Why do 692TA's overheat

[bobk]

The two 692TA 425 HP engines on our new to us 48MY slowly overheated today during a sea trial with a mechanic aboard while running at 2100 rpm. The Chesapeak is quite warm now. Both engines returned to normal after throttling back. Oil pressure was good. The PO's records show one new and one reconditioned heat exchanger a couple of years back, and water pump impellers have about 50 hours on them. Coolant level is OK and the glycol mixture is about right. We had the bottom and running gear cleaned Monday. She seemed to be running right, just getting up to 200F, and maybe more if I had let her run.

Any thoughts on where to look for the problem? The mechanic said this is common in the warm water we have this time of year and suggested cleaning the HE's with muriatic acid, but I doubt it is the issue. Thoughts?

Bob

[Genesis]

It could be the H/Es.

It could also be raw water flow. If both engines were equally affected, then my money is on growth (needing cleaning) in both the H/Es and gear coolers.

If only one engine did it (or one was more affected than the other) then my money is on an obstruction of some kind in that engine's raw water system - usually in the gear cooler, but not always.

[Boss Lady]

Actually, he could be right, since marine growth in the raw water system creates a hard scale crust that acts like a ceramic insulator and prevents the water from close contact with the heat exchanger surfaces. He is not correct about the Chesapeake water temps affecting this, I have never seen this problem because even if the water temp was 100 degrees there is more than enough flow from the raw water side to evacuate the engine heat. I boil mine out every year as preventative maintenance, if you get your Detroits over 190 indicated, you are in the danger zone for serious problems. If it goes over 180 on both engines, you are exceeding the heat carrying capacity of the cooling system. due to something that affects both of them simultaneously, like marine scale, or seaweed blockage. If everything else is normal and it is heating, something is affecting the cooling system capaciity. Either on the raw water side or the coolant side. The physical cooling are surface is quite small, so anything that restricts the flow or becomes a barrier between the water and the heat exchanger will have significant reductions in cooling efficiencies. First check the obvious, have you checked the sea strainers for foriegn stuff like seaweed or other growths,or trash? You have a simple problem just find it and fix it. You may have to get out the acid, I like to use a small recirculating pump and a bucket, do not use straight acid since it will attack everything it contacts, I use a diluted solution and it will eat the marine scale quickly anyway without affecting your engine components like pure acid does.

[Genesis]

Yeah, never-exceed on Detroits is 195F. You don't want to know what usually happens if you ignore that. If your alarms aren't set for 195F maximum change them immediately.

Thermostats are fully open at 185F. That's where you have run out of cooling system capacity. Properly set up you with 425s and a clean cooling system (both fresh and raw water sides) you should be able to run on the pins without going over 180F in water up to about 85F, with a degree-for-degree rise beyond that. Over 90F raw water you can't run 92 Detroit turbo engines without using water and inhibitors hard or you WILL overheat - I don't care what the mechanics tell you. Never intentionally run through 185 - if you get there BACK OFF!

500s are a bit twitchier and demand a scrupulously clean system and NO restrictions on the raw water side. Covington did an evil thing and put the gear cooler on the suction side of the raw water system on most of these enignes, which does NOT HELP one bit, especially if you get the least bit of anything in there - and it happens a LOT. 535s and 550s USUALLY require a boost cooler if you expect to keep them from getting hot in the south, although up north they may be ok.

[Boss Lady]

Karl,

What if they are using car anti-freeze? Or too high anti-freeze ratio? that may cause it to overheat as well.

Chris

[Genesis]

Don't EVER run car antifreeze in a diesel. It has ZERO cavitation protection and on a wet liner engine you will destroy the motor. It'll take a while but the damage is progressive and irreversable.

In reality ANY concentration of EG is "too much" if you don't need freeze protection. If you DO, then you should run only how much you NEED. 50/50 is a compromise number that is designed for CARS, which often have to sit out in subzero temperatures and then be started and run. If its that cold out the water you want to boat on is usually SOLID!

There is no reason on God's Green Earth to run that in a mechanical Detroit UNLESS you simply don't want to deal with changing it for the winter (e.g. filling with higher concentrations as part of winterization, etc) In that case AND IF you have enough cooling system capacity, have at it. In non-freeze areas with year-round boating you're simply making work for yourself and spending unnecessary money by doing this sort of thing, along with taking more environmental risk - EG is toxic and is a reportable spill. Distilled water and inhibitors are arguably not (the nitrates aren't great, but I doubt they're considered a pollutant requiring mandatory reporting - although you never know!)

These are NOT car motors and they're also NOT the newer marine engines designed to run at 195-205F - both of which have 15lb caps on their systems. Detroits run SEVEN psi caps and their normal operating temperatures should simply never be over 185F. It is true that higher operating temperatures lead to better efficiency, but ONLY IF THE ENIGNE IS DESIGNED FOR IT. Detroits are NOT.

If you insist (or must) run 50/50 on a Detroit and keep having temperature creep problems (and you are liklely to on a high output engine, especially beyond 425HP on a 6V92) the best solution for the Covington engines in particular is to figure out how to move the @#$@)%)@!# gear cooler to the pressure side of the system. Its NOT trivial; I would have done it if it were. There's an auxiliary core in the main H/E that in theory can be used for gear oil (that's why it was there originally) but when I talked to Covington about it they told me the reason it wasn't used was that on higher-output engines it had insufficient capacity to keep the GEAR OIL cool and the result would be burned up gears! The problem is that placing restrictions on the suction side of a pump does severe damage to its water-movement capacity, AND gear coolers are GREAT places for crap to get stuck, so you're trading one devil for another. Oh, and gears are cheaper than mains - but both are a royal pain if you blow them up.

One potential solution that I never was able to run down satisfactorily is to find a combination gear/fuel cooler and place it in the system where the current fuel cooler is. If you can find a suitable cooler that will do this (Sendure would be the place to start) this would be an EXCELLENT solution - but its not a cheap one. Expect to spend a few boat-bucks (and not the Benjamins either) on that modification - but it's the next step if you can't get the maintenance interval on these coolers under control.

In warm waters you can be stuck with an "every year" requirement on the main H/Es and gear coolers with Detroits. On-engine methods (e.g. my famous "phosphoric acid" method) do work but do nothing for the freshwater side - if that's gunked up and it can happen then you need to pull the core and take it to a radiator shop.

[Boss Lady]

I run the inhibitors, but I have seen everything at some point or another, I presume that our thread was started by a new owner, and I was attempting to bring to his attention that he needs to inspect first hand this type of thing or unless he has plenty of money to burn he can keep relying on people who will not take the time to be thorough. Like if he paid for a survey, the coolant report would tell him what the engines are filled with and current condition, a lot of my northern friends do in fact run anti-freeze. But they also do other things that I would never do, like vote for Ted Kennedy, LOL. Karl you always can be relied upon to provide excellent information, and you even get me thinking a lot, which I greatly enjoy the company of those who know more about something than I do.

[bobk]

It could be the H/Es.

It could also be raw water flow. If both engines were equally affected, then my money is on growth (needing cleaning) in both the H/Es and gear coolers.

If only one engine did it (or one was more affected than the other) then my money is on an obstruction of some kind in that engine's raw water system - usually in the gear cooler, but not always.

Karl, they are equally effected. How does one best clean the HE's and gear coolers? Is there a way to pump acid through with out removing them?

Bob

[SeaEric]

When I had my 42 Post with 671ti 450's here on the Chesapeake, I would run water in the cooling system in the height of summer. The Bay water does get very warm here, and the "coolant" mixture did not run as cool. When I would switch to water I had not more overheat probs. This after doing all the usual cooling system gymnastics and thousands of dollars to make sure all else was OK. A mechanic told me once that if you take the ambient sea water temp and add 100 degrees, thats the temp to expect a properly running engine cooling system to be able to maintain the engines. The Bay does get to 90 degrees at times. 90+100=190. The PIA is having to go back to antifreeze every winter. Perhaps there is a more high-tech solution, but this one worked for me.

[bobk]

I am a new owner and come from a trawler with a single 135 HP Lehman. And we are going to take the 48MY south this winter just as we have the done with the trawmer for the past several years. So, guys, please bear with me as I look for info.

The sea strainers were not checked, thanks for that reminder. They are both outboard and hard for me to get to at my size and age. I'll have them looked at today.

How do I recirculate phosphoric acid through the HE's and gear coolers? And where do you get the acid? The only common source is I know of is toilet bowl cleaner. Sulfamic acid is also used for cleaning toilets and steam pipes? Would this be OK for the HE's?

The surveyors and mechanics never suggested analysis of the coolant. Both are near 50/50 based on the simple floating ball automotive hydrometer. We can drain some and increase the water ratio. These engines were maintained by a guy who used to be a DD mechanic and now specializes in MAN's, so I'd hope he did it right. BUT, where do I get just the additives to put into the water that will replace the glycol mix? We will have some frost before we head south, but not likely any freeze so I'm comfortable with just a low concentration of glycol.

Thanks for all the advice.
Bob