Installed new radiator, water pump and thermostat in my 2002 discover ll. Truck is still overheating. Coolant isn't circulating.(lower radiator hose is cool to touch while all upper hoses are hot. what am I missing?

 

1. Thermostat installed backwards. Belt routing.

2. Do you have a data reading scanner to confirm coolant temp ? If so, what is reading? Lower hose would be expected to be somewhat cooler.

3. If no scanner available, is temp guage above 9:00 position, if so where is it?

4. Overheat at idle or slow traffic - viscous fan clutch (should not freewheel when warm and spun by hand WITH ENGINE OFF) - should turn like 1/2 revolution.

5. Bubbles in coolant? Gurgle / water rushing noises under dash? Combustion gas in coolant from bad head gasket.

6. Coolant loss or white smoke out tail pipe? Head gasket.

7. Coolant in oil? Head gasket.

8. Coolant level?

9. Coolant cap on good?

10. Radiator space between rad and condenser blocked, or fins blocked with mud.

11. If at idle, electric fan polarity reversed?

12. New radiator blocked with shipping material, shop rag, etc.

13. Cracked block behind slipped liner.

14. Low oil pressure (oil pump failing) - you can do manual PSI test

 

How did you bleed the system?

 

And my favorite, fan blades on backward, if they were removed from viscous drive during WP change out - curved side of blade goes toward engine.

When doing thermostat there are four holes on the flange beside that can be pluged with trash as well.

Also, with all this work it is possible that something (RTV blob, trash, radiator stop leekz, etc.) has circulated and cause stat to stick closed or partially closed.

After belt route check, and bleeding air, trash in front of radiator air stream, fan blades right direction (all free fixes) - stat would be a good choice.


Keep in mind that once you are driving at 50 mph, the air flow thru the radiator is doing almost all of the cooling, so fan is minor thing. Water pump is new, radiator is new, most likely is thermostat - or very bad block and head issues. May need to do coolant pressure test, combustion gas in coolant test (chemical from NAPA -$35) [positive for HG leaks]. But check all the cheap stuff first. And don't drive truck if temp guage not staying normal.

If you have a scanner, that may indicate wild temp reading from bad coolant temp sensor and/or wiring. Example - cold engine would not be 235F five seconds after crank up... The coolant temp sensor talks to the ECU, and the ECU "manufactures" a signal to move the gauge pointer, it is not linear, it is not accurate (135 - 235 will look about the same), it is an idiot light with a pointer.

 

Get more specific, when does it over heat, have you checked your viscus clutch, is the electric fan working? As for the circulation, remove, inspect for junk and replace the t/stat, some have been bad right out of the box.

 

Thanks all. Temp gauge readind above 9:00 and in red. Definate gurgling sound under dash. Sad to say sounds like head gasket again.

 

Ouch... How long from cold crank to red line? If "instant" that could be a sensor, as block can't physically go from 60 degrees to 270 degrees in a couple of seconds. Data scanner will show what is going on. Bubbles in system could be from bleeding. And stat could be an issue if stuck. Before you buy HG kit, would do a little more testing, just don't run engine when overheated. Do testing under the shade tree.

 

It overheats at idle and especially when driven. Took it for a test drive last night and she overheated instantly. I havn't checked the viscus clutch. What am I looking for? Had the head gasket done about two years ago. I've been bleeding the system through the inline bleeder in the uppermost radiator hose.

 

OK,
1. If overheating above 9:00 at idle, don't go for a drive. A scanner would really help to tell you exact values, you can see things heading higher than you want before gauge starts to react, this is a "save the engine" issue.

Overheat "instantly" - if you crank truck cold, and at idle, does it also "spike" right away? If you have a bad coolant sensor, or messed up connection to same, might make truck read hot when it is not. Very fast overheat is suspect. Do you have an alternative heat sensor device to use, like and infrared thermometer, or borrow a data reading scanner? Sounds like giant air bubble in system, making it overheat because stat is not getting water around it when it should, maybe elecrical issue with sensor, and the grinch-stole-christmas of HG/block issues.

Attached are pages on the sensor, you can also read with a volt meter.

Now if you are sure engine is overheating quickly, the thermostat could be at issue, along with the base around it. The base has four holes that allow some water to flow even if stat is closed. Stat most likely has a bypass opening as well, that is to allow gas trapped behind it to pass. Stat body needs to be in water to operate correctly, not a steam bath. When stat is closed on warm up, water still flows somewhere, usually that is the circuit in/out of heater. If those four holes are blocked with trash or Oklahoma grade RTV, stat would not operate corretly on warm up.

See attached for more detailed explanation.

Now you might have HG or cracked block - but before jumping off that cliff would check stat and other things, even go so far as to run without stat. There is a chemical test for combustion gas in coolant that you buy from parts store, does lots of tests, so can use on other vehicles. It for sure tells you there is an HG issue. Seems like with this kind of heat you would have coolant loss, white smoke out the back, steam in overflow bottle, or something.

 

I am getting gargle in overflow bottle and lot of steam out of bleeder. Only smoke out of tailpipe was after first start. Truck sat for a week or so and temps around here are dropping pretty quickly at night. Smoked for a few mins. No visable coolant loss though. My gut says that thermostat isn't functioning properly or system isn't bleeding. How else can I bleed system.