If the van is overheating and the coolant is low, you need to add coolant. If it's still low, you have a leak. I'd probably take it to a trusted mechanic and say that you believe you have a coolant leak and then let them fix it. It can leak from a hose or the water pump or the neck or the radiator or a bunch of other places. Worse, when you have one small leak, you often have several other small leaks. Worse still, a small leak can rapidly turn into a giant leak and strand you or destroy your car.
Engine Overheating at low speeds - Coolant System troubleshooting
2004 Sienna LE FWD with 140k miles on it (original owner). My college bound son has been driving it most of the time recently
We are relatively newbies as far as intricate knowledge about all components of cars and looking for some advise and guidance.
Here is a chronology of events:
![Tire Wheel Car Vehicle Automotive tire]()
We are relatively newbies as far as intricate knowledge about all components of cars and looking for some advise and guidance.
Here is a chronology of events:
- Last week noticed that during a traffic jam that AC stopped sending cool air but seemed to be working better at the higher speeds on the highway
- Couple of days later when he drove it again, noticed that the engine was overheating at lower speeds (going above 50% in the H to C temp. gauge on the dash and going to normal temperature below 50% on the gauge at higher speeds)
- Drove aound 70-90 miles over couple of days in this situation
- Finally when we started troubleshooting, noticed coolant reservoir was very low, so added 50-50 mix of anti-freeze. Tested the radiator fans and they seem to be working ok, with even the speed increasing (just observed listening with hood open, without tools) when engine started to warm up
- Test drove again next day (Friday) and only noticed a minor blip of overheating even at low speeds
- During the weekend with most mechanics booked up or closed on Sunday, spent time with my son learning (on youtube) all the components of the cooling system (radiator core, fans, thermostant, coolant thermostat sensor, hoses, head gasket, water pump, heater core etc and how everything works together to keep engine cool as well as the cabin airconditioning which has its own incremental parts like condensor, freon, etc)
- We also noticed potential leak marks underneath including dripping today from the front near radiator area. But with overnight rains we were not sure where exactly the leak might be. More on this later.
- Took it to a mechanic today and he only had enough time to do a 30 min evaluation. He added water in both the opening with the pressure cap (added probably around a quart or two) with signs of some air bubbles and also in the reservoir tank. Then wanted to do a pressure test through the raidator cap opening but Toyota messed up design/placement of this opening because there is not enough vertical clearance/space to add a tool on top (mechanic even tried jacking up engine at angle to create space but to no avail).
- Mechanic narrowed down to radiator potentially being the issue and is going to quote on that but after getting back home we think there could be another issue
- Side note: While mechanic was working on this he noticed and we too for the first time that at low rpm with AC turned on, the condensor/alternator area where thebelts are running was making a clicking sound. He suspected it to be Freon imbalance and proceeded to address that by adding Freon with pressure gauges hooked on and artifically increasing RPM temporarily using some tool he got and adjusting something underneath steering wheel area)
- When we got home, my son and I proceeded to inspect the leak. We did not see dripping from radiator area like we had seen earlier (so probably that was rain water). Instead we noticed that there was some dripping/leaking potentially of the coolant under the car (in area right below where the passenger side- pic attached) . Put few layers of paper towels and it was clear. Most likely its the distilled water (that the mechanic put in) because that general spot seems to be where the previous coolant drips had dried up in our driveway. Only other thought is that it could be condensation from AC working (unlikely, but just putting it out there based on a theory floated by a person I spoke via phone at dealership).
- So the question is if the coolant is leaking from that spot does that help narrow down which part of the system. Only one I can think of that far back could be the water pump (which can be labor intensive to replace, hope its something less simpler and cheaper to fix)
- FWIW, we test drove at different speeds for about 3-5 miles with AC at full blast and did NOT notice the engine temperature exceeding beyond normal and also AC working better (probably due to added Freon)
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