Nice idea but I see a problem with that explanation. The engine promptly heated up when the return heater was completely pinched off and cooled again when hose was unclamped at idle. If the thermostat was allowing coolant the flow past it, then I would not expect the engine to heat up at all, irregardless of the return heater hose clamped or not. I will still ask them about your possibility. Keep considering the various possibilites.CATMAN said:Well, I'm going to thrown another idea at this. I been looking at the water pump and thermostat area on JD parts again. I noticed something unusual for the thermostat area and its gaskets. It shows a gasket( #4 on graphic) and it looks to be typical gasket paper. Then it also shows another gasket below the thermostat(#6 on graphic) My guess is that it is rubber and probably has a slit on its inside diameter and it actually fits over the the perimeter of the thermostat. What is unusual is that I normally wouldn't see this combination together. Typically, It is thermostat/ paper gasket OR thermostat/rubber o-ring-like perimeter "gasket" that acts as the seal for the top radiator mounting flange. I haven't seen both used together before. Now, what if they MUST be used together to create a tight seal so no coolant excapes to the radiator thru the upper radiator hose. Is it possible that the #6 rubber gasket is missing from the perimeter of the thermostat, thus coolant could flow around the thermostat(even thou it is completely shut internally) and allow coolant into that big oversized radiator just enough to not allow engine to warm up. If any mechanic was not used to seeing this type of design before, it could easily be overlooked during the thermostat removal, testing ,and reinstallation process. {the thermostat would be sloppy in its bore thou} You had mention once that you measured 77F at the radiator top tank on a 50F day with 125F at the engine block. Did the 77F get there from just the transfer of heat with stagnet water, or was it thru some warm water "flow" that allowed that temperature to rise to 77F? It wouldn't hurt to ask the mechanic if he remembers the #6 gasket(rubber, I assume) under or around the thermostat he tested for you?
Lower plug 24 connects to a line which goes to the base at the attachment of the spin on oil filter. I assume that is an oil line. (It is listed as 12 under oil filter category). Upper 24 plug seems to be the feed hose connection for the heater, although the diagram lists it as a pipe.CATMAN said:Hi radman, I looked at #32 plug and see it uses a copper washer on it (#31). A copper washer suggests to me that it is a plug used for flushing out the system. The graphic isn't detailed enough for me to tell you exactly where it goes positively. I would need to be able to rotate that graphic. My best guess is that it is water/coolant coming out of the cylinder head, thus used for flushing the engine and the idea of the copper washer is that they are reuseable(sometimes). If correct, then it is on the "pressure side" of the system. I wish I could see the casting of the water pump itself because it should have a by-pass passage between T-stat housing and water pump impeller. If plug #32 is in the by-pass passage, then there would be maybe some suction, but yet some pressure from the cylinder head flow. I can tell you this is a fine line at this area with the water pump so close. I do have this experience to share with you, back in 1988-1989 CAT had an engine that the OEM manufacturer (Freightliner) plumbed their heater return directly above the by-pass tube(about 6-7" away from the water pump) and the complaint was poor heat in the cab. The solution(Update) was to reroute that heater return to that special suction fitting on the water pump itself. To me; that special fitting on the JD water pump would be that lower #24 plug. See how it goes directly into the water pump suction. [one can tell because we know that bottom radiator hose fitting/smooth barbed has to be suction. I think your oil cooler coolant return goes to that "special" fitting (lower#24) Again, I assume that because of the oil cooler graphic and its hoses[ it gets pressure for the rear of the block, goes thru the oil cooler, then forward up to the water pump at lower #24 plug(suction)] I am curious about pipe #28 and pipe #30. JasonMac says his 3720 heater works fine in New Hampshire, So I keep wondering where is your heat escaping to and/or why the engine doesn't generate enough heat in the cooling system. Even the oil cooler actually takes heat away from the water until it gets up to temperature and then when a engine gets worked really hard, then the oil is generally 20-40F hotter than the engine coolant temps(CAT systems,anyway)
radman1 said:tglass
Since your engine is different than a 3520 or 3720, does the heater hose return line "T" into the radiator hose on your tractor?
radman1 said:turbo36
Did you have the heat problem on your tractor checked?
