Hot Water Heater heat exchanger disabled

I have a 1986 Ford Lehman 135 which was recently rebuilt. The hot water heater is 25 years old and leaking....so I am bypassing it with the fresh water. Problem is that there is a heat exchanger in the water heater, so I cut and plugged both hoses. Engine runs fine at about 7knts, but above that speed the engine begins to overheat. We have no need for a water heater so any suggestions on what I should do?? Should I connect the 2 hoses together? I know the best thing to do would be to replace the water heater and the heat exchanger which is solidly attached to the existing water heater unit but we really don't need hot water.
Thom

Welcome to the forum!

I'm a little confused. Normally you have a loop that runs from the engine to a heat exchanger in the water heater. Are you confusing the heat exchanger on the engine as being a water heater?

Ted

The way you are describing your setup is that there is a heat exchanger on the outside of the water heater.

What brand of water heater and how is the exterior mount heat exchanger plumbed into the water heater?

Right, the "loop" on my boat is now broken, as I have cut and plugged the loop.

Connnect the loop together, water will still flow through the system.. but at a reduced flow.
Hollywood

...what he says.

One hose flows into the WH and then out in a loop returning to the engine. They shouldn't be capped, they should be connected to complete the loop.

Your overheat problem is not the water heater loop. You either have insufficient raw water flow from a bad pump or a blocked engine and/or transmission cooler. Make sure the through-hull is not blocked. If none of that is the problem, check that the coolant jacket was properly burped, that the coolant water pump is working properly, belt tight etc. Then check that the thermostat is not stuck or failed.
Thinking more about it, I would do the "burping" first.

We are all assuming that the heat exchanger at the water heater is part of the water heater and not the heat exchanger for the engine. If that is not the case then the overheating would be caused by the lack of the heat exchanger for the engine. Plugging the water heater circuit would make no difference as this is an optional circuit on the Lehman 135 which can be plugged at the engine.

As to the overheating, Xsbank has given you the suggestions to check. Always the impeller first, then the 135s heat exchanger. If you are getting a good water flow out the stern then it could be a shortage of coolant or a blocked thermostat.

Had the identical problem on my 135. Opened the main heat exchanger on the engine and found caked salt blocking much of the water flow.

The water heater was just masking another coolant issue.


Like sitting in traffic on a hot day and turning on your heater to help cool the engine.


As Xsbank and Bay Pelican noted the water heater loop is extra (optional), etc.....unless of course it was hooked up incorrectly in the first place.


How long since engine rebuild? How long since raw water impeller change? was the old heat exchange used for the rebuild? the only way is to systematically check for good raw water and good coolant flow through the engine. Including checking the raw water temps as they enter and exit the main heat exchanger.....

As mentioned, the water heater (although it was leaking and making a mess) was indeed removing 'heat' from the engine. Now that you have lessened that heat removal by uninstalling the water heater you are seeing the true cooling capacity of your engine. Your engine didnt come this way from the factory. It has lessened over time.

I would tend to agree that either the water oil heat exchanger on the block is crudded up and/or the tranmission cooler is crudded up (or more like it, both)

Think about it this way. All the heat exchangers (on engine heat exchanger, transmission cooler and water heater) work to remove heat from the water and transfer it to the sea water on the way by. You removed a pretty good portion about 20% +- of the heat exchange ability by removing the water heater. Rather than put the water heater back, first clean up the engine and transmission heat exchangers. They are mission critical to the long term life of your engine.

Also, the water heaters' condition is probably pretty close to approximating your engines coolers and conditions.

As a quick fix, remove the plugs you put in the hoses, and use a metal hose barb fitting (not plastic) to allow the coolant to flow through the hose. Double hose clamps on each side.

About 30 hours on the engine. I'll check out the other suggestions. I'm new to this, so really appreciate your comments.
Thom

"You removed a pretty good portion about 20% +- of the heat exchange ability by removing the water heater."

It usually takes 35 -60 min to have the contents of the heater tank up to engine temperature . After that the HW heater does no circ water cooling.

couldn't it be the way his was plumbed the line to the water heater was a major line in the heat circuit that HAS to be in a loop ( vs. capped) or the motor doesn't move enough coolant... I have seen them done that way vs. a circuit that CAN be plugged (or shut off completely ) .. that is my thoughts on his issue.
HOLLYWOOD

FF said:

"You removed a pretty good portion about 20% +- of the heat exchange ability by removing the water heater."

It usually takes 35 -60 min to have the contents of the heater tank up to engine temperature . After that the HW heater does no circ water cooling.

Click to expand...

Ever gone down and felt near, around and on the hoses, and water heater while underway. There is usually a considerable amount of heat being put out. That's Calorie sink no matter how you look at it. With the heater hoses bypassed the lopped off internal amount of coolant being circulated is cut down. In an old engine (even if 'rebuilt') the interior passages, heat exchangers and the like will not be 'like new'. I am not familiar with Lehmans, but it would not surprise me if there is a fitting in the coolant pipe which shunts off the water heater coolant that forces the coolant down the loop, which is in turn restricting the flow to the heat exchanger.

OP, have you asked the rebuild shop if they cleaned out the heat exchangers as part of the rebuild? That would be an excellent question for them tomorrow. Also, was the water injection elbow replaced at re-installation? Are you seeing the 'usual' amount of water out of the exhaust when running?

You mentioned this happened after you removed the hoses from the cooler. I believe you have to 'burp' a lehman cooling system. Not only have you reduced flow from the plugged hoses, you probably have an air pocket in the block which is impinging water flow causing this. Read up on "removing air from lehman 120 cooling system' on internet. Lots of ideas, sounds a lot like yours. Maybe a water supply problem also. Lots of things to look at.