I went down a rabbit hole here recently that ended with having to redo the trans cooler lines again. The biggest problem was fan blade clearance, since the fatty wagon came equipped with electric or hydraulic fans, as opposed to the belt-drive fan that's fixed to the shaft of my water pump. Whoops.
A bigger whoops was closely avoided when I started to take the alleged need to route through the integrated cooler in the radiator at face value. I almost ended up plumbing things to run through it until I actually sat down and thought it through. Here's the deal:
A lot of sources say that running the trans fluid through the integrated cooler is a necessary step to ensure the trans fluid is warmed by the coolant in the radiator. Bypassing this cooler will have the effect of shortened life for the bands in the transmission, as a consequence of stress put on the steel through excess expansion and contraction. Let's think this through a little bit. . .
As your engine is warming up and working to reach op-temp, your cooling system is closed. This is so you aren't constantly pulling heat away from the engine and delaying it from reaching the temperature range where it performs most efficiently. This is why it's necessary to replace a thermostat that becomes stuck in the open position, as you'll be inviting a slew of problems if the engine runs cold for excessive periods of time (loss of power, guzzling fuel, overly-rich exhaust that can foul cats, and so on).
Once the coolant in the engine passages reach the temperature needed to allow the thermostat to open fully, coolant will pass through the thermostat opening and cycle through the cooling circuit (i.e., the radiator), allowing the engine to run while keeping it from overheating. Generally speaking, an AMC 258 thermostat will be rated to be fully-open at 185°F, which means it will actually reach that point around 170-175°F. Keep this in mind, as we'll be coming back to it.
While the thermostat doesn't go from fully-closed to fully-open like an electrical toggle switch, the duration of travel doesn't appear to take so long that the cooling circuit will be providing coolant of sufficient temp to warm the transmission oil during the earliest point of the engine's warmup period. Really, until the thermostat is fully open and all coolant has cycled through to reach roughly the same temperature, the coolant in the radiator has the lowest temperature out of the entire cooling circuit.
Then there's the warmup procedure itself.
The way of warming up an engine that is least efficient and causes highest wear to an engine is to let it idle until op-temp is reached. Best practice is to start the vehicle, let it idle for a couple minutes, then put the engine under light load until it's fully warmed. During these first couple of minutes, the thermostat will be closed (or close enough to it to where any warm coolant that would be introduced to the radiator will have negligible effects on the radiator coolant temperature), which will be sucking away any heat in the trans fluid. Since this will continue to be the case until the radiator coolant warms sufficiently, at what point does the overlap of the transmission oil being at a lower temp than the coolant occur? If you have an answer for this, please post a comment to enlighten me, because I'm at a loss.
Up to this point, there's been a key detail that's gone without attention: the proper operating temperature of the transmission fluid itself. This is where things get really confusing to me, as I'm of the understanding that the proper temperature for the oil in these torqueflites should be around 180°F, which is warmer than the temperature at which the thermostat can be expected to be fully open. Now, an unmodified torqueflite will not be pumping fluid while in Park, so it's conceivable that you could be delivering warmed fluid to the system if you remained in Park until the point where the thermostat is fully-opened, the coolant temperature has reached equilibrium throughout the circuit, and it has transferred the heat to the transmission fluid in the integrated cooler, then put the transmission into gear. Leaving the details of inconvenience and bad practices aside, isn't this kind of extreme heat fluctuation exactly what the cooler/"warmer" is supposed to be preventing in the first place? If you've installed a shift kit that allows the fluid pump to be engaged while still in Park, the thermal shock in this scenario could be mitigated, though the fluid is still going to suffer from it's heat being wicked away by the coolant.
Following this reasoning, the ideal configuration seems to be one where the fluid is pumped while in Park, which will serve in getting it warm as it flows through an external cooler that has minimal airflow over it during those first couple minutes of warmup. The best way to accomplish that would be either by having a thermostat-triggered fan mounted to the cooler, or a water pump fan with a clutch. I have neither, so I'll be making due with being mindful in my cooler placement.
If you're still awake, you might be wondering why the hell any of this even matters in the first place. Honestly, for most people it really doesn't. In my case, I need to be reasonably sure that I'm not going to be causing damage to my transmission that will cause me trouble as I'm on the road, and I needed to weigh confidence levels. See, I've already had one transmission die from the radiator cooler allowing coolant into the trans fluid circuit, so I'm already very distrustful of the design.
In doing research on the issue, I found that it transcends manufacturers, models, years, OE or aftermarket parts, and so on. Coolant will, at some point, cause that barrier to corrode through. That's a dead-in-the-water show stopper, right there. Now, if you believe what some people say when they assert that the integral cooler is necessary, you'd suspect that bypassing the cooler in favor of an external unit will lead to equally calamitous results. This may be true if you're towing tons of material through mountain passes or whatever, but in my case it doesn't seem that it's something to worry about.
A cheap radiator causing the inside of my transmission to be filled with strawberries and cream? That's something I'll be making damn sure I eliminate as a potential reality.
No comments:
Post a Comment