Yet another cooling problem

I've done a bunch of searches, but I wanted to get some feedback on likely diagnosis.
Baiscs: 90XJ 4.0 with the closed system. 3.5" lift, 31" AT's. Recently replaced t-stat with OEM, replaced pressure bottle and cap (Renault OEM cap).

Problem: Temp has been creeping up for several weeks on long drives. Mostly on hills the temp seems to creep up way more than it used to, and it seems more variable than it used to be. I drove up I5 from LA to San Fran tonight and in a couple of spots (over the Angeles mtns and the pass from 580 into the Dublin valley - both long grades) the temp crept up to near red. On the ride over the mountain, I had to stop before it went all the way red. Sat for 10-15 minutes, temp cooled down and went on my way. Outside temp was in the 90's. Once I got over the mountain and into the valley, temp went to 100 or so, so I kicked on the A/C. Temp creeped quickly up towards red, so I shut off the A/C. The temp came down, but very slowly, and stuck at around 215 or so, and stayed there for most of the ride. Eventually the outside temp dropped and I was able to use the A/C, but kept a close watch on the temp.

Oh yeah, at one point when I stopped and opened the hood, I noticed that the upper hose was sort of bulging at the top of the t-stat housing. I didn't see any leaks, and the systems seems to be holding pressure. I'm not taking any chance with the hose, so it will be replaced.

Solutions I think I need:
1) Good system flush
2) Fan Clutch & hoses
3) Radiator
4) Water pump

My question is, given that the ability of the system to keep the truck cool is degrading, which of the above is the likely culprit? Is it even possible to tell, or do I just start with the cheap stuff first and work my way up? I'm not sure I'll be able to do the 7 hour flush bit - apartment, no access to hose - so I'm thinking jiffy lube or stealer for a straight fluid flush.

Am I on the right track here?

1) Check the lower radiator hose. If it doesn't have an internal spring, under the higher flow of highway speeds the suction will partially collapse the hose, causing reduced flow and over-heating.

2) If you still have the original radiator, you are overdue to replace. They are only good for about 10 years if well cared for.

Thanks, Eagle, I was hoping you would chime in.

I just did the reverse drive from San Fran to LA, praying that the bulging upper hose wouldn't burst (the dealer in SF didn't have a spare, so I bought one at Kragen, but I don't want to use it, it's crap). More symptoms on the way home that are leading me to believe it's the radiator:

I took it to Jiffy Lube to get the rad flushed and they couldn't do anything. They hooked up a flush machine to it, with the coolant add line to the upper hose and the retrieval line to the t-stat housing - was this correct? They tried to flush the system, but only managed to make the thing overheat quickly. They drained out some fluid, but didn't get a flush at all. Is this because they hooked up the thing wrong or because there is a blockage in the rad (air or sludge or otherwise)???

On the ride, outside temp at 90+, temp ran around 230 (bar before the red) for a large part of the trip. Turned the heat on full blast and the temp settled back 5 degrees or so. Couldn't use the A/C without the temp going up and up and up.

One more thing, when I stopped at a rest stop, I was concerned about air in the system, so I tried the bleed procedure I've used before - run with the pressure cap off until it bubbles, shut it down and wait for it to suck the fluid in. No fluid was sucked in, so I assume no trapped air BUT the engine got hot enough during this that the aux fan came on (217 deg, right?) but the t-stat didn't open. The upper hose was flexible the whole time. I'm assuming that the t-stat is shot b/c of the heat problems I've had over the last few days, no?

Since the overheat is at speed, not at idle, does that mean that the fan clutch is likely fine? What about the water pump? I don't think it's leaking, so I'm assuming its ok......

Hoses and t-stat this week, but I'm wondering if I should just bite the bullet and order the Modine. What do you think?

the story in 4wheel & offroad this month shows a good idea, use a infrared temp gun and check the radiator for hot and cool spots, cool spots show clogged tubes in the radiator, you can tell if the flow is ok or not.

I have a 90 that had cooling problems for a long time. I would suspect two things after following
Eagles advice.. The first is the water pump. When the seal goes bad, it can take a couple of weeks before it goes critical. I assume the place that tried to flush would have seen the leak. there is a hole on lthe bottom of the casting and under the mounting flange that will have water coming out. When it is a slow leak, the fan will spread the water out so it is not obvious.

The second item is indeed the radiator. Mine was 30% blocked after 90K+ miles. Rather than buy a radiator, I had it cored. I am stlll running it without problems.

Re: Yet another cooling problem (Update)

Just an Update

Replaced the Rad with a Modine, replace the hoses and t-stat and she's MUCH cooler now. Ran the same road from LA to San Fran yesterday; had the A/C on over the same mountains and the temp barely rose over 210. On most of the trip she ran 190-200. NICE!!

Now there's some temp creep at idle in traffic, so the fan clutch is next, but for now I'm running cool.

Thanks for the help all.
:cheers:

Thanks for the feedback.