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Losing a lot of coolant

Losing coolant in my 2002 Pete 387 Cat C-15 6NZ with 975k miles on it. Lost about 4 gallons in 300 miles. Truck has never lost coolant prior to

-No visible leaks under truck

-no evidence of it coming out of the stacks (no smoke or water)

-just got oil sample back and sample is perfect

Any ideas of where it is going?

Thanks,

Steve

Answer this question I have this problem too

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1.Have you had any recent repairs done to the cooling system or engine in general?

2.Can you pull over with the engine hot and see any cooling squirting out of the overflow tube?

3. Any smoke at start-up? I mean somebody holding their head right next to the stack and then watching/smelling the exhaust as you fire it up.

4. How long have you owned the truck and how many miles are on the engine?

I've seen engines burn large amounts of coolant and you would never know it by looking at or into the stacks. It usually does not show up. I've also seen engines burn large amounts of coolant without the slightest indication of any sodium/potassium in the engine oil also. I have a few theories on this but they don't really matter. 4 gallons in 300 miles is a lot.

1. Do the above test with a bottle to see if it is in fact going out the overflow hose. Usually the bottom of the truck will have coolant all over it too.

2. The next thing I like to do is disconnect/block off every external source of coolant flow to/from the engine. Shut off heater lines. I have taken the air compressor completely off and installed a block off plate before. You just want to isolate the problem to either the engine or the truck so you're not wasting time, chasing ghosts.

Once you completely isolate the engine from everything but the radiator, I verify if it actually is combustion gas by making a home made radiator cap (I used an adapter from an old cooling system pressure tester) with a manual pressure release valve on it and a 15-20 lb pressure gauge. Run the engine to operating temp-bleeding off the air pressure about 4 times to remove the natural pressure formed from coolant expansion- then see how high the gauge will go (Don't go much above 15 psi or hoses may start blowing). If the gauge keeps rising after bleeding it off after about 4 times, you will have 100% confidence that combustion is leaking into the cooling system and coolant is probably being sucked back into the cylinder on the intake stroke.

This leads to tearing into the engine.

These problems, I've found, are usually never easy to find.

What I usually do next is pressurize the radiator (with the engine cool) to about 10 psi, then remove the oil pan, all 6 injectors, and any cover on the front of the engine and search for the coolant leak with a high quality borescope. Even if it takes all day, a good, detailed search will usually locate the coolant and then maybe lead to your problem.

Almost every time I've seen this happen on a Caterpillar, and everything else externally has been checked/changed, I remove the head and carefully inspect all 6 fire-rings on the old head gasket. The fire ring is the solid metal ring on the inside of each of the 6 circles. (A lot of shops pitch the old gasket without inspecting it). There will be a small black "soot" mark usually about 1/16" inch in one or two corners of one, two or three fire rings. That soot is where the combustion is leaking into the cooling system. (If that's the problem). It will at least lead you to inspect that particular spot on the deck or head for abnormalities or warping.

Head gaskets usually only blow when the engine gets very hot (the metals expand), or the liners slowly fall down into the cylinder block (usually higher mileage). If the shop says you have a blown head gasket, yet you never overheated the engine, MAKE SURE they check the "liner-protrusion" when the cylinder head is removed.

Give us an update and I hope this helps a little.

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Thanks Jeff,

I recently had charge air cooler, crankshaft balancer and damper done right before this problem but can't imagine any would be related to coolant issue.

I've had the truck for 3 years it now has 975k on it

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Start by presurizing the system and verify no external leaks if not I would suggest modifying a water bottle so your coolant overflow hose will slide in through the cap snugly leaving about an inch between the hose end and the bottom of the bottle fill the bottle 3/4 full of water and run the truck through a heat cycle starting cold all the way to fan on temp 212 or so changing engine speeds from idle to high idle observe the bottle watch for a steady constant stream of bubbles if you do see the bubbles you most likely have a head gasket problem or top liner seal issue PS do this test with a new radiator cap installed

Update

I wouldn't say as a rule you would see it in the oil. It is very possible to just get compression in the cooling system which would push the coolant out the overflow. Since the 3406 family of engines use a complex block to head seal consisting of a steel gasket a spacer plate a standard style head gasket a series of rubber coolant and oil seals and rubber upper liner seals symptoms can vary. Cat also had some problems with liner protrusion being inadequate allowing liners to move causing all kinds of good stuff. By all means start simple change the rad cap drain and check air tanks for coolant any aux systems with coolant ie Tri PAC fuel fired coolant heaters fuel tank heaters trans oil(water cooled models) etc. a bottle test is cheap and easy if nothing shows up

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We pressure tested and ran around 10 lbs pressure.

With head gasket wouldnt coolant show up in oil

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ck 4 tubes in fuel tanks the heaters run hot coolant in and back 2 eng leaks all the time

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So then the coolant is in the fuel tank and you "burn it" slowly?

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Should I take a fuel sample to see if coolant is in the fuel?

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You wouldn't need to do a fuel sample to see if it's your tank heaters leaking. If you have shut off valves on your tank heaters you could just turn them off a while and see if you still consume coolant.

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I wish I could help you with this problem it's annoying. If and when you find the problem let me know I have similar problem on a Detroit Series 60 that nobody can find. I have no antifreeze in the oil and no leaks no tank heaters and no air supply that goes to the heating system no antifreeze in the air tanks no combustion gases in the antifreeze but I still lose coolant.

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That is a great reply/answer Mel!

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Mechanic says I do not have tank heaters on my truck.

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ck rear heater core will leak out under bunk vent tube

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Hi, coolant in diesel is mixed in engine and go through diesel return line , you should get diesel checked.

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Steve Conjerti will be eternally grateful.
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