EH700 175 HP I was losing coolant on one engine, not in the oil and no steam out the exhaust. I noticed staining around the pump on the front of the engine and not wanting to tackle that job right away, I drilled the cap so the engine was running at zero coolant system pressure to help preserve my coolant. Amazing, I began to gain coolant. The only thing I can think of is that the seal on the end of the tube bundle is leaking or the bundle it's self is leaking. I pressure tested it when I started losing coolant some time ago and it held 10 lbs for several hours at which time I took the tester off. Have not done it again lately. Any ideas? It's the only logical source. Did not taste any salt in the coolant. Yck.
The "O" rings at the ends of the coolant bundles.
A fact - coolant mixed 50:50 with Di water will show no conductance when placed in a small plastic up.
Once you have some 'contamination' the conductance will change quickly and head towards very few ohms.
"I noticed staining around the pump on the front of the engine and not wanting to tackle that job right away,"
Look at the weep hole directly under the fresh water pump shaft - is it leaking there?
Have you lubed that pump shaft lately?
These seals can be done by any pump place that handles rebuilding coolant water pumps.
tweekes wrote: I lube it regularly. So it is probably the O rings at the end of the bundles going bad? I will call North Harbor. Thanks, TW
If the pump leaks out of the weep hole then your pump seal was beginning to fail - they usually drip very slowly for a couple of years before it gets too bad. A while back when I had these engines in a couple of Bays I rebuilt one pump and purchased another one outright both with good results.
It is a good idea to lube that spot but very gingerly - over pressuring that zerc can cause problems like a leak.
Separately but related you now have the coolant volume 'growing' which is not from a leak. When you drilled a hole in the pressure cap you also allowed the pressure to reverse between the coolant and the raw water sides of the system. Now it is possible that the raw water is 'pushing' at the "O" ring rather than the other way around and the seal maybe compromised. If you are getting raw water into the coolant than its likely the "O" rings. If you are getting fresh water into the coolant than look to see if you have a water heater or space heater hooked up to the coolant lines which are beginning to fail.
Lilley two problems - confirm water pump seal / determine where extra coolant is coming from.