Smells like diesel in my coolant. Is that possible?

I just check fluid levels in my Cat 3208 turbo charged engines and my port engine was Full to the max. I do not have a recovery bottle and I do have some oil in the bilge. I stuck my finger in and it smell like diesel. I then stuck a paper towel in and it was some brownish parts and yes it smells like diesel. A few years back I had a failed heat exchanger on that engine and had to replace it so I know what it was like to stick my finger in the hole and have it come out black with oil. What do you think is happening here? Where would there be a transfer of diesel to coolant? Turbo intercooler maybe?

To clarify, you stuck your finger into the fluid in the bilge, or inside the coolant system via the cap?


If you remove your coolant cap and start the engine, do you see bubbles in there while it's running? Do you see unburnt red diesel or does it appear to have gone through combustion?


I did some quick research and it seems that this engine is prone to head gasket failure, which is what burnt diesel in the coolant system would indicate. See this thread: https://www.trawlerforum.com/forums/s6/cat-3208ta-head-gasket-replacement-56609.html

My engines are the 1991 425 HP 3208TA. I think that head gasket problem had been corrected by then. I guess I just don't know exactly where diesel can mix with the coolant. I understand oil and coolant relative to the head gasket. Where does the diesel come in?

If it's diesel that has been through the combustion process to some degree then it can be finding it's way through the head gasket and into coolant. If it's virgin diesel then that seems less likely, unless the compression in that cylinder is so bad that it's not combusting, but it seems that condition would be noticeable. The solution to your problem could be as simple as re-torquing all of your head bolts.


Harbor Freight sells a kit as well as the fluid to test the coolant yourself: https://www.harborfreight.com/combustion-leak-detector-64814.html


Since injection occurs in the cylinders (unlike turbocharged gasoline engines) I'm not sure how it could be getting in there otherwise...unless this engine differs from most turbo-diesels in that way

One question I didn't answer was that I stuck my finger and then a paper towel into the coolant tank. Since the coolant tank is getting full and overflowing into the bilge I know it is gaining in volume of fluid. On the paper towel I could see brown contamination and some pink.

Could you have a heat exchange leaking too? A bad head gasket or cracked head might put a little fuel in the coolant but hard to imagine it would overflow the tank. And a few pink spots on the paper towel is a tiny amount. Have you checked for salt or sodium in the coolant (assuming you're in salt water) ? I believe the labs that do oil analysis do coolant as well.

jgwinks said:

Could you have a heat exchange leaking too? A bad head gasket or cracked head might put a little fuel in the coolant but hard to imagine it would overflow the tank. And a few pink spots on the paper towel is a tiny amount. Have you checked for salt or sodium in the coolant (assuming you're in salt water) ? I believe the labs that do oil analysis do coolant as well.

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I'm going to have my Cat mechanic come out and check it. He just responded and said it might be the fuel transfer pump or injectors.

I may send off some coolant for analysis as I'll probably get the report before my mechanic can come out. That will help with his determination.

RickyD said:

I'm going to have my Cat mechanic come out and check it. He just responded and said it might be the fuel transfer pump or injectors.

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Interesting possibilities, I look forward to hearing what ends up being the culprit

With a Cat 3208 I don’t see how you would get diesel in the coolant. Now with a blown head gasket, something 3208’s are famous for when over heated, you would most certainly get hydrocarbons, exhaust gasses, into the coolant and this would over flow the system.

Now I can think of some creative ways that diesel would end up in the coolant but it would take a combination of severe failures.

Was this engine severely overheated?

Does the engine have a domestic water heater with heat exchanger connected to the engine. Friend of mine had the heat exchanger fail on his water heater. The pressure water system pushed domestic water into the water heater, through the heat exchanger, into the freshwater coolant loop, and out the radiator cap.

Best to eliminate as many possibilities as possible.

Ted

Do you have an engine driven mechanical fuel lift pump?
I had the same problem with a lift pump. It was working but had gaskets leaking into a coolant passage.

fgarriso said:

Do you have an engine driven mechanical fuel lift pump?
I had the same problem with a lift pump. It was working but had gaskets leaking into a coolant passage.

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This is the most likely source. Engine has not been overheated. 1750 rpm’s my normal run speed as I get a gallon a mile fuel economy at 10 knots

To my knowledge the 3208 does not have a mechanical lift pump. At least not one like found on the Ford Lehman. A pump mounted on the side of the block that has gaskets keeping fuel from block galleries. The 3208 has a combined low and high pressure pump in one housing. It is mounted on top of the engine in the valley between the heads. I can't see a way for fuel to get from the pump body to the cooling galleries.

If the head gasket failed between two cylinders, like they tend to do on 3208s, the cylinders may not generate enough pressure to ignite the fuel at low RPM and that could be precisely where the raw fuel is coming from.

Mischief Managed said:

If the head gasket failed between two cylinders, like they tend to do on 3208s, the cylinders may not generate enough pressure to ignite the fuel at low RPM and that could be precisely where the raw fuel is coming from.

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If the head gasket has failed there will be hydrocarbons in the coolant. I would certainly test for hydrocarbons. This would quickly tell you if the head gasket is the culprit. Any engine can loose a head gasket at any time. While my experience says the 3208 head gasket fails from over heating, there can always be an exception. Mischief did mention a possibility, while it’s my opinion it would take more than just a failed head gasket to prevent adequate compression, it’s still a possibility. A failed head gasket coupled with a faulty injector could be a possibility as well.

Do a pressure and leak down test on the cooling system with the engine in question.
That's easy, fast, and cheep.

tiltrider1 said:

Mischief did mention a possibility, while it’s my opinion it would take more than just a failed head gasket to prevent adequate compression, it’s still a possibility. A failed head gasket coupled with a faulty injector could be a possibility as well.

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When the gasket fails between a pair of cylinders (lets say 1 and 3), instead of the air being compressed in cylinder 1 on the compression stroke, a bunch of the air just flows into cylinder 3 (and wherever else the head gasket allows the air to flow) through the burned/missing fire rings in the head gasket. When that happens, the air in cylinder 1 may not heat up enough to cause ignition when the fuel is sprayed by the cylinder 1 injector. Now you have raw fuel present in cylinder 1 and maybe some in cylinder 3. When cylinder 3 is on the compression stroke, it may push air, AND that raw fuel, back into cylinder 1 but also potentially into the cooling system through the fault in the head gasket. I hope this makes sense.

OP has a mechanic coming. Will be interesting to see what he discovers. Keep us updated.

Well I know for a fact that I have hydrocarbons in the coolant. The finger test proved that. I don't know if the light brown contamination is evidence of burned fuel in it or if would be a chemical reaction. There is no leaking in the valley between the cylinders. The engine starts immediately and seems to run perfectly but then I have not started it since I found the contamination. My mechanic was a service manager for Caterpillar for 20 years and on his own for quite sometime. He really knows these engines so I believe his fuel pump thoughts are probably correct although I don't know how that happens. The fuel pump is in the valley between the cylinders and up against the coolant tank. Maybe it is cooled by coolant? I'm not looking forward to the bill.

O C Diver said:

Does the engine have a domestic water heater with heat exchanger connected to the engine. Friend of mine had the heat exchanger fail on his water heater. The pressure water system pushed domestic water into the water heater, through the heat exchanger, into the freshwater coolant loop, and out the radiator cap.

Best to eliminate as many possibilities as possible.

Ted

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I have had this happen twice on boats I've owned, and have troubleshot it several additional times on other folks boats. Previous owners on my boats did not replace the sacrificial anode (Raritan brand water heater) and eventually the heat exchanger in the water heater failed, allowing the coolant from the engine loop to mix with the fresh water system, and vise versa. Ended up showing up as the coolant tank on the engine overflowing....

Does your engine have a fuel cooler that coolant runs thru? My cummins has a diesel cooler that is raw water fed. When there is a failure I understand that it contaminates your fuel tank with salt water. I realize this is not your situation, but maybe you have a fuel cooler that has coolant. Or maybe no cooler. Just something to check.

fgarriso said:

Do you have an engine driven mechanical fuel lift pump?
I had the same problem with a lift pump. It was working but had gaskets leaking into a coolant passage.

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This is what my mechanic suspects. He says he can come out in November but he has not given me a date yet.

Ok, update. After initial conversation with my mechanic where he seemed to accept that there was diesel in the coolant, he called back and said there was no way diesel got in the coolant tank on a 3208 engine. That would only be possible on some very new engines like common rail but not my 1990 3208. So I sent samples out for lab inspection. In the meantime, I figured I'm getting sea water into my tank through a failed heat exchanger and the fact that my coolant is red, made me think it was diesel. The coolant tank has overflowed so I know now sea water is getting in. Lab results have not come back yet but I have already removed the heat exchanger and purchased a new one. Yipes, very pricy. Why buy new and not repair the old one? Well I had to hire my A/C guy to come and move my A/C compressor so I can slide the port engine heat exchanger out. Then I have to hire him to come back and reinstall and recharge at some expense. The starboard engine is easy as it would slide out to the center with not obstructions. So I'll hopefully repair the old one and save it for a possible starboard engine replacement so even if it fails again, it will be easy to exchange. Now I'm doing clean up and flushing. It must have been doing this for some time as there is a substantial amount of rust coming out. So far I have just poured in about 4 gallons of water and drained it out and it still is coming out looking like something that belongs in the toilet after binging in Mexico with a sensitive stomach. No offense intended as I love Mexican food.

I plan to rinse the engine as best I can, then add some flush chemistry and run with fresh water. Rinse again before recharging with coolant. Cat coolant is not cheap and I'll need 8-10 gallons. Any other suggestions from the Group?

Do you have the Cat manuals? Mine tell about options to Cat coolants. I'm not at the boat for a few days so working from memory. I'm running a more run of the mill coolant rated for diesels. The main thing I have to pay attention to is to change and flush more often than with Cat coolant.

Right, I do have the manuals. Not sure how complete they are. When in doubt I use the manufacturer's recommended stuff.

Your 3208 should have two axillary ports, commonly used for water heaters. Attach a hose to these two ports and lead them to a 5 gal bucket. One hose attach a pump powered by a drill motor. The other hose attach a filter. Fill the bucket up with water and start flushing. After things clean up change from water to coolant and flush some more.

When you are all done do a pressure check on the system. This would rule out any head gasket worries. I suspect you have found your problem but its always good to rule out catastrophic possibilities.

Just thinking out loud and spitballing but what does your exhaust look like ? Is it whitish from steam. The two giveaways on head gaskets is normally coolant steam in the exhaust stream and pressure in the coolant tank. If coolant is in fact washing down the cylinder walls then incomplete fuel combustion is likely resulting in unburned fuel. This coolant and fuel mix can wash down past rings into your oil. If the condition has been going on a while and you’ve got some overheated cylinders then you’re rings may be toast and wash down even worse. A good analysis can provided percentages. I guess the inverse may be possible where unburned fuel is forced back into the water passages past the bad head gasket but this is a wild ass guess.