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Discussion Starter · #1 ·
Every time I think I’m done with any issues, something else happens. I’ve got close to 15000 miles on a complete rebuild on my 4bt. Driving down the highway around 60 to 65 mph at 2000 to 2200 rpm’s and it started to overflow the radiator reservoir. It never ran hotter than 180 to 185 deg.. After it cooled down the radiator was full and I didn’t add any coolant. Worked ok for a couple of weeks and puked just a little. It was foaming in the radiator with the cap off and was about 4 “ below the top when I checked it later. The thermostat was cycling as was the electric fan. Sending unit for fan at rear of head drivers side, 190 deg on I believe. Block test got hydro carbons inconclusive. So thinking and hoping I’ve just got an air bubble and steam causing my issues. Ran it up on ramps and let it idle with the radiator cap off and kept topping off the radiator. It settled down and I drove it for 40 miles (2 different times about 20 miles each time). The reservoir had about 2 inches of fluid and stayed there over night. Then the last time I drove it it filled the reservoir to almost overflowing. It sucked the reservoir down to where it was at 2 inches over night. While all this is going on the temp after warming up will stay right at 180 deg, most of the time. Sometimes it won’t go over 165 at road speed until I slow down for town or country cruises. What would cause it to not warm up until I slow down? If I override the fan and let it run constantly it doesn’t want to get over 160 deg. Thermostat? Radiator cap? I sent a sample of fluid in for an analysis.
 

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... I don't even run a fan on mine & Most of the time It's at about 160 to 185. after running fro 30 minutes & I'm moving 20 mph.
I do have an electric fan. & If I forget & leave it on mine will go down to about 120 or maybe 130
Unless it's 105 put side.
...
I'm Not sure about yours . Just adding my Tid Bits so I CAN SEE IF SOMEONE GIVES YOU some information.
GOOD luck.
 

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I would start with the thermostat, get a good quality thermo, sounds like the thermo might be sticking, it should close below 180 if that's what it's rated for, the difference between 165 and 180 is really with the proper range, your sending unit will pick up changes rapidly because coolant temp changes rapidly, more so than say oil temp, also an oil temp gauge is a good thing to have especially on a diesel motor, gives you a truer reading of how the motor if functioning heat wise. On your coolant puking issue, do you have a remote reservoir to capture coolant overflow? also what type of cap are you running? buy a quality cap with at least 15 lb psi rating, so if you running a closed system and your water pump is not leaking, cap is good, when coolant cools it should draw back into radiator, then all you have to do is monitor your coolant level at the remote reservoir. You could do the overnite cool down check, if you have pressure when you open the system, it could be ahead gasket issue, you shouldn't have any pressure if the system is functioning properly.
 

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Your temp ranges sound very normal for a 4bt. It is a very efficient engine heat wise. Sometimes hard to get it to heat up at normal cruising speed unless it's under load. Standard thermostats are set for 83 deg C or 181.4 deg F. With that many miles since the rebuild the air in the coolant would make me suspect a blown head gasket. Any residual air should have long ago worked out of the system. Have you checked the oil to see if there's any leakage into that system? If none, then the lost coolant is likely going out the exhaust system.
 

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if you have a pressure tester put it on the radiator when running and see if it builds pressure. also pressure up the system and look for coolant everywhere. the foaming in the radiator comment makes me wonder.
 

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Discussion Starter · #6 ·
Ok to begin with, yes I have an overflow reservoir (empty Jack Daniels bottle) how it got empty I don’t remember. The fan switch is 185 on 175 off. The foaming quit when I got the system topped off. Like Charlie I suspect a head gasket, except why isn’t it doing it all the time? And I’m not getting any water in the oil nor is there any noticeable water out the exhaust like white smoke or condensation. As far as the thermostat why won’t it keep it at 180 deg with the fan running constantly at idle. It will stay right on 180 doing 60 down the highway. If it closes it should build heat regardless of fan operation shouldn’t it? The fan never kicks on when running down the road, only after extended idling or when the a/c is on. No pressure in the system overnight, vacs the overflow out of reservoir back into radiator. I’m thinking thermostat or a head gasket but again why wouldn’t a head gasket be a constant problem? The pressure I feel in the upper radiator hose when running builds until the stat opens. If it’s the thermostat would it be a constant or intermittent problem. So far the only TRUE CONSTANT is the pain in my ass this thing gives me from time to time. One more thing, im running NAPA green antifreeze. It says it’s safe for aluminum radiators but a diesel mechanic says I should be using NAPA red. I await the analysis from the lab as to hydro carbons in the antifreeze.
 

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Has this only happened once?
If it happens again see if the radiator hoses are hard or has it lost pressure. Possibility it is a dodgy radiator cap not holding pressure and allowing more fluid to go to the overflow bottle.
 

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Cummins oem thermostat. I tried various others, they just don't work correctly. Only downside is it struggles to get over 165 in winter without blocking the rad...even then
 

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Sort of off topic but it sounds like your gearing is wrong for a 4B. It would be way happier at less than 2K rpm continuous.
No idea what your Curb weight is but my Tahoe is about 6500lbs and feels great with its gearing that runs about 1700 at 65. These engines make torque at modest revs and its best to take advantage of that.
 

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Ok to begin with, yes I have an overflow reservoir (empty Jack Daniels bottle) how it got empty I don’t remember. The fan switch is 185 on 175 off. The foaming quit when I got the system topped off. Like Charlie I suspect a head gasket, except why isn’t it doing it all the time? And I’m not getting any water in the oil nor is there any noticeable water out the exhaust like white smoke or condensation. As far as the thermostat why won’t it keep it at 180 deg with the fan running constantly at idle. It will stay right on 180 doing 60 down the highway. If it closes it should build heat regardless of fan operation shouldn’t it? The fan never kicks on when running down the road, only after extended idling or when the a/c is on. No pressure in the system overnight, vacs the overflow out of reservoir back into radiator. I’m thinking thermostat or a head gasket but again why wouldn’t a head gasket be a constant problem? The pressure I feel in the upper radiator hose when running builds until the stat opens. If it’s the thermostat would it be a constant or intermittent problem. So far the only TRUE CONSTANT is the pain in my ass this thing gives me from time to time. One more thing, im running NAPA green antifreeze. It says it’s safe for aluminum radiators but a diesel mechanic says I should be using NAPA red. I await the analysis from the lab as to hydro carbons in the antifreeze.


where to start: Start with the overflow draw tube in your whiskey bottle.. if it can move and doesn't sit on the bottom .. it might be drawing air into the system... next,, you may have an air lear around a hose clamp retighten all clamps .. or any mod you made to built tubing to your radiator... your radiator hose could have a pin hole lead.. your heater hoses could have the same problems... you could have a small leak in your heater core.. Your water pump could be sucking air thru the seal.. ( you can have air leaks that don't leak antifreeze out) or you may have a foreign body floating in your cooling jacket causing hot spots in you block which create steam and cause this problem.. . you start by running a 24 hour pressure test... let it cool down totally.. top it off... put the pressure tester on the radiator and pump it up to 14 pounds.. and let it sit until it starts dropping ( then look for leaks including at you heater core) or over night... and if that doesn't show anything.. post a reply to me and i'll go through the next tests.. .. but i can tell you it isn't worth your time or money to throw parts at the problem till you know the problem..
 

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Discussion Starter · #13 ·
Sort of off topic but it sounds like your gearing is wrong for a 4B. It would be way happier at less than 2K rpm continuous.
No idea what your Curb weight is but my Tahoe is about 6500lbs and feels great with its gearing that runs about 1700 at 65. These engines make torque at modest revs and its best to take advantage of that.
Yeah I’m geared pretty low 4:11. The 4l80e works great to keep the rpm in the 2000 range at higher speeds. A 1958 Willys isn’t very aerodynamic at any speed over 60. I don’t drive it much over that. I know it would be happier with taller gears or even bigger tires (but that ain’t gonna happen cause 32.5’s is about all my old legs will handle crawling in the cab). It gets 18 plus mpg average and I’m ok with that.
 

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Discussion Starter · #14 ·
where to start: Start with the overflow draw tube in your whiskey bottle.. if it can move and doesn't sit on the bottom .. it might be drawing air into the system... next,, you may have an air lear around a hose clamp retighten all clamps .. or any mod you made to built tubing to your radiator... your radiator hose could have a pin hole lead.. your heater hoses could have the same problems... you could have a small leak in your heater core.. Your water pump could be sucking air thru the seal.. ( you can have air leaks that don't leak antifreeze out) or you may have a foreign body floating in your cooling jacket causing hot spots in you block which create steam and cause this problem.. . you start by running a 24 hour pressure test... let it cool down totally.. top it off... put the pressure tester on the radiator and pump it up to 14 pounds.. and let it sit until it starts dropping ( then look for leaks including at you heater core) or over night... and if that doesn't show anything.. post a reply to me and i'll go through the next tests.. .. but i can tell you it isn't worth your time or money to throw parts at the problem till you know the problem..
From one old guy to another THANK YOU! The damned thing has been working fine ever since I burped it on the ramps. But it worked fine for 15000 miles before it threw a fit so who knows. The tube in the reservoir does go all the way to the bottom. I know I have a small seep in the lower water intake that I fabed up years ago. It isn’t much, evaporates before it ever drips. I’ve got a new heater core and a/c system (Vintage Air). The heater is very touchy to adjust which could be an indication of air in the system. I haven’t needed it since I burped it. I like your idea of the pressure test. I’ll hunt up a pump and give that a try.
 

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From one old guy to another THANK YOU! The damned thing has been working fine ever since I burped it on the ramps. But it worked fine for 15000 miles before it threw a fit so who knows. The tube in the reservoir does go all the way to the bottom. I know I have a small seep in the lower water intake that I fabed up years ago. It isn’t much, evaporates before it ever drips. I’ve got a new heater core and a/c system (Vintage Air). The heater is very touchy to adjust which could be an indication of air in the system. I haven’t needed it since I burped it. I like your idea of the pressure test. I’ll hunt up a pump and give that a try.
I think you have identified the problem ...a small leak or pin hole and air will enter the system and build up over time and then you get the cold reaction when you water pump starts cavitating ( frothing at the mouth so to speak) from an air build up in the system.. so you are on the right track.. if you test and fix your known leak... Hope this helps.. if not then it gets uglier.. diesels don't tend to test well on the chemical test ( blue to gerrn fluid bulb test ( or is it yello? I don't remember).. if the pressure test and fixing the known leak doesn't work.. there are labs that test antifreeze for carbon compounds... and that is likely the next step.. but I think your know leak is the most likely culprit..
 

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Discussion Starter · #16 ·
I think you have identified the problem ...a small leak or pin hole and air will enter the system and build up over time and then you get the cold reaction when you water pump starts cavitating ( frothing at the mouth so to speak) from an air build up in the system.. so you are on the right track.. if you test and fix your known leak... Hope this helps.. if not then it gets uglier.. diesels don't tend to test well on the chemical test ( blue to gerrn fluid bulb test ( or is it yello? I don't remember).. if the pressure test and fixing the known leak doesn't work.. there are labs that test antifreeze for carbon compounds... and that is likely the next step.. but I think your know leak is the most likely culprit..
I’ve already got a sample of the antifreeze sent off for analysis. However my buddy at the truck shop says he doesn’t trust the labs. The blue dye in the block test kit is supposed to turn greenish yellow. I took 2 white plastic cups and put test fluid in one and untested fluid in the other. The difference was practically nil. For one thing when I did the test it was foaming and steaming to some extent. (Before I burped it).
 

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I’ve already got a sample of the antifreeze sent off for analysis. However my buddy at the truck shop says he doesn’t trust the labs. The blue dye in the block test kit is supposed to turn greenish yellow. I took 2 white plastic cups and put test fluid in one and untested fluid in the other. The difference was practically nil. For one thing when I did the test it was foaming and steaming to some extent. (Before I burped it).
so any news?
 

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Discussion Starter · #18 · (Edited)
Analysis hasn’t returned yet. Last night I got a pump and pressurized the system. Haven’t checked it yet this morning. It’s been working fine until 2 days ago. The overflow level has been steady at about 4 inches hot and 2 inches cold. Then it went to about 6 inches constant. I put a new hose on the recovery line after I found what I thought was a cut in the old one (it wasn’t). The pump I borrowed has an adapter to check the cap. I’ll do that after the pressure test. Probably should have done that first.
 

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Discussion Starter · #19 ·
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?
 

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the thermostat will stay open after shut down if the temp is hot enough and you will get flow thru the radiator even if its not running. the draw back happens when it cools down and creates a vacuum in the system to draw the coolant back in. the pressure rating on your cap determines how and when coolant goes to the overflow bottle. if its high enough it probably wont vent but that's harder on the system components.
 
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