5/8" Radiator Hose | eBay

Drive vehicle for 2-3 miles keeping an eye on the temperature gauge. It is not uncommon to see fluctuation in the temperature. Carefully open the Easy Bleeder valve, if no air purges from the Easy Bleeder just liquid your done.

www.ebay.com

 

[Alan Gomes]

I'm not sure whether this would help you, but I've outlined the procedure (below) from when I used to have a Universal M25XP in a previous boat. I have shared this method with others, and I simply cut and pasted it from my files.

Alan

I thought it might be helpful to mention a way to avoid airlock (and hence overheating) when you replace the coolant:

Take off the 3/8” hose at the bottom of the thermostat housing. (This is the hose that goes to the water heater.) You then refill the system through this hose. The best way is to get one of those hand pumps like this:



You can probably find an even cheaper one of these at Harbor Freight that might do the job for you.

Pump the coolant through the system until it fills up the manifold and starts coming out the hose nipple at the bottom of the thermostat housing, i.e., the nipple from which you just removed the hose. You might want to position a cup or something to catch the overflow. Then remove the 3/8” hose from the hand pump and reconnect it to the thermostat housing. You should not have any airlock at this point.

If you don’t have a pump you can accomplish the job by raising the 3/8” hose as high as possible and filling it through a funnel, letting gravity do the work. I was able to do it successfully using this method but it was very slow, whereas the hand pump will do it lickety split.

I highly recommend this method as sometimes it can be quite an ordeal getting a stubborn airlock out of the system.

 

[cruis-n]

In addition to other's suggestions, I found that squeezing the coolant hose (by hand) may help to "pump" out the trapped air. When that doesn't get any more air out, start the engine and have someone watch the temp gauge When it starts climbing (it'll be obvious), open the petcock slightly with a paper towel or rag covering the petcock and let out the trapped air/steam. Be careful, steam burns are not pleasant. The temp on the guage should immediately drop back to normal range. This may take a number of cycles to fully purge the system. Of course make sure the metal expansion tank has plenty of coolant in it.