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After pressurizing the system to 15 lbs overnight it had bled down to about 10 to 12 lbs this morning. I had three leaks showing. Two are so minute they didn’t drip onto the floor. One is the seepage through the lower water inlet where I fabricated it and the other was where the the lower water inlet bolts to the front side of the block around the rubber sleeve gasket. The main leak (and it made a puddle on the floor) was around he lower radiator hose clamp at the radiator neck. It was the easiest fix. The radiator cap tested fine. So I’m guessing depending on where the thermostat is when I shut it off it makes a difference whether it sucks fluid out of the overflow container or air through the places where it’s leaking?
Nope It sucks fluid the easy way.. from the radiator hose that isn't restricted.. those leaks may well have been your problem as i surmised they would exist.. please let us know... thanks
 

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Discussion Starter · #22 ·
Ok here it is. The first pressure test leaked down to 11 lbs over night and I found three small leaks at hose clamps and one very small seep through the lower water inlet where it was brazed and soldered. I needed to replace the exhaust manifold gaskets and while I was at it I pulled the lower water inlet (which in my case necessitates removing the a/c bracket). I put a new rubber gasket in the lower inlet when I put it all back together but after running it, it had a small leak so I pulled it apart and put some sealer around it and got that stopped. I pressurized it last night and this morning it was at zero but no obvious signs of leakage,😩. So I’ve either got a leak internally or somewhere where I have an air bubble in the system. No sign of of water in the oil or out the exhaust and no overheating before this started. So right now I’m going to run it and keep an eye on things and see what happens before I tear into the top end.
 

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This thing is getting weird. First test leaked down some, but after fixing those small leaks it leaked down to zero on the next test. Did the coolant level in the radiator drop any on the second test? If not, then is could have been air but where the heck is it getting out. If the coolant level dropped then you have an internal engine leak. I'd watch the oil pan for increase in oil level. Remember that oil floats on water so there could be coolant in the bottom of the pan. Since the engine is mainly a closed system except for the draft tube, might stick a balloon on the hose and see if it inflates any. Only other way out would be an open intake or exhaust valve.
 

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Discussion Starter · #24 ·
I drove to town after putting it all back together and making sure I had all the air bled off. It worked great as far as temperature with it staying right at 180 deg plus or minus 2 or 3 deg. Got home looked underneath and there’s a leak. I thought it it was the lower intake connection as it looked like it was the culprit earlier. It had a new rubber square o ring and I used gray gasket sealer the next time and thought it was fixed. Hard to tell where it was coming from exactly but thought it was the lower water inlet. So this time I pulled the water inlet and the water pump. I couldn’t see where the inlet had been leaking but the water pump may be the problem. The weep hole was full of wet rusty sludge and if it was dripping down on the water inlet it may have fooled me. Pump only has about 16000 miles and it’s easy enough to replace. I’ll get one tomorrow and seal everything up good. One thing has improved for sure and that’s how quick I can get it apart 😝.
 

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Discussion Starter · #25 ·
This thing is getting weird. First test leaked down some, but after fixing those small leaks it leaked down to zero on the next test. Did the coolant level in the radiator drop any on the second test? If not, then is could have been air but where the heck is it getting out. If the coolant level dropped then you have an internal engine leak. I'd watch the oil pan for increase in oil level. Remember that oil floats on water so there could be coolant in the bottom of the pan. Since the engine is mainly a closed system except for the draft tube, might stick a balloon on the hose and see if it inflates any. Only other way out would be an open intake or exhaust valve.
I think I may have finally figured it out. The last time I said I pressurized the system and it bled down to 0 with no sign of leakage I had only filled the system to get the level up to fill the lower water inlet because that’s where I thought the leak was. I didn’t fill it high enough to fill the water pump. New water pump, all back together and so far no leaks. I’ve driven it but haven’t pressure tested it. The old pump was a “genuine” Cummins made in India. New pump is from NAPA. No telling where it’s made. Only difference is the impeller design.
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Discussion Starter · #27 ·
I’m beginning to think I’ve never had the system completely purged of air. It’s working great now. Held 16 lbs of pressure with no leaks. I’ve got a 16 lb cap and wondering if that much is necessary.
 

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Cummins spec 7 and 15 lb cooling systems if I remember correctly, it is it the manual.
 

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Discussion Starter · #29 ·
I found this on a post from sometime back.
Pressure Cap 220 degree systems B3.9 Engine 15 PSI
Pressure Cap 210 degree systems B3.9 Engine 7 PSI
That’s a big difference for 10 degrees. I’m running around 180.
 

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I’m beginning to think I’ve never had the system completely purged of air. It’s working great now. Held 16 lbs of pressure with no leaks. I’ve got a 16 lb cap and wondering if that much is necessary.
likely not... a chased a subaru for a year.. it would start puking.. but not be hot... the heater core was bad enough to allow air in but not bad enough to leak.. like lit had flap on it on the inside..
 

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Discussion Starter · #32 ·
It now has a 7 lb cap and I ran it for about 60 miles this afternoon back roads and highway. Ambient temp around 80 deg and was running the a/c. With electric fan running all the time with the a/c on it ran about 170 deg. constantly. NO LEAKS!!
 

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Higher pressure caps delay the boiling point of water. With 15psi you gain almost 20C in boiling point (over 0psi).
Of course that means if it boils it spits out straight steam!

I had a line from thermostat housing to (pressurised) overflow bottle spring a pin-hole leak many years ago after pushing my 4BD1T pretty hard up a ski-field road. It was spraying out steam like special effects in a bad movie!
 

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I agree with what Whiskey welder said.
Back when I had my parts store We told customers that . FOR each pound of pressure You gained 1 1/2 degree before BOILING.
 

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Discussion Starter · #36 ·
So I’ve got over 300 miles on this thing since I “thought” I had the problem fixed. Drove it yesterday for about 20 miles with the ac on (ambient temp about 92). Temp holding fairly steady around 180 deg.. I’ve noticed it going up to around 190 on several different occasions but never any higher. It’s been syphoning the reservoir when it cools. Life is good, until this morning. Started it up in the shop after making sure the fluids were where they should be and backed over to the house to pick up my wife. She says something is running out underneath. I say it’s the ac. She says it’s REALLY running out. I say it’s the ac. She says I better look. Hell it’s antifreeze! Pop the hood and the reservoir is spewing like a geyser. It hasn’t even had time to warm up. It’s ran for maybe 2 minutes. So whatever my demon has been, it’s finally turned loose. I’m wondering if it isn’t a broken head bolt to fail that completely that fast. When I pulled back to shop I could see where it puked as I backed out. Must have failed after it cooled down from the day before.
Tire Wheel Land vehicle Vehicle Car

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Before you take the head off and have it pressure checked.... try this trick.. disconnect the heater core hoses.. and hook them in a loop bypassing the heater core... I'd say your temp fluctuation are normal... the temp rises... the thermostat opens.. the guage falls because the cooling system is doing its job... there is the possibility you have a blockage in the block/coolant system... like a soft ( freeze) plug that was pushed in and left in the block acting as a gate at times... i have seen that with the alumunum off a coolant bottle.. or a large rust chip ..or a hose that was Bad on the inside but didn't show it on the out side... where a rubber flap will block flow..

did you get the report back on coolant sent to be tested???.. unfortunately I am thinking it is a cracked head.. but before you do that.. try my trick..
 

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So I’ve got over 300 miles on this thing since I “thought” I had the problem fixed. Drove it yesterday for about 20 miles with the ac on (ambient temp about 92). Temp holding fairly steady around 180 deg.. I’ve noticed it going up to around 190 on several different occasions but never any higher. It’s been syphoning the reservoir when it cools. Life is good, until this morning. Started it up in the shop after making sure the fluids were where they should be and backed over to the house to pick up my wife. She says something is running out underneath. I say it’s the ac. She says it’s REALLY running out. I say it’s the ac. She says I better look. Hell it’s antifreeze! Pop the hood and the reservoir is spewing like a geyser. It hasn’t even had time to warm up. It’s ran for maybe 2 minutes. So whatever my demon has been, it’s finally turned loose. I’m wondering if it isn’t a broken head bolt to fail that completely that fast. When I pulled back to shop I could see where it puked as I backed out. Must have failed after it cooled down from the day before. View attachment 133829
View attachment 133828
and now for a funky thought... when you routed your serpentine belt... did you check it was so the water pump turns the correct direction?
 

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Discussion Starter · #40 · (Edited)
and now for a funky thought... when you routed your serpentine belt... did you check it was so the water pump turns the correct direction?
Before you take the head off and have it pressure checked.... try this trick.. disconnect the heater core hoses.. and hook them in a loop bypassing the heater core... I'd say your temp fluctuation are normal... the temp rises... the thermostat opens.. the guage falls because the cooling system is doing its job... there is the possibility you have a blockage in the block/coolant system... like a soft ( freeze) plug that was pushed in and left in the block acting as a gate at times... i have seen that with the alumunum off a coolant bottle.. or a large rust chip ..or a hose that was Bad on the inside but didn't show it on the out side... where a rubber flap will block flow..

did you get the report back on coolant sent to be tested???.. unfortunately I am thinking it is a cracked head.. but before you do that.. try my trick..
The heater has a valve that shuts the flow off so I don’t think looping the hoses will help. But you brought up an interesting question. Collapsed hoses is something I’m going to check. And after all the shtf this morning, I drove it back to the shop (100ft) and it was puking all the way. I drained the antifreeze and started it to drive inside and had no pressure at the radiator cap. Fluid or not, if pressure was getting in the coolant system it should still have been venting at the cap. I didn’t let it run very long without coolant but tomorrow morning I’m driving it up on ramps and filling the system and see what happens. If it doesn’t puke I’ll pressure test it again. I can’t figure out why it was fine and then failed completely overnight. 16000 miles and now this. Your suggestion about a blocked coolant passage makes me wonder as well but why would it do it when it’s cold? Shouldn’t be circulating fully until the thermostat opens.And I’m pretty sure after 16000 miles the belt is routed on the water pump correctly. Im updating this reply this morning. It dawned on me last night that looping the heater hoses could possibly act as a bypass for the water pump. Is that where you going with the suggestion? And brings up another question, how does a 4bt bypass until the thermostat opens? Updating again, I found this
Organism Font Line Parallel Rectangle
so maybe I’ll check the area under the thermostat to see if I’ve some blockage. The fact that no pressure built up even for the short time I ran it with no fluid makes me wonder. One thing for sure Kansas is HOT right now!
 
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