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I have a 2003 Kia Sedona with about 140k miles. 8 months ago I replaced the thermostat without noticing any issues with temperature gauge because the check engine code kept coming on. 3 months ago I had a mechanic replace the AC compressor and receiver drier because AC wasn't working and that fixed the problem. 2 days ago my wife said the temperature gauge was all the way to high before she noticed it, but no steam and no check engine code. AC wasn't working either. Turning heat on full blast didn't drop the needle.

I waited until the morning to check it out. I couldn't get it to overheat after 20 minutes at idle, stayed at normal temp on gauge. A couple miles in the neighborhood at 25 mph and it still ran at normal temperature. The second I left the neighborhood and sped up to 45 mph the temperature gauge needle started moving up quickly. Coolant reservoir is full. Heat works well in front, AC works (maybe not as cold as normal?). No heat (cool air coming out) in rear of vehicle. After reaching normal operating temperature the fan comes on. Radiator cap and radiator are both cool all the way down. Heater puts out HOT air, but doesn't move temperature gauge needle.

I'm thinking the water pump is bad, but does that line up with my heat working in front but not the back of vehicle, radiator being cool, turning heat on not dropping temperature gauge at all, and not overheating at idle? I thought that the pump had to run to get hot coolant to cross the temperature sensor to have the temperature gauge register a problem? Any thoughts? Thanks for the help!
 

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Check the coolant level in your radiator. My 2003 was overheating while parked and the reservoir was full. I checked the coolant level in the radiator and it was low.
 

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Discussion Starter #3
I replaced the thermostat and that solved the overheating. AC and heat in the rear of the van are a separate issue. Still don't know why I didn't get an engine code if it was the thermostat, but I'll gladly take a cheap fix. Thanks.
 

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I replaced the thermostat and that solved the overheating. AC and heat in the rear of the van are a separate issue. Still don't know why I didn't get an engine code if it was the thermostat, but I'll gladly take a cheap fix. Thanks.
  • Heat in the rear is NOT a separate issue.
  • First, check radiator when cool to see if the coolant is up to the neck. If not you need to fill the radiator up to the neck and run the engine to operating temp. Then, check the radiator again when cool to see if the fluid went down or is still at the neck level. (now, my recommendation is to get those radiator filler kit on Amazon. It's a bit pricey but I don't know how many times I used it and it paid for itself - it has a bunch of radiator neck adapter and a funnel that snap on so that it stays up and you fill it with coolant and as the enging runs you get the bubbles out of the engine and radiator - it's around $50 I think)
  • Sedona engine (Mitsubish) takes long to heat up so you have to run it like 30 minutes.
  • As you fill the coolant and running the engine, you SHOULD get heat in the rear (have the heaters on full blast with the rear heater on).
  • If you don't get heat heat in rear, you may have pluged heater core or leaking pipe.
  • Cycle the fill and check the level. _ DO NOT TRUST THE RESERVOIR LEVEL. - open the radiator cap when cool to check.
  • If the fluid level is okay, then you are not leaking somewhere. If it's down, fill it again and do the cycle again.
  • If the fluid level is down again, then you are leaking somewhere.
  • If you are up in north, you may have a small leak along the two coolant pipes that run to the rear heater core. The metal pipes are notorious for rusting and leaking along the line. Mine did.
  • Check carefully, because if you have a leak there you will not have rear heat and also you will loose coolant in the engine - then high temp and death to engine. ( I had two issues when coolant lose occurred, leak along the heater pipe underneath and leak in the radiator)
  • If you have a leak along the heater pipes, replace them with coolant hose (cheapest solution). Kia realized that pipes rust so the parts got cheap but it will rust again.
  • Get a long hose (you need length for two pipes) with diameter that's slightly smaller than the outer diameter of the pipe so that when you put it on the pipe, it's tight ( if i remember right i got a 1/2 inch inner diameter hose but check for yourself). The pipes are actually separated by short hoses underneath. So, I did not cut any pipes at all. I just removed those at nearest to front and back side and put the hoses on both pipes with hose clamps (input and return line) [ didn't cut so that the ends still had flares and hoses got on really tight there]- Make sure you do not mix up input and return lines. I zip tied the hose along the pipe (not worth taking the pipe off for too much hassle.
  • If you have any air in the system, you are not having the coolant circulating right even with the water pump running, air makes the cavitation and that's not good.
  • Also, check the radiator if it's leaking. When it gets old, it can leak along the seams. Mine did (around 170,000 miles). I borrowed coolant pressure tester and put pressure in the radiator (you have to pinch the hose that goes to reservoir with something - careful with the hose, don't tear it - I just changed out the hose with a generic hose - cheap to get at parts store). And I found a leak along the right side vertical area. Bought new Duralast radiator from AutoZone.
  • Make sure to check the two big radiator hoses (should really replace them at the mileage). They are cheap.
  • Make sure to check seems along the thermostat housing, it's vertical so it may leak around there if not tight.
  • If the coolant pipe or radiator is not issue then you may have head gasket issue.
  • AC is a separate issue.
 
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