Here's the background:

Just did HGs back at the first pf the year. Decided last Saturday was a good time to flush entire coolant system and change out the Dexcool to G-05 and replace all the hoses, 180 thermo, etc.

Finshed up, burped the lines and test drove it. Ran fine. Drove it for the next three days to work; about 12 miles each way...1/2 freeway, 1/2 surface streets. Temp. never went past 1/2 way, ran fine. Everything great until Wednesday morning when one of our (Calif.) newly licensed illegals was texting, made a lane change and bashed in my right rear 1/4 panel. Another story.

So I had to go to a meeting after work; about 30 miles past my house. Ran fine until I got off the freeway, temp immediately began to rise. Pulled over. Noticed aux. fan was not on. Let cool. Restarted and brought engine to about 2k RPM and temp came up to normal and stayed there. Turned on A/C and aux. fan came on (not relay or fan). Shut down until after meeting.

Started up and headed home. Temp ran at 1/2 way...slightly above, while on freeway. 1/2 way home, pulled over to check and temp immediately started to rise...no aux. fan without A/C. Let cool and got back on freeway, turned heater on high and went directly home.

Now to the question. Should aux. fan be coming on other than when A/C is engaged? I know there are two temp. sensors (mine has SAI); one on the front of the lower intake manifold and one on the radiator, right above the lower hose connection.

I've also heard stories of a cylinder liner slipping to the point of allowing combustion gases to enter the coolant passages and/or liner cracks doing the same thing. Anyone have experience with this happening? I'm assuming this would create a measurable increase in pressure in the cooling system, no?

 

The AUX fan comes on at specific times indicated in the RAVE. I would also invest in an ultragauge or similar ODBII scanner that can display coolant temp. The factory gauge is not accurate, buy the time it even moves slightly from 1/2 you are already way over heated. With a 180 tstat and a properly working coolant system you should be around 188-190 on the highway and around 210 during the hot summer with A/C on at idle. Exhaust gases can enter the coolant but will usually show with rock hard coolant hoses and blowing coolant out of the overflow tank. Did you check your coolant level? Was it low? You can test for exhaust gases by renting a tester at Advance Auto, Autozone, etc..

 

Oh one other thing to check, does your aux fan spin freely? If its frozen up like mine was it will blow a fuse. I got a used one from Paul Grant and replaced the blown fuses mine comes on as it should.

 

Aux fan works FINE when A/C is turned on. Are you talking about the radiator pressure tester at AutoZone? Because it doesn't come with the adapter for European cars.

 

The fan should come on at around 212 regardless, u should really buy a scanner with live data capability so u can read the actual temp the engine is running at, the factory gauge is really just an idiot light in disguise, not helpful at all

 

Ok already!

I HAVE a live scanner; I know overheating when I see it!

I think I may have had a faulty 180 Tstat (only a few months old), a defective aux. fan switch and/or a defective fan clutch. What's the chance of these going all at once though?

 

all going all once; slim, failing one by one and you not knowing; good.
is the t-stat white or dark gray?
if you have a scanner check and see it your aux. is coming on at 210.

 

Its got the 180 tstat (dark gray), I just installed it a few months ago. The aux fan seems to be coming on at about 210, but sporatically; ordered new temp switches and I think I'll be needing a new radiator. Fan clutch tested OK and the block test for combustion gas in the coolant came back negative. Twice. Always double check...just like a prego test!

What's the opinion of the Nissens units? Who makes the OE radiators?

 

yep. Fan comes on at 212 degrees.
Mine did.
I cured it by:

Replacing Radiator with a good Nissen Radiator from Rockauto.com
Replace fan Clutch.
Put in 180 degree soft spring Land Rover Thermostat - the gray one.

Make sure all the dirt is out of the oil cooler trans cooler and A/C condenser fins.
That's about it.

 

I don't believe your truck should be getting that hot. Mine with the gray t-stat and good everything won't go over 205° even climbing mountains in 90° summer heat at 10k ft in elevation. Might want to replace the fan clutch if you haven't yet. You can switch to a late DI two piece fan and buy a Hayden HD fan clutch for about $70 over the single piece $300 DII job

Sorry one of the "licensed" illegals mashed your truck. Similar thing happened to me back in AZ and totaled my pride and joy restored muscle car !