Van Overheating No Clear Diagnosis

My brain is not big enough to process all that information. I think the problem started off low on coolant. Top up the radiator as well as the overflow bottle. Also, coolant sensor may be falsely indicating it's overheating when it's not.

see if the fans come on when it gets hot , make sure the coolant is full , you already have a new thermostat , is the exhaust white ? Is there goop under the oil fill cap ? Those are signs of a blown head gasket and a compression test should be done , you can pull one of the smaller heater hoses to see if the water pump is circulating , then a flow test on the radiator to see if it is clogged , Or keep throwing money at mechanics that do guess work instead diagnostics

U have 2 radiators of sort. Large one in front of engine and small one (heater core) in dash for heat. They are usually seperable. U can run a car without the one in dash, its only for or heat. So no heat in winter could be bad heater core or a few other things usually in dash or by firewall, etc. The car itself overheating I would think is a separate issue. Because u don't have consistent overheating night vs day/slow vs highway seems to suggest a clogged system that may have clogged heater core too. Did u mix antifreezes, if u do sometimes it can gel. Is there air in system? Ur loosing fluid, since u needed to add, is there a leak. Park in dry spot and check to c later for antifreeze. Electrolisis has to be checked with gauge (Google it). Could be a bad radiatort too. Have someone point a laser temp reader (u can buy for $15.) at radiator what's temp at top than bottom? Should b hot at top, cooler at bottom. Check too wen car starts to get hot do fans kick on. They have to to cool water. DONT overheat car or u could blow head gasket, etc. U jus have to patient and figure by process of elimination but jus remember its not rocket science (but sometimes close to...lol) Let us know what u find OK...hope some of this helps

That's an interesting thing to say. Am I doing something wrong with these mechanics or is my experience normal? Thank you all for your responses. The mechanic said the coolants were mixed so I am assuming it could have happened during an oil change because we just coincidentally happened not to go to the same place twice and they always "top" it off. Should we flush the system then? By draining, putting distilled water through, then filling it to the top? Like a fool, I was going to take it to an actual shop, thinking they would do something more extensive. But I am going to check all of these things and get back. Just wanted to thank you guys.

Does this make sense, the mechanic and I are going back and forth about the waterpump. I asked him why the car is not getting hot with just adding water and he didn't explain. So he said the electrolysis has occurred due to a tiny amount of metal in the coolant and then I asked if he thought the water pump is the damaged part and he said this: 1/3 It is a damaged part no doubt about it . If it was working properly the temp would have dropped when the hi fam came on and the t stat opened . It only had a momentary dip then it never decreased in temp the way a full flowing cooling system does. The impeller is damaged . I don't have to see it I know it 3/3 is.

Concerning water pumps: it's not uncommon to see a water pump made with plastic impellors, and they are known to deteriorate over time. This will lead to overheating if the pump won't pump.

My suggestion...research how they test for eletrolysis (knowledge is power) than ask urself did he do the proper testing to determine that. Usually when they top off coolants they don't wanna b sued so I would assume its not that. Ur cars fairly new and toys r well built I wouldn't think radiators bad (laser thermometer can tell u if its cooling by time it hits bottom). So l would lean toward water pump. How bout another mechanic giving u another opinion? And also again do fans kick on. When water pumps go bad they usually start leaking by shafts, etc any antifreeze by it?

He did not check for electrolysis and also said there were no visible leaks but watching videos it seems like the best way to tell would be to have the car lifted up and he did not look that way. But he did look underneath the car in the daylight.

Put a large piece of cardboard under engine and run it but dont overheat it. Let it set overnight than look at it in morn. Notice exactly where spots are if they are there. Seems ur loosing antifreeze somewhere! Its typically a sealed system, they don't just typically leak.

JUST DISPLAY COMPUTER FLOW CHART FOR ALL CHECK POINTS: CAR HAS COOLANT-Y/N>WITH DISTILLED WATER-Y/N-HEATING MIDDLE THAN COOL LEVEL-Y/N-CONDENSER+RADIATOR-CAR DRIVER SEAT LEFT DASH BOARD SENSOR AND RADIATOR FAN CONNECTED-Y/N-RADIATOR NEW OR 2 YEARS OLD,COPPER OR ALUMINIUM? THERMOSTAT NEW-Y/N,PUMP 5Y OLD-Y/N,ANY LEAK IN COOLANT RESERVOIR, CAR RUNNING GOOD-Y/N, WHEN CAR IS GETTING HOT COOLING FAN TURNS ON BY IT SELF, REPLAY FAN 1-2- 3 AND AUTOMATIC MAGNETIC CLUTCH CLICK NOISE TELLS SYSTEM IS NORMAL. CAR JUMPED FOR A/C AND A/C WORKED FOR SOME DAYS AND NOT OVER HEATING AGAIN NO LEAK. CASE HISTORY:AUTOMATIC-2002-TOYOTA SIENNA-SYMPHONY-3.0 ENGINE 1MZ FE-IRIDIUM SPARK PLUGS, WALMART BATTERY,300K MILES, 2 TRIP SAN JOSE,CALIFORNIA -SAN DIEGO, TRANSMISSION EXCELLENT. MECHANIC DID SOME THING SECRET ONE FRONT RADIATOR CONDENSER SENSOR,WATER PUMP OR BAD RELAY CAR MANUFACTURER QC AND BOGUS PRODUCT APPROVAL IN USA AND ISO STANDARDS WHERE NOT TESTED IN FRONT OF TV CAMERA

LET COOLANT DRY OUT IF BUBBLES FALLED FROM RESERVOIR BECAUSE HOT STEAMED LIQUID FALLS IN SOCKETS