Diesel engine question: Coolant cap replaced by elbow and hose....?

[Frosty]

See next post for photo

Hi folks,

Pardon in advance any stupid terminology - I've been running outboards for a long time, and have forgotten most of what little I ever knew about diesels. This question isn't about any particular engine/brand, but refers to something I've seen on a few different engines when perusing boats online. This photo is a random engine grabbed from "images" on a search engine, to illustrate. It is in the same general "range" of engines that would be in boats I'm interested in (tho not necessarily Volvo). Smaller, say 80's or 90's vintage at newest.

In the photo you can see on the left top there is what looks like a radiator cap you'd have on a car (at least back in the day). So I presume that is part of the cooling system. Okay, but on several engines (various boats for sale, etc.) I've seen where someone removed that cap, and in its place is what looks like a bronze pipe elbow, then a clearly-added hose that runs across the top of the engine and disappears down into the bilge (possibly into a bottle?).

Is this some sort of acceptable overflow system? Or just a complete hack and something to make a person run the other direction? Or a third option, a mild hack that could/should be reversed or solved in some other way?

Is there a reason that would suddenly make something like this desireable, given that it was clearly not on the engine as -built? Perhaps a newer way of doing things? Or a sign of an engine issue that someone was trying to compensate for?

(I couldn't find my photo of one of the modified engines, but hopefully its simple enough that words described it.)

Thank you.

 

[Frosty]

Okay, photo somehow didn't attach. Let me try again.

This engine has the original cap (red arrow), not an added elbow/hose as I described above.

 

[Diep]

I am not exactly a diesel engine expert, but these allow the coolant to vent/overflow when it heats up and expands. I believe there would be a straw on the hose down into the overflow reservoir allowing the fluid to be withdrawn again when the engine cools.

I don't know all the reasons for it but having such a setup gives you some level of visual inspection ability for the coolant level and condition. Otherwise you would need to open the radiator cap to observe anything.

I seem to see more variation in one of my motors which also routes through the water heater. Bigger circuit, more coolant, more expansion. Both motors have this type of set up though.

 

[Frosty]

Thanks, Diep

Probably the bottles were out of view in the various photos. Main point for me was to find out if these were some kind of band-aid to "fix" a more serious internal engine problem.

Some of the ones I've seen looked like there might be a better way to do it (vs. an elbow sealed into the top of the engine and a PVC hose -- like you'd use for potable water -- lying across the top of the engine, etc.)

Is having coolant overflow bottle on a marine diesel a "newer" thing? (So not customarily on 80's engines?)

 

[BruceK]

...Is having coolant overflow bottle on a marine diesel a "newer" thing? (So not customarily on 80's engines?)

Yes. Eg,American Diesel make a conversion kit to retrofit Lehman engines. My mechanic used another brand kit, Mercruiser I think, to convert my L120s.

 

[SteveK]

My 50+ year old Lehmans had the bottles

 

[BruceK]

My 50+ year old Lehmans had the bottles

But not from the date of manufacture.

 

[Diep]

Yeah I have '87 Cummins and it is definitely a retrofit.

 

[luna]

I don't think Frosty is talking about the 1/4" diameter tubing that delivers coolant to and extracts coolant from, the overflow bottle. It was mentioned that the Rad,. Cap on the engine was removed and a bronze elbow and hose put in it's place. That seems odd.

Closed coolant systems need to run under pressure. How is that achieved without a Rad. Cap or = ?

Perhaps Frosty can search again for the picture and attach it to the next post. Otherwise we are all guessing.

 

[Frosty]

I don't think Frosty is talking about the 1/4" diameter tubing that delivers coolant to and extracts coolant from, the overflow bottle. It was mentioned that the Rad,. Cap on the engine was removed and a bronze elbow and hose put in it's place. That seems odd.


Perhaps Frosty can search again for the picture and attach it to the next post. Otherwise we are all guessing.

Yes, you are on to what I was asking about.

That's what I wondered too. Given that the stock caps look like automotive radiatior caps (which have a spring and a set amount of pressure as I understand it), how does this work with a tube? Even if it goes into a bottle?

And.... presuming these are "hacks" (I have seen this a few times now on different engines.) Are they misguided hacks that could be straightened out? Or are they something that is a band-aid on damage --- or that could cause damage?

I dug around and found one example. I seem to have better luck putting photos in their own post, so see the following post.

 

[Frosty]

Okay so these are the same engine model. The first one is stock. The second one (two pics) has the elbow in place of the cap and then a sad looking PVC hose. The hose *may* got into a plastic bottle that looks kind of like an overflow bottle.

But the bottle part I understand, if it's a retrofitted overflow type thing. What I don't get is.... why is the cap completely gone? How do you now "get in there" (as in when you would normally remove the cap?

Does something like this cause damage? Hide a problem? Or are these just some people's idea of a "fix" and they could be reversed and better implemented by a new caretaker?

The first couple of times I saw a setup like this, I wondered but just left it at that. After I saw two or three different (yet similar) ones, I decided to ask those that know more than I do. Genuinely curious!

 

[Lepke]

Coolant is under pressure because water boils @ 212°F, 50/50 coolant boils at 224°F, and a 15 psi cap raises the boiling point by 45°F.
If your engine gets hot w/o a pressure cap, it boils over. Steam is created in the engine. Steam doesn't transfer heat as well as coolant. So your engine gets very hot and some damage. Maybe major damage.
You can run w/o pressure, but you need to make sure the engine doesn't run hot.

 

[Frosty]

If your engine gets hot w/o a pressure cap, it boils over. Steam is created in the engine. Steam doesn't transfer heat as well as coolant. So your engine gets very hot and some damage. Maybe major damage.

Aha, interesting. So an engine with this type of mod (hack?) could have been run in a somewhat overheated condition (if the operator were not careful; but then do careful people run a PVC hose right over the top of the engine?)

To be clear, this is not my boat or engine. But I have seen an arrangement like this a few times when looking over boats (in photos) and finally decided to ask about it. Wondered if it was a "run away, far far away" type thing. And too, just wanted to understand what was going on.

 

[kapnd]

Speculating that such a modification might have been made to allow the system to operate without pressure in order to keep it from leaking? Old mechanics trick was to use a lower rated cap to ease pressure on a compromised radiator.

 

[Diep]

I missed the point that the picture in post #2 was not the situation under discussion.

I talked to a guy once who said the radiator caps needed to be kept loose on a pair of old Detroits "because they got overheated and needed new head gaskets" Maybe related to post #14.

Like I said, I'm no expert but interested in the topic.

 

[BruceK]

In a conversion, isn`t the existing "radiator" style cap replaced with a solid plate and the cap on the expansion bottle does the management of pressure? I think that`s how Lehman does it, plus some tube gets replaced or added and epoxied on, memory foggy on that.

 

[Frosty]

Bruce,

Aha, interesting. In one of the photos of the "pipe elbow" engine you can just see a round translucent bottle at the bottom of the photo. (The "normal" engine with the normal cap doesn't have that bottle anywhere visible.)

The hose though, looks to drop down below and past the bottle, then disappear in a direction that doesn't make it look like it ever connects with the bottle, even down low. Hmm.

Diep: Sorry about the confusion. I should have tried to find the other photos before posting the thread. But then too, I figured maybe it was some kind of mod everyone (but me) knew about and hence it would be obvious by my description. My bad.

 

[SteveK]

The hose though, looks to drop down below and past the bottle, then disappear in a direction that doesn't make it look like it ever connects with the bottle

I spotted that too, but I am not familiar with this engine, so was waiting for someone that either recognised that as normal on some. But the hose does not look like any OEM hose for that purpose.
If that hose connects into that bottle then it is an oversized DIY expansion device, which without a pressure cap to regulate still does not make sense. The hose may also discharge into the bilge, again does not make sense.
Hope someone recognises this setup and has an explanation.

 

[Lepke]

A proper pressure cap setup allows coolant to escape when over pressure. The temperature also goes down. There is a relationship between pressure, temperature, and volume. The small hose or tubing leading from the pressure cap housing goes to the overflow bottle bottom. Or if going to the top of the bottle, the hose extends to near the bottom. Later when the engine cools, a vacuum is created inside the coolant system and draws coolant back to the engine. If the overflow tube went to the top of the bottle, it would draw air. Properly configured, the overflow system will expel any air left in the engine from its' initial filling, and later when cooling, refilling with coolant.
The large hose in the picture is unlikely to push any air to an overflow bottle. It will stay in the hose and eventually be drawn back into the engine.

 

[twistedtree]

I suspect it's some sort of hack. Without a 2-stage pressure cap, I don't see how it can be operating like a "normal" expansion bottle that fills and empties as engine temp cycles. But maybe it still does somehow.

As for filling the system, I see a second radiator cap on top of what looks like the thermostat housing, center front on the engine. On the modified engine, it looks like a screw cap rather than a radiator cap. I think this further suggests that the modified engine operates with the coolant at atmospheric pressure rather than elevated pressure. Again, I don't know why, but I'd guess a hack to work around leakage of some sort.

 

[Frosty]

Thanks for all your thoughts.

I've learned more about how that type of system is supposed to work. It also seems pretty clear that something like this is a hack.

Presuming I absorbed all this correctly, it seems that questions remain that could probably only be answered by knowing more about a particular situation and engine:

1) Whether it's a hack that -- if you "undid" it -- everything would be fine and back to as-built.

2) Whether its a hack that may actually have caused the engine to run hot or overheat.

3) Or whether it's a hack that was put in place to "fix" something that was already wrong (e.g. leakage).

Basically: Whyyyy.

 

[twistedtree]

Basically: Whyyyy.

Exactly. All you really know is that it was done for a reason, because nobody is looking for random things on a boat to just change for the hell of it.

 

[Bacchus]

The cap regulates the coolant pressure so without it I have to guess the coolant operates at atmospheric pressure rather than the usual 15 +/-PSI. I can only guess that the "system" leaked somewhere? under pressure and eliminating the pressure solved the leak.
Does the fitting at top of the coolant reservoir have the provision for the 1/4" overflow tubing or has the typical fitting been completely removed?

 

[Frosty]

Does the fitting at top of the coolant reservoir have the provision for the 1/4" overflow tubing or has the typical fitting been completely removed?

It's only photos, but I sure don't see anything but a pipe elbow "sealed" into the opening and a ~1" PVC hose going from the elbow to .... the bilge it looks like. I cannot see any evidence that there is 1/4" overflow tubing there.

(Can anyone else?)

(Second and third photos in post #11 of this thread)

 

[Bmarler]

What an interesting arrangement. I’m thinking we’re assuming the hose across the engine is connected to the plastic bottle. Definitely no pressure control.
Also interesting that the coolant header/reservoir is on the exhaust manifold. Don’t remember seeing that before.

 

[Frosty]

What an interesting arrangement. I’m thinking we’re assuming the hose across the engine is connected to the plastic bottle. Definitely no pressure control.

It seems like that PVC hose "should" be going to that round bottle (of which there isn't one on the comparison "stock" engine), but it sure doesn't look like it does in the photos. It looks like the hose drops down and curves (natural curve of hose) away from the bottle and toward the engine again (dropping down into the bilge). But of course there were no more detailed photos, grrr.

Based on what I've learned here I'm thinking probably it was done to "fix" leaks, and/or the person didn't understand the pressure nature of the system (?). Unfortunate, if so.

 

[C lectric]

It may also be a coolant recovery setup.

For those, you must have a COOLANT RECOVERY CAP in which there are TWO VALVES.
One valve to release pressure and feed expanded overflow coolant to a bottle mounted somewhere. Bottle best if mounted at close to the same level as the expansion outlet or Rad. CAP..

The other valve allows the coolant system to suck the expelled coolant back into the engine as the engine cools off when no longer running or if the load has dropped a lot.
The hose between the valves and bottle are connected between the RAD cap mounting and the BOTTOM of the collection bottle. This hose also needs to be clamped at both ends, maybe lightly but still clamped.

These systems have been installed in cars for many years now to prevent loss of coolant onto the road.
This has the advantage of not dumping coolant into the bilge or on the road as antifreeze is poisonous.

I installed one of these KITS on my engine many years ago, 35 yrs +. It works and well.
I can pop the engine hatch upon shutdown to have a look at the bottle level. If not at the appropriate high level then there is a leak which I have to find.

Upon the shutdown cooldown, suckback, I can also look and if the level has not dropped after several hours then I have an airleak. Some snugging of clamps fixes the air leak so the bottle level will rise and fall as the engine heats and cools.

I also carry a spare cap, RECOVERY TYPE, for the engine and if the snugging does not fix the problem then either the cap needs to be replaced OR some dirt has gotten in the cap mounting/sealing area and needs to be cleaned.

Yes, the cap should be inspected from time to time. Done ONLY when the engine is cold or you may get sprayed and scalded with HOT coolant.
Burns and/or blinding have resulted.
Even then I use a heavy cloth to cover the cap. Some engines, depending upon their size, may hold the heat for longer than expected { up to two or more days) and spray when the cap is loosened.

THe spray will be less but could still be dangerous.

 

[Frosty]

It may also be a coolant recovery setup.

For those, you must have a COOLANT RECOVERY CAP in which there are TWO VALVES.
One valve to release pressure and feed expanded overflow coolant to a bottle mounted somewhere. Bottle best if mounted at close to the same level as the expansion outlet or Rad. CAP..

C lectric,

If you have time, would you be able to put an arrow or something on one of the two photos of the engine with the PVC-hose-and-elbow arrangment to show me what you are seeing that might be a coolant recovery setup? It's the second and third photos in post #11. I'm not seeing it; but no surprise as I'm basically a diesel newbie. Learning as I go.

Even though it's not my engine, I would rather know it's something "decent" rather than just a hack that might be detrimental. Especially because I've seen others with something similar. Always wondered.

 

[C lectric]

A closer and more carefull photo examination makes it appear to be my mistake.
Sorry about that.


However my description still stands but NOT apparently for this engine

If I were looking at this engine in person I would ask the mfgr, is there or can there be a coolant recovery system rigged.

 

[SteveK]

If you enlarge photo 3 the braided water line at the 1st tie appears collapsed as if from vaccum, my guess after hot fluids softened it. That suggests it is going into a container and being drawn back. JMO the one visible with 50 on cap may have a bottom connection point not seen.