I have a problem to help challenge your mechanical minds!

I'm a firefighter living in the mountains just west of Denver. I have a 1998 V70 awd with the turbo at 130,000 miles. I do have a larger turbo and injectors plus a tune from ARD; all new, quality parts. I have an issue with overheating that I can not figure out. It will idle all day just fine somewhere around 200-220, the fan kicks on at 217 and off around 205. I tested both fan speeds to be working via grounding the relay, although I can't say I've ever witnessed the fan going in to high speed.
The problem is that on any long, sustained climb or sustained acceleration, even moderate to low, the temp will just creep up. And by up i mean 230, 240, I've even seen 250s, at which point my cap starts to spit out my coolant as expected. I assume that's too hot for it to run?

I replaced the thermostat, I've flushed the system with water, also the coolant flush addative where I drove about 20 miles, I replaced the ECT sensor, generic. If I put a hose in the upper radiator, water will come out as fast as I can put it in out the bottom hose, so there are no restrictions there. I have hosed out the fins of the radiator (which is of course behind the intercooler) and neither look dirty. I can see a flashlight shined through it.

I have pressure tested it to 20 pounds which it holds well for at least an hour. The pressures don't increase on startup so there doesn't appear to be a pressure leak from the head gasket in to the cooling system. The plugs are dry after pressue testing, there is no smoking on startup. I'm running 50/50 of old school green antifreeze and distilled water.

I gave up and took it to a shop, he said there were no combustion gas leaks so the head gasket is intact. He theorized about the water pump not working, which I didn't think would be an issue. They wanted $1200, so I did it myself. I could not see any issue with the old pump or belt as I guessed.

Now it runs great, and it maybe cools a little better, but on a sustained climb up a mountain road over 10+ minutes the temps still crept in to the mid 230s before I gave up and turned around to head back downhill, where it cooled to 195 within about 2 minutes.

So I'm at a loss. I know the only thing left to try is the radiator, but that looks to be a good bit of work with the trans lines in there, and frankly unlikely at this point since it flushes and light shines through it. Otherwise wondering if somehow the expensive blue volvo coolant would magically make the difference over my classic green (which I know is best for aluminum based on my land rover days).
Is there something else I'm not thinking of?

 

One thought is you can rent a quality OBD2 reader and monitor the engine coolant temperature in real time. Before ripping out the radiator, you may want to try another thermostat (I've had a replacement fail on me...).

I'm also wondering if the engine tune and timing is spot on or if there's a slight lean condition (vacuum/air leaks) causing the engine to produce more heat (advanced timing/lean burn = more heat)

You can try a more aggressive flush or if its just when climbing hills that bothers you, check into adding some Redline Water Wetter or similar to the coolant.

 

I use my obd reader to get these numbers. I do wonder about the tune being lean as a possibility. Maybe I'll look in to o2 sensor and gauge

 

I have no idea if the radiator is the problem, but it's pretty easy to remove. Comes out the bottom with the intercooler hanging on it.

 

UPDATE:

I went big and replaced the coolant cap, heater core, and the radiator, got an OEM thermostat in there too. Did a full flush, put in 50/50 pentofrost NF. Burped the system a couple times through heat cycling. Then I took it on a longer, harder test drive and it successfully kept temps below 225!!
I was so excited. Until I opened the hood and saw that the fluid had boiled out of the reservoir like before.
I'm at a total loss now. I guess all I can assume is that the head gasket is blown in such a way that only under serious boost it pressurizes the cooling system? In which case it's just time to push this POS off a cliff and say goodbye most likely.

 

when did you last change the PCV system on the volvo ? if these get blocked it can cause a fair few problems