Ragged Edge

[solanderi]

Owners of 92 series Detroits are well aware that these motors operate on the edge of the envelope in regards to cooling capacity. I run my boat, a 45C w/ 692's, off south florida which can get especially toasty in the summer time. My mechanic says he is invariably called each summer when owners report bumps in operating temps secondary to increased local water temps.

I was told about a product for 692's which is essentially an oil sump. I did a search on the HOF and did not see any threads with this topic. Of course the theory is that the sump creates a greater oil capacity (by 2 times) to heat up and therefore affords another level of protection from cooking your 92 series.

I appreciate any input or ideas.

Greg
1985 45C
Hat Time

 

[MikeP]

We did tests of exactly this (large capacity oil sumps) on auto engines for HP change and eng TEMP change. Can't imagine the results are any different with boat engines.

Temp wise it does nothing unless the sump is finned and exposed to substantial airflow. Even then the "improvement" is not much.

Water has 4 times the thermal conductivity ability compared to oil. Therefore, increasing the oil volume to help in this process does nothing meaningful. Additionally, the oil in the system is not cooled down to the same temp that the water is, thus lowering this "possible benefit" even further. If the oil sump is "finned" and exposed to airflow, it can provide some additional cooling. At 60MPH, we found differences averaging 5 degrees. If it is not in the airflow it has no effect at all since the engine will heat ALL the oil in the pan to the same temp. If there is 12 gal of oil instead of 6, it will just take a little longer for that oil to reach the "normal' temp. But you won't see any difference in the eng operating temp.

Scrupulous cleaning of the cooling system or providing additional capacity through larger Heat exchangers, etc is the only thing that is really going to help. In my OPINION, the HE and inter/aftercoolers should be REMOVED and cleaned every few years to maintain peak efficiency.

 

[Avenger]

If the sump is cooled it may have some benefit. Just adding capacity will only slow the process down, but the end result will be the same.

Cooling oil is a real pain since the oil near the cooler surface thickens as it cools and becomes a barrier to cooling the rest of the oil. That being said, oil does carry a fair amount of heat out of an engine, but it would probably be more cost effective to add a larger oil cooler. This assumes that your raw-water system will be able to handle the BTU's. Maybe our resident engineer knows how to figure that out.

 

[Genesis]

The best bet is a bigger (or second) H/E.

Unfortunately those options are a pain to put in place and damn expensive.

The H/E capacity on these engines is marginal at best; they were apparently originally sized (the H/Es) for ~300HP or so, and in higher horsepower versions you know what happens.....

 

[luckydave215]

The primary cooling media in our engines (or any four stroke engine) IS the oil. I can't remember seeing any designs with water cooled piston crowns, valve stems, cam lobes, main bearings, etc. The oil cools the hot parts by direct contact, and then sheds it's heat by exposure to the (cooler in comparison) block surfaces and oil cooler that have water cooling passeges on their "other" sides.
That being said, the oil temp is controlled by to a large extent (but not exclusively) by the water temperature, and lower water temperature is therefore the best and simplest way to achieve lower running temperatures overall.
As has been observed by others, our basic heat exchanger designs are rather feeble, and that's where effort should be applied. Why not adapt a large water-to-water industrial heat exchanger to replace the undersized stock one? It shouldn't cost that much if a non marine (non absurdly marked up in other words) unit is sourced, and for the connections, it's just adapter plates and hoses......

 

[solanderi]

Thanks for pointing me in the right direction w/ this. Has anyone on the HOF upgraded or replaced an OEM HE with a bigger or more efficient one ? Is there anyone who already designed or manufactured the fix for this shortcoming ? If not, how many on the HOF are 92 series owners and how many would be interested in a solution ? My engines are from 1985 but I bet the HOF has enough resources and out of the box thinkers in 2008 to solve this problem or at least substantially reduce the risk of an overheat.

Greg
1985 45C
Hat Time

 

[Finalee]

The 6v92 motors in my 43 dc stay under 180 in the summer. Measured with ir. They can run all day at 1900 rpm at that temp. Horsepower is 460. From prior posts it seems the higher horsepowers have the problem.

 

[captddis]

Thanks for pointing me in the right direction w/ this. Has anyone on the HOF upgraded or replaced an OEM HE with a bigger or more efficient one ? Is there anyone who already designed or manufactured the fix for this shortcoming ? If not, how many on the HOF are 92 series owners and how many would be interested in a solution ? My engines are from 1985 but I bet the HOF has enough resources and out of the box thinkers in 2008 to solve this problem or at least substantially reduce the risk of an overheat.

Greg
1985 45C
Hat Time

You don't replace the HE, you add a boost cooler. Not hard to do. Go look at the 550 hp forward plan engines. My 8v92s have the same HE as the 6v92. Mine run 180 in 90 degree water. Hovever I have TIs and the intercoolers are raw water cooled. The TAs have JWACs and that is why the boost coolers are needed.

 

[solanderi]

Does anyone have a web site reference for the boost cooler that capt ddis is referring to ? Genesis what are your thoughts about this ? Thank you,

Greg
1985 45C
Hat Time

 

[Top Shelf]

i've got Covington 8V92's and (Damn I know shouldn't say this....knock wood) I run 180/ 185 all summer long in South Florida as well. I've heard the boost cooler also called the fuel rerun cooler. My boost cooler, as well as the main H/E's are made by Sen-Dure. On these Engines raw water exists the RW pump and goes to the boost cooler first, then the main HE, risers, etc. On the 892's they're literally on top of the starter on the port side. Which makes starter service a real pleasent experience. Thx.

 

[Mambeaux]

Where is the BEST place to shoot with a IR thermometer for a true temperature reading?

 

[solanderi]

Here is the reference for the Sen-Dure company in Ft Lauderdale. Does Detroit Diesel / MTU make any of these parts to increase cooling capacity.

I also run at 180s all summer but ......you are only a few degrees off of MELTDOWN, and a date w/ Big Bill, correct ? Especially Biscayne Bay in the summer.



http://www.sen-dure.com/

 

[Top Shelf]

I was told to shoot the IRG right on the thermostat housings. The Engines are usually within a couple degrees of each other. thx.

 

[MikeP]

Make sure that whenever you are using an IR gun to compare surfaces, that you shoot both from the same distance and same angle. Otherwise you readings will not be accurate. Also if the surfaces are different materials or different colors, the readings will again not be accurate. ALSO, if your IR gun has a laser dot that projects onto the surface so you can "aim" it, be aware that the dot does not represent the sensing area - it is just an aiming point that is in approximately the middle of the sensing area which increases with distance.

 

[REBrueckner]

At 180 degrees engine coolant temperature, which seems hot, what's the approximate temperature of lube oil?? Or what's a typical temperature relationship between coolant and lube oil? How much hotter is lube oil??

Seems like there are only two options: increase heat exchanger surface area between raw water and coolant; increase raw water flow.

Seems like adding a second heat exchanger would be useful (but expensive) when the raw water cooling temperature has not been raised significantly after passing thru fuel coolers, coolant exchanger, and oil cooler...I believe my raw water temp increases roughly 8 or 10 degrees in passing thru my various 71 series coolers....so another heat exchanger WOULD provide significant additional cooling. (cooling is proportional to the temp difference of coolant and raw water.)

Other option: a higher capacity raw water pump....Don't believe I've ever seen a discussion of this...is the raw water system already operating at about maximum water flow??? Could another pump or impeller be used to increrase flow??

Are any of the following reasonable checks?

If you guys with high HP 92 series are right at the temperature edge, as implied above would it be a good idea to put in slightly lower temperature thermostats....so when 170's, for example, begin to result in 180 degree engine temps, or 160's begin to yield 170 or so, at normal cruise, you know it's time for a coolant system and or raw water system cleaning?

Or is it smarter to bump up RPM from time to time to be sure you have a satisfactory operating temp, say 200 RPM above your normal cruise...and a bit of cooling leeway....This is how I typically check my 71 series TI's.

 

[Genesis]

185F on a 170F thermostat is "full open" and you are out of cooling system capacity.

You can go from 185F to 215F in about 30 seconds, at which point you have hotspot boiloff in the block and/or head and compromised seals and/or a cracked cylinder head. Bang - you're rebuilding the engine.

 

[captddis]

All HP covingtons came with 160 degree t stats.

 

[Genesis]

185F on a 160 Tstat is beyond the cooling system's capacity as well.

I call 185F "never exceed" on a Detroit in marine service for a very good reason. I start getting nervous around 183ish; 180F is the maximum "normal operating" temperature I will accept.

Cylinder heads are expensive and liner seal failures on 92s are a ROYAL pain in the neck.

 

[captddis]

who said anything about 185 degree on a 160 stat? mine run 170 in cool water and never exceed 180 in the summer.

 

[Boss Lady]

They won't do that running the shallows in the Bahamas.