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Overflowing Coolant

themons

Member
"Hello:

After searching thr


"Hello:

After searching through 150 posts on coolant, I still need some help on figuring this out.

The engine is a FWC 1988 350-454.

When running the temperature gauge stays at 165 and I am certain that it is working properly.

However, coolant is forced out of the system into the reservoir which sooner or later overflows. When the engine cools down the remaining coolant drains back into the system to the point that there is no longer any coolant in the resevoir.

I am concerned that the coolant that is suppose to be in the exhaust manifold and the hoses between the exhaust manifold and the heat exchanger is also no longer there.

Could this be caused by an air lock and boiling the limited amount of coolant in the system?

Thanks."
 
"The running temp is good, lik

"The running temp is good, like you say. So, the engine constantly runs coolant out the overflow tube? I'd say either the system wasn't quite filled (do you use the thermo housing bleeder?), or the system is not actually sealed. Meaning, the head gasket is leaking, the elbow/riser joint is bad, the cap to HE header seal is bad, or other leaks. I'd pressure test the system, full, warm, at 7psi."
 
"And make sure the H/E cap is

"And make sure the H/E cap is seated all the way and also pressure tests OK. If you have twin engines, just swap the caps and see if the problem moves. I believe the cap should be 7 lbs."
 
"If the cap is tight and the s

"If the cap is tight and the system has no trapped air, the only other cause is a blown head gasket.

Let's all hope it's the cap!

Jeff"
 
if the fwc system also does th

if the fwc system also does the exhaust mans you could get pressure from a bad gasket at the block off plate between the man and riser-would be better than a blown HG-pressure test the system is the only way to deffer between HG or riser gasket.
 
Could raw water be forcing the

Could raw water be forcing the coolant out? I'm thinking heat exchanger with an internal leak.
 
"This is a interesting problem

"This is a interesting problem. I have the same situation, coolant overflow to the recovery tank, except, it is with my Onan generator. Thought it was a head gasket, but a compression check read the same for both cylinders (142 PSI. Thought it may be the cooling pump, removed it,took it home, clean and tested with batteries here and it works fine. Next step was the heat exchanger, removed that, took it home, tested and cleaned it and it is OK. Replaced the impeller in the raw water cooling and check all the hoses there, still the problem of overflowing.

I found a post on the Trawler forum that one person had the same problem. I sent him a email and got a answer last night. He solved this problem (ONAN) by cleaning out the exhaust manifold because rust and gunk had it clogged. So, I will try this tomorrow."
 
"Check the cap with a pressure

"Check the cap with a pressure tester in its normal operating position. Sounds like the vacuum relief valve isn't seating.

As suggested about, another easy option is to swap caps. If issue follows the cap, replace it. If you don't know how old the caps are, order two if you need the replacement as the other probably isn't too far behind."
 
"A raw water leak will not pus

"A raw water leak will not push coolant out of the exchanger since raw water pressure is lower.

A leaking block off plate on the manifolds will allow coolant to leak into the exhaust and out the back, but it will not add pressure to the coolant (which is at a higher pressure).

Jeff"
 
"Hi Makomark, I have not done

"Hi Makomark, I have not done a pressure test because it is a tool I do not have, but now appears that I will have to get one. I may have
time to get to Harbor Freight this week and buy a tester. I hope this test will enable me to find the problem easily. Tiara dropped the generator into a compartment in the stern and it is not easy to get to.

Thanks for your help. Once I get this solved, I can begin on the 454's, I have a lot of ideas."
 
"You can borrow a test kit fro

"You can borrow a test kit from Auto Zone. Call around your area to see which store has one, then leave a deposit. No charge!

Jeff"
 
"Jeff took the words out of my

"Jeff took the words out of my mouth. Some advance stores lend/rent too.

There are a few tests you can do with a good tester. Best description is the owner's manual for a STANT tester (12270 - download from their www site). Don't forget to check the cap. The cap adapter should be included in the kit.

When the coolant exits, is it a violent expulsion or a steady dribble?"
 
""When the coolant exits,

""When the coolant exits, is it a violent expulsion or a steady dribble? "

When the overflow occurs, it is a slow steady rate, after 10 minutes of running, the coolant recovery tank is full to the top.. By then, the coolant is near boiling temperature, the tank is very hot."
 
"Leaking cap! I'll bet yo

"Leaking cap! I'll bet your a steak dinner on it.

As the Marked Man said, don't forget to test the cap as well.

Jeff"
 
"The cap should easy to replac

"The cap should easy to replace, 7 lbs PSI. It may be the cause because the generator only has 117 hours, a vintage 1988. Much like the engines, both have had little use over the years. The engines have 864 hours."
 
"If it is a "PITA" ins

"If it is a "PITA" installation, you may want to check the coolant condition when you crawl in. Not only the concentration but the pH as well. It should be well into the alkaline side."
 
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