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Discussion Starter · #1 ·
Hi all, new member to site but long time reader and looking forward to the conversations.

We currently have the old 8640 in the shop and are trying to figure out why there is coolant pushing out of the overflow line. The tractor is our secondary tractor and has just rolled over 10,000 hours of which I have owned for less than 1000 hrs and do not know any history before that.

The first symptoms of an issue were that there was no heat in the cab and coolant would push out of the overflow line and random intervals when pushing snow (has a 14ft blade on it). The first thing we did was drain all the coolant and change the 3 thermostats to make sure one of them wasn't staying open. We fired it up after putting it back together and had coolant pushing out of the overflow. Installed a pressure gauge on top of rad to verify rad cap was cracking at proper pressure at it was around 11 psi (has been converted to the 10 psi system from the original 15 psi). However, would not hold pressure when shutdown so we replaced the cap anyways so now it holds for hours after shutdown. Ran the tractor for 5-6 hours hoping that it was an airlock issue. Coolant did stop coming out after a while and system stayed around 8 psi and all seemed well when running. Shut tractor off and after it cooled down the coolant level was too low to see in the rad. Never added anymore coolant and started the tractor cold again and the pressure climbed over the 11 psi within 90 seconds and seems to do this every time its started and only pushes out coolant if there's enough in the rad to push out.

Then we started thinking head/head gasket issues and started looking for bubbles in the rad when running but can not see any bubbles but the coolant level rises when running and will run right out of the rad if close to full within 10-15 seconds. But if the coolant is down 4-5 inches it will only rise a couple inches then stop. So we got a tester with solution to look for combustion gas coming through the rad and got nothing. The last thing we did was pull the top rad hose off the rad and ran the tractor to try and figure out if the extra coolant coming into the rad was coming from the top or bottom rad hose. There was a small stream coming out of the top rad hose and through the thermostats somehow (cold engine) BUT as the top hose was off the level in the rad still rose like it was before. The only way to fill the rad at this point is through the bottom hose........somehow.

I should also add that at no point has the heat gauge ever got into the red but it does move and we know it works. Also, at some point in there we had split the return heater hose line to verify that it was circulating through the cab and it was but there was also pressure coming from the other side of where we split the line so don't actually know if it circulates when connected if both sides see pressure.

Our thoughts now are water pump and/or blockage of some kind but neither option makes total sense to us. There is no sign of bearing failure or leaks by the pump. Could a wrecked impeller cause this somehow? Does anyone have any other thoughts? Or tests to do? Can we be confident that tearing into the water pump is not a wasted effort?

Apologize for the novel but we are running out of thoughts.

Thanks
 

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Usually that would be a head gasket. any oil in the coolant or coolant in the oil? I ask because the oil cooler can leak causing this. IDK if it would cause what you describe.
 

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Discussion Starter · #3 ·
Usually that would be a head gasket. any oil in the coolant or coolant in the oil? I ask because the oil cooler can leak causing this. IDK if it would cause what you describe.
We have been checking in between our tests but haven't seen either one in the other.
 

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had similar problems with New Holland, changed thermostat, checked for exhaust gas in coolant, looked for water in oil.
turned out impeller on water pump would slip [spin on shaft] at higher engine speeds but not at low speed
always a first for everything
 

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You likely have a very minor head gasket leak or a slight chance of a cracked head, but that’s far less likely. The water pump likely isn’t the problem when weird things happen with cold coolant. In this situation, there is insufficient gas venting from the water jacket in the head to the top of the radiator, in fact there likely isn’t any, which ruins a lot of old engines when this happens.
Right now, when any amount of exhaust gets into the water jacket in the head it goes to the highest available space because it is far lighter than the water based coolant. This exhaust gas can’t initially escape to the pressure cap on the radiator because the thermostats are closed tight, so, as the exhaust gas displaces the coolant in the head, the displaced coolant flows backwards through the water pump, but, the thermostats are closed because the engine isn’t up to temperature , so there is actually no place for the coolant to occupy, except to go out the pressure cap and exit the overflow tube.

Take your thermostat housing apart again and drill a 1/4” bypass hole in the uppermost practical area of one of the thermostats.This is a big helping of exhaust gas venting, getting it directly to the radiator cap via the upper rad hose. The tractor won’t run very warm when idling like this in the winter but without eliminating the coolant displacement you are experiencing the engine will ruin itself shortly. In many cases you can get by with a smaller vent, but you need to take a big swing at an engine of this size if you want it to continue a long life.
 

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will be a headgasket. remove the head and have it reconditioned and planed, new gasket and head bolts.costly but it is no good the way it is. might burn a little oil because of better compression but will start way better.
 

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Happened in a 8760, head gasket, coolant in oil. Needed crank bearings done.
 

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Discussion Starter · #10 ·
Thanks guys. I was hoping after lasts nights negative gas test that it wasn't a head issue but sounds like that option is still on the table. The thought of a small leak where the exhaust air is staying in the motor and displacing coolant back does make sense and sounds like a possibility.

Any thoughts on rough cost to recondition the head and replace gasket and bolts? Should I expect that there could be more to fix once we tear into it? We will keep looking for coolant in the oil but hoping the bottom end would still be good (could also send a sample away for analysis). Tractor is also in need of tires so wondering if I am going to start surpassing the value of the tractor.

Thanks
 

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I don't know anything about this engine, does it have an intercooler? We have an old CAT 65D on a pan, was getting similar issues. Like you we couldn't find anything really wrong, it would push water out the over flow when running it but not a lot, never get hot. Intercooler had a very very small pin hole and when making boost it would push some boost pressure into the radiator. I found this AFTER I had the head laying on the bench.
 

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with it needing tires i think you just put another nail in the coffin but a head gasket and bolts will fix your problem. maybe touch up the valves and bolt it back together. you can spend 500$ or 5000$ just depends how important it is to you. my 8440 is near the 12000hr. mark with the head done at 6500 because of poor starting. has had 4 sets of tires in its life time and lots of parts but it owes me nothing and if it died today you just say thank you and move on.
 

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Thanks guys. I was hoping after lasts nights negative gas test that it wasn't a head issue but sounds like that option is still on the table. The thought of a small leak where the exhaust air is staying in the motor and displacing coolant back does make sense and sounds like a possibility.

Any thoughts on rough cost to recondition the head and replace gasket and bolts? Should I expect that there could be more to fix once we tear into it? We will keep looking for coolant in the oil but hoping the bottom end would still be good (could also send a sample away for analysis). Tractor is also in need of tires so wondering if I am going to start surpassing the value of the tractor.

Thanks
Yes, cost for bolts and just the head gasket is going to run around $2000 and JD parts only on those, if I remember correct what my neighbour said.
Headwork extra $$
The neighbour his 8650 has been a problem child.
And don't even think you can just slide a gasket in it.
It might make 100hrs if you are lucky.
 

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Discussion Starter · #15 ·
Hey guys, headed back to the tractor tonight to see if we could learn anymore. Had talked to both the local mechanic and the JD service manager today and both told me that they trust and believe in the sniffer for combustion gas so felt it wasn't a head gasket issue if I did it correct. The JD service manger said he has also seen in the past where the impeller on the water pump will spin freely and sometimes grab which causes stuff like this.

So went back to try the sniffer test this time and did it for 15 minutes with no change in color. However, this time I pinched off the overflow line and forced any air coming from the system to go through the sniffer. After that there was so much air coming through the sniffer I didn't even have to use the vacuum on it. But no color change. After the 15 min put the sniffer near the muffler and changed color within 10 seconds.

Then put cap on and pressure gauge went to 11 psi within a minute (this is where the 10 psi cap cracks). We ran the tractor at 1500 rpm and checked around with a heat gun and watched the system climb to around 78 deg C on the thermostat housing. Once we got this hot (assuming the thermostats opened) the pressure gauge dropped to around 9 psi and therefore nothing coming our of the overflow and cap was closed. The temperature also seemed to stay around that 78 deg C and stopped climbing.

Should also mention that we had the cab heater on high this the entire time but no heat coming out. But when we split the heater lines previously, we had a couple gallons in a short period of time but both sides of the split line seemed to have pressure so I think there is no flow when the lines are connected.

I attached a picture to show the amount of air coming out of the rad with no vacuum pulling it out. Could this be a failed/failing water pump and the gas is localized coolant boiling because there's no circulation? And once the thermostats are opened it moves a bit more coolant within the motor than when they are closed?
 

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We had a 8640 do this as well. Most likely head gasket or head cracked. The 619s were good at cracking heads. With that many hours I would be afraid of finding a low liner protrusion.
 

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Can't hurt to pull the water pump first and check the impeller.
But the thing is sure acting like a bad head gasket.
 

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5 votes for head gasket,one vote for loose pump impeller, gonna be interesting to see what is wrong with this engine. please keep us informed, most excitement i've had all month!
 

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In 28 years of working on jd iron I've seen 1 water pump have a loose impeller and probably 100 heads gasket maybe more. Deere had head gasket issue on all the 619 engines. There was always atleast one inthe shop all the time every spring the 13 years I worked at JD.
 

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You likely have a very minor head gasket leak or a slight chance of a cracked head, but that’s far less likely. The water pump likely isn’t the problem when weird things happen with cold coolant. In this situation, there is insufficient gas venting from the water jacket in the head to the top of the radiator, in fact there likely isn’t any, which ruins a lot of old engines when this happens.
Right now, when any amount of exhaust gets into the water jacket in the head it goes to the highest available space because it is far lighter than the water based coolant. This exhaust gas can’t initially escape to the pressure cap on the radiator because the thermostats are closed tight, so, as the exhaust gas displaces the coolant in the head, the displaced coolant flows backwards through the water pump, but, the thermostats are closed because the engine isn’t up to temperature , so there is actually no place for the coolant to occupy, except to go out the pressure cap and exit the overflow tube.

Take your thermostat housing apart again and drill a 1/4” bypass hole in the uppermost practical area of one of the thermostats.This is a big helping of exhaust gas venting, getting it directly to the radiator cap via the upper rad hose. The tractor won’t run very warm when idling like this in the winter but without eliminating the coolant displacement you are experiencing the engine will ruin itself shortly. In many cases you can get by with a smaller vent, but you need to take a big swing at an engine of this size if you want it to continue a long life.
I agree with the general consensus of compression leaking into the cooling system from a head gasket or cracked block. However I experienced a long running problem with an engine that ran fine until it got under load and up to operating temp where it would lose circulation because the air bleed system had been disconnected resulting in pockets of air not being able to escape to the top of the rad and therefore a steam pocket in the water pump. The PO had also tried drilling the thermostat but there was a bigger problem(s). There was also circulation restrictions in the main coolant flow which all resulted in blowing the coolant out when the engine started to boil in the air pockets from blocked vent lines. I think you did state that your vent lines were operating?? Very important that they are working. Once I got the air pockets venting and the volume of coolant increased everything worked normally.
 
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