Heat Exchangers?? Need Advice, PLEASE!

OK......here's the back story......I am finally getting my '91 3807 out on the water. I have Cummins BTA 6 cylinder diesels. The port block was replaced about 50 hours ago, starts and runs instantly, and performs flawlessly so far.

The Starboard is a different story. Hard start when cold, starts fine once warmed up, smokes (white) a lot upon start-up but clears up within minutes.

But that's not my concern.

My concern is that since this boat is new to me, after about 5 hours of running, I moved all the salon furniture, rolled up the new rug, and got down in the engine room to see if everything looked ok, and check all the fluids.

Low and Behold, the Port side looked fine in every way, but the Starboard side needed 3 full GALLONS of anti-freeze mix to top it off! The oil looked fine, no sign of anti-freeze infiltration, and there wasn't a drop of anti-freeze in the bilge or anywhere on or near the engine.

I put a pressure unit on the engine's antifreeze filler tube and brought it up to 15 pounds. It was my hope I'd find a pin-hole in one of the hoses but that didn't happen.

What DID happen was the pressure gauge slowly dropped down to about 5 pounds, and when I re-checked the radiator, it was down a FULL GALLON!

Where did it GO???

NO sign of antifreeze anywhere in the bilge or on or near the engine. The only place I can think it went was out the exhaust, although I have no proof and maybe I am way off base, but I did lose a gallon of antifreeze into thin air!

Does this indicate a bad heat exchanger? I am confident they have never been cleaned or otherwise serviced or replaced, and the engine now has just over 1100 hours.

Should I just order a heat exchanger and new hoses that attach to it and install that, or is there a cheaper and simpler way? Or am I totally going in the wrong direction anyway?

PLEASE HELP?? I need to fix my boat and start practicing docking!!

Seriously....I would deeply appreciate any and all advice offered!

If the head gasket is blown, would the engine still be able to maintain the same RPM's at the same temp (180) while cruising? My usual cruising speed is about 16-19 knots at 2200-2400 rpm and the motors both top out at 3100 rpms and around 26 knots, depending on the sea and how many people are aboard. (Keep in mind the water is still pretty cold here and I have had no more than 4 people on board during these runs.)

Both engines operate identically (maybe a bit more throttle, a tiny bit, to the starboard engine, but that could be a cable issue IMHO, since they're very stiff), and after the boat is warmed up neither engine smokes. That white smoke is only at start-up and it's brief.

Would an engine with a blown head gasket perform for all intents and purposes, other than the missing anti-freeze, the same as a healthy engine?

Temps on both motors run right at 180, except the last time I was out and the Starboard engine went to 200 under full throttle, then backed right back down to 180 when I let off the hammer. I feel that was a result of the low anti-freeze level at the time since it took 3 gallons to fill it back up when I checked the fluids.

And would a blown head gasket take that gallon of anti-freeze I lost doing the pressure test today into the engine? I restarted the engine after refilling and it started immediately with only a slight amount of white smoke since I had already started it earlier.

Anybody else also think I should be looking for a blown head gasket? NOT a heat exchanger problem? I don't want to order $1500 worth of parts (heat exchanger, hoses, etc) if that's not going to cure my problem!

Capt J....are you thinking one or more of the tubes in the heat exchanger may be leaking into the sea-water surrounding them and then exiting that way? How would I test for that? Please explain again if that's what you're saying....sorry, but I am totally new at this and really confused, but trying to do as much work as I can myself. If that's not what you're saying sorry for misunderstanding but please explain what you're saying I should be looking for an how to do it. Thanks so much for your advice!

Guys, thanks so much for the responses....can you please provide a couple fill-in details?

I tested at 15 PSI because my radiator cap is a 15.......please explain the danger of pumping the system to 15 psi? What can happen? (NOT challenging you....I want to learn.)

When you say remove the back end cap....do you mean the end facing the exhaust? (I know this may be a dumb question, I just want to be sure.)

Once I remove that cap, and then pump up, won't the antifreeze just flow out?

Is there ANY chance this is NOT the heat exchanger?

If it IS...then the tubes inside are leaking coolant into the surrounding seawater inside the chamber, right? And THAT would be how I am losing the coolant, if I understand the process of the HE correctly.


And what was the exhaust elbow issue?

Does it make sense to just replace it and all the hoses that connect it? (The hoses are all circa 1991 so I'd change those too,of course.

I understand exactly what you're saying and I too feel I am quickly getting out of my depth here, My previous mechanical experience is limited to the pre-EPA/CAT cars when I was a kid (when cars had carbs and you could tune up a car and and change the oil all in an hour!), and motorcycles, prior to EFI. (Same scenario.)

I don't understand Turbo's, I don't understand EFI, an above all, I don't understand MARINE engines, PARTICULARLY diesels, and how they work and how they cool themselves with a combination of antifreeze and sea-water via these "heat exchangers". I mean, I get it in theory, but that's about all.

I was trying to avoid the $100 X2 (he brings a helper every time) I pay my mechanic. I did that all winter and frankly I am REALLY sick of every thing costing 4 figures no matter how small the issue. If I can save money by eliminating the labor rate, that will help a LOT.

But I realize I am not ready to take on big projects yet, even though if it IS the HE, it looks like an EXTREMELY simple part to change out. (A couple bolts and a couple hoses, all easily accessible.)

But maybe it isn't the HE to begin with and I'd be ordering non-returnable parts to the tune of almost $2K when in fact the problem lies elsewhere.

So....OK.

I'll call my mechanic and he'll do the job.

But I intend to sit there watching the whole process beginning to end so I can learn. I have to. Owning a boat is a true joy when it's running right and all systems are working....not so much when once again I am opening the checkbook.

I'll do whatever I have to do and spend what I have to spend....I knew this was an expensive pastime going in. But I am NOT going to continue to pay for things that I can do myself. So this time, the mechanic does it.


NEXT time?

ME.

Just to make sure I am rightfully extremely worried now....am I understanding you guys correctly that by pumping up the coolant system to 15PSI for a few minutes, then finding it a gallon low with no sign of pinholes in hoses like I was hoping to find, or any coolant anywhere in the bilge, is it possible I forced a gallon of coolant right into the engine??? Right along with the oil? So that I should under no circumstances start the engine? Should I be draining the oil right away and replacing it? Or flushing the engine with something? How would that have happened by pressure testing the coolant system? Even if I used too much pressure for about 5 minutes?

Rest assured I am DEFINITELY calling in a diesel mechanic at this point, but I need to know what to expect he'll find! Have I really screwed up here with this test I attempted? Isn't it possible it went through the HE (which has a tube leading right into the exhaust) and out the exhaust if the HE is failing inside?

Sorry guys, but what you're hearing is a slight case of panic!