Have you verified your belt routing yet? If it is correct and your radiator is good(not plugged), then your best bet is to order a water pump and replace it. Can't hurt. But as said before, check your radiator!!!! It may need rodded out at a shop.

 

The impeller in those water pump is "staked" on and is known to come loose and no longer move the correct volume or flow of water.

Keep overheating that sweet liitle engine and the humm will undergo a drastic tonal change and get nasty in a big hurry.

 

OK... Thanks for all the suggestions. I REALLY MEAN THAT!

First off... serp belt is fine and routed correct. Tested for exhaust gas in the collant via test kit from AutoZone. Liquid stayed BLUE. Neg results (see picture). Not convinced the test is 100%... but that may be me. It did turn yellow from my breath when I tested the kit. The guy at AZ suggested I order a new temp sensor. Don't agree with that one. The aux fans come on by themselves when the engine gets hot as they are supposed to via readings from the temp sensor. Culpret is the air not delayed fans. For all the years we have had the truck the fans NEVER came on by themsleves except whern the AC is switched on.

The heat guage has always been at 9am... every season for 7 years or so.

Think water pump is OK becasue i can clearly see collant moving in the RAD . The truck on cooler days does not overheat for a while... but it still does eventually if I drive it hard. In thevideo you can see collant move along with lots of air between flows. Truck is ingesting a ton of air from somewhere.

Radiator was boiled out and tested 2 or 3 years ago along with a new WP from AB. Noticed the remaints of a small leak along one of the rad walls (see picture). May be an old leak as nothing is ever wet there. Checked in the early am if a leak I would expect to see wet collant after sitting overnight. And with the pressure building up I would expect any rad leak to really leak! NADA. BTW... prerssure is less than 15lbs... which is what the rover exp caps are set for on the 3.9.

Maybe the rad is clogged down below and I am not getting enough flow on hot days? But if clogged below how is the collant gettign to/from the motor? Has to be the source of the air that is the gremlin. The upper hose contains collant and if squeezed I can see the level in the expa tank go up and down. I had expected the upper hose to be more firm. It is soft? The T-stat is out... maybe un obstructed collant flow (no Tstat) would keep the hose pressue down?

If I pull the lower and upper hoses and flush the rad with water... I should get a solid strong flow out the bottom with a garden hose feediong the top yes? Fairly inexpensive test.

See pictures below on all this. Also made a video where you can see the air burping into the exp tank.... see the coolant moving in the RAD... HEAR the air after the truck is turned off... sounds like boiling inside the motor. Hope the link works for all.

I am starting to think that the HG has a problem despite the neg test results for exhaust gases in the rad? Did order the "In Search Of" in case I have to tackel that.

Continued comments appreciated.

Movie is here BTW. Combination of 3 clips. Truck sounds MUCH better that the video sounds... senative mic I guess:

‪UltraHotRover.flv‬‏ - YouTube

 

The tubes run side to side, so it is possible to have a partially blocked rad, and still flow at top; just just won't cool offlike it should. Might show up as hot/cool areas. Were it under my shade tree I would pull rad and take to shop. Too much risk of it getting worse on engine.

 

Have you tried just rinsing the radiator fins with the garden hose?
When I drove truck I had one that after about 500,000 miles it started to overheat for no reason, turned out the fins of the radiator were full of dust, pollen and bugs.
Mechanic "washed" the radiator with the hose, both sides and all was well once again.
He had even removed the thermostat first thinking it was stuck, but it still overheated on long grades on hot days.

 

10-4 on the hase job. Coil cleaning is an annual event for my roof top AC units at the office, they get dirty just sitting there sucking in air to cool off the compressors. On a Rover, there is also that space between radiators that is sealed up with rubber strips, to keep lily pads from getting in there during wading. Great place for leaves and gunk. Should be able to dangle a shop light or a flashlight behind the radiator and look through to evaluate dirt level. Lower fins can easily become caked with mud. Don't use a pressure washer - too easy to damage fins.

But from what you have said it points toward radiator blockage of some type - air flow is correct direction, system operates OK on cooler days, so it is "marginal". Thermostat would show up on cool days as well if stuck closed. Water pump would be second choice. It is possible for them to loose blades off the impeller, corrode down to nubs, or slip on the shaft. Radiator could easily have blockage in lower section, reducing cooling capacity, but not gallons per minute of water pump. My indy rad shop says a healthy radiator should be within 10 degrees or so top to bottom (on the fins, not the tanks). If someone in the past used any of the ever popular head gasket fixes / leak stops, they can restrict things.

 

Do you have an air compressor? Blow it out good from rear of rad to the front of grille and see if you get a dust cloud. Then reverse and blow from the front to the engine. See if that helps any.

 

Thanks to all for your input. The rad fins are clean. There is no mud, no dirt, no obstructions. Wish there was a way to really test the radiator. Will try to flush it and try to match pressure in for pressure out. if way off then yea the radiator has a blockage.

Even with a clogged radiator... does not explain all the air. Almost wish the test for exhaust gas came back pos. It did not. Would hate to pull apart the motor, spend 40 hours over a couple of weekends (joe's speed) only to get deep inside and find nothing.

New water pump is an easy part swap test... and cheap too may go that route first. Worst case scenario I'll have a spare water pump.

Have my nephew's friend who is a senior Toyota dealership mechanic... All the Toyota certs possible. Has worked on many Rovers and Land Cruisers in the past... will see what he thinks.

Joe

PS... one thing we noticed last night. The motor hums along and sounds sweet until she starts to overheat. At about that time we hear a little knocking sound... tap, tap, tap, tap. Like a rocker arm needs to be tightend down ( I know this is hydro, just saying.) Quick test drive HOT.... hard aceleration for just a few seconds.... thought we would see some white smoke... nothintg... but the motor knocked quite a bit almost like bad gas or sudden misfires on one cylynder.


Joe

 

If bottom several rows of tubes are 100% blocked, pressure test will be inconclusive, as water in = water out. With unit warmed up, turn off, then measure temp on different areas of the fins, top to bottom. Much cooler area = little water going through there. Water pump is easy to change, once you remove fan clutch, which is all in the wrist, just a quick pop to the left.

Pix of what you may see with water pump, left side is a leaky one that was wobbling the pulley. El cardboard bolt arranger - several different lengths. Brown coating is good old leak stop - it coats every surface inside the cooling system, and the rest of the bottle goes to the low spot - the bottom rows of fins in the radiator. Just like stirring up mud in a glass, most of it will eventaully settle out.

"Water wetter" from the parts store will reduce the temp quite a few degrees, it may be steam bubbles you are seeing from poor cooling. And of course, you need to get rid of all the air in the system.

10-4 on water pump is simple and cheap, but you may have multiple marginal things that add up to trouble.

Knocking could be low oil pressure. Suggest you do a mechanical oil pressure test, you will have to remove oil PSI switch that is near the oil filter. Oil routes thru radiator on battery side (oil cooler). I pulled a rad from a dead Rover, 95% blocked oil lines - what killed the old girl.

 

The tapping you hear as it is overheating is the oil thinning out to much and not protecting the valve train.