Heat exchanger temperature measurement

[jruesr]

We have been trying to troubleshoot an engine over-temperature problem on two similar albin boats. One is a 32 and the other is a 32+2. Both have Cummins 370 6bta engines. The 32 works great and the 32+2 is overheating.

The fresh water exiting the heat exchanger (on its way back to the engine) is cooler than the fresh water entering the heat exchanger (comming from the hot engine). I refer to this as the temperature drop.

I ran two trials on the albin 32 and find the temperature drop to be 42 to 45 degrees F. 2400 rpm. Seawater 90 degrees.

On the 32+2 the temperature drop is only 23 to 24 degrees F. 2400 rpm . seawater 90 degrees. This is the engine having the issue.

What should the temperature drop be. What is typical. Does anyone have experience with this issue.

[jleonard]

1st define overheating. What temp?
When was the last impeller change? Last time the coolers were removed and serviced? That's where I would put my efforts rather than trying to define a temp delta.
Also make sure you're sea strainer cap is sealed. A tiny leak will cause a 10 deg to rise. Been there

[N4QC]

In my experience, the inlet water temperature has a significant impact on the cooling system. When I run a Yanmar 4lh-dte in 90 degree waters of Tampa Bay, I cut back on my cruising rpms. My cooling system is designed for a 77 f degree inlet water temperature. The flow of water is further reduced by the reduction in inlet hose and fitting sizes in the conversion from metric specifications, to ase use. Estimated efficiency loss is about 20% at 90 degrees…

You also have to be concerned with the overall heat build in the engine compartment. I run with an enhanced engine compartment ventilation system - blowers on all the time for air intake and air exhaust...

Jlenoard’s comments are also valid…

Happy researching,

[jruesr]

Thanks for the replies. The 32+2 is an extremely well maintained boat. This temperature problem just appeared on a cruise two years ago. The boat was very new to its owner at that time so past history is not certain. In order for it to run at normal temperatures in this warm water everything has to be very clean.

The boat has a new water pump and impeller. The aftercooler and the transmission cooler were cleaned before the first trials and the heat exchanger was just cleaned before the last trial. The mechanic says that he sees light through the heat exchanger fresh water side (from a flash light) and that is not normal. We are considering a new heat exchanger at this time. The boats are on charlotte harbor, Florida. The 32 is on the hard now so we can not do comparison trials now.

The mechanic has an impeccable reputation.

My question is why does the fresh water temperature fall 42 degrees when passing through the heat exchanger on one boat and only 23 degrees on the other boat. What should be expected. What is normal for other owners. Its easy to check and possibly would be a good thing for everyone to know, for reference, on there own boat to monitor the cooling systems condition.

We will definitely check the o-ring seal on the strainer. Thanks for everything so far.

In case my attachment did not get through I am trying again. The boat alarms at 202 degrees and after that we slow down and go home.

[denchen]

This may sound strange if you live in a hot climate area, but if anti freeze is added to the engine cooling water, the mix will absorb more heat quicker and will release the heat quicker in the heat exchanger. During World War 2 many aircraft had very small radiators so to get rid of the heat a strong concentration of anti freeze (glycol) was used as a coolerant, but be careful if it is too strong it becomes flammable. Hope this might help. .

[jruesr]

Replacing the heat exchanger, even though it had been cleaned, solved the problem. I will do temperature checks when the opportunity presents itself.

Thanks for the input.