763 drains coolant thru top of overflow bottle

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Wallaman

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Aug 13, 2022
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6
I have a 2000 763G bobcat that drains coolant from radiator through top of overflow reservoir.
What would be causing this and what are things to check? It has the original radiator cap that I have cleaned.nnIt mis a 13 lb. cap.
 

foton

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Mar 1, 2018
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there should be two lines marked on the overflow tank a min. and max. level so your coolant should be between the two. are you overfilled? and verify the pounds required on the rad. cap and replace with recomended cap do not go higher to prevent overflow.
 

brdgbldr

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Jun 1, 2012
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First thing that comes to mind is that the overflow reservoir is too full. The fluid level should be at the bottom line when cold and only reach the top line when fully heated up.

If that is not the case, you could have air in the system. This seems unlikely though. An air pocket will expand much more than fluid.

Have you replaced the antifreeze at all? Antifreeze has a life span and also, if the mixture is incorrect you could have too much water in it and it will boil causing all sorts of problems. Too little water can also cause problems. I always use the pre-mixed to avoid any issues. If you mix it yourself you are supposed to use distilled water. Contaminants, like chlorine and minerals in the water, are not good for the system.

You may want to replace that radiator cap. The springs in them do fail over time.
 
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Wallaman

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foton and brdgbldr: Thanks to both of you for your responses. I did change the antifreeze coolant about two months ago. I got the antifreeze from NAPA that was designated for a diesel engine. I did not however use distilled water. I use an empty gallon container to mix a 50/50 solution. As far as air in the system, I know nothing about that. I always have the coolant level in the overflow reservoir at the minimum level line when cold. My wife went to town and bought me a new cap while I was spraying weeds today. I put it on to make sure it fit but so far have not started it up. I will tomorrow. Maybe....... the original cap was 13 lb. I told her to get a 16 lb cap. That was before I read these posts. Will a 16 lb. cap cause problems? Thank you.
 

brdgbldr

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Your cap should be 13psi. Adding an extra 3 psi to a hose could cause it to burst. You may also find any other weak spots in the cooling system.

Are you sure that the new antifreeze wasn't already mixed?

You can test the antifreeze just make sure you have the correct tester for the type of antifreeze you are using. If a lot of antifreeze is coming out of the overflow, the most likely cause is boiling.
 
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Wallaman

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Aug 13, 2022
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brdgbldr: Hi. The coolant was heavy duty NAPA concentrate. I put a new 13 lb. cap on with same results. I then bought a 16 lb. cap and put it on. With that cap on, and the coolant in reservoir at minimum level cold temperature, running the unit for 6 straight hours, the coolant level in overflow stayed the same but radiator was down 3/4 gallon. There is coolant leakage on right side of engine, behind/above oil fill tube. Didn't have chance to check it out as it was raining like a holstein pissing on a flat rock. As I was typing this I was trying to picture in my mind... if there was radiator hose up there and perhaps a loose clamp or small hole????? Is there a faint possibility the new 13 lb. cap was defective? Thank you sir.
 

brdgbldr

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It is always possible that a new part is defective. I could tell you stories….

Have you looked at the thermostat? I don't know why I didn't think of this earlier. A bad thermostat can cause all sorts of problems with overheating.

The coolant in the overflow should rise when warmed up. If it did not, then the radiator cap is not lifting as it should. This can be caused by either a too high pressure cap or a leak in pressure somewhere else in the system. The problem with using the higher pressure cap is that if there is a weak spot in the system the fluid will come out there instead of the overflow tank.

I would try to stick with the recommended cap and fix any leaks that you have. There is a radiator hose on both the left and right side of the radiator. There is also probably a small coolant return hose on the thermostat housing.

At this point keep checking that there isn't any antifreeze in the engine oil. A blown head gasket, rarely, can put pressure into the coolant system. Also, when running, pay attention to the exhaust. Just a precaution.
 
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Wallaman

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Aug 13, 2022
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6
It is always possible that a new part is defective. I could tell you stories….

Have you looked at the thermostat? I don't know why I didn't think of this earlier. A bad thermostat can cause all sorts of problems with overheating.

The coolant in the overflow should rise when warmed up. If it did not, then the radiator cap is not lifting as it should. This can be caused by either a too high pressure cap or a leak in pressure somewhere else in the system. The problem with using the higher pressure cap is that if there is a weak spot in the system the fluid will come out there instead of the overflow tank.

I would try to stick with the recommended cap and fix any leaks that you have. There is a radiator hose on both the left and right side of the radiator. There is also probably a small coolant return hose on the thermostat housing.

At this point keep checking that there isn't any antifreeze in the engine oil. A blown head gasket, rarely, can put pressure into the coolant system. Also, when running, pay attention to the exhaust. Just a precaution.
Hi brdgbldr. I will check the thermostat tomorrow. First thing in the morning I am going to go get a 13 lb. cap at NAPA. The small hose on the thermostat looks like it has some fraying or something going on with the outside of it. I am going to see if I can get that new hose tomorrow. I will look for difference in exhaust. I looked at engine oil on dipstick tonight after running and didn't see any bubbles..... Thank you so much for responding to my posts/problems.
 

oiu789

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Dec 23, 2017
Messages
138
I hope not but it could be a compression leak ie bad head gasket, cracked head or block. I had a engine with dry sleeves it had a corrosion hole in one cylinder thru the block and liner. Check for bumbles in the over flow tank. Fill the tank to the top and run it if it starts over flowing right away be fore heating up thats a good bet that compression is blowing the fluid out.
 

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