Calling Volvo experts - N12 cooling

Re-read all the posts, by the problem being when the thermostats are closed or closing would suggest the bypass system could be at fault. Not familiar with Volvo systems, can be either internal in the thermostat housing or extenal with hoses.

Very interesting reading, 60 PSI in a cooling system seems way too high. Do trucks not have the little hole in the thermostat that lets air escape?

I also have an interesting story, Perkins 4.236 in a boat. never got up to its proper temp despite new thermostats. Had closed cooling, which was a heat exchanger that bolts on top of the thermostat housing where the hose normally goes off to a radiator in a road version. Drove me nuts until I figured out that it had rusted away the hole in the lower surface of the heat exchanger to the extent that it was a little larger than the thermostat outer diameter. As soon as flow started the thermostat just lifted through the hole a little and was completely bypassed. Would have spotted it earlier, but in this boat you could only lift it a few inches as it hit the cabin sole above unless you completely dismantled the woodwork. Made a stainless plate with appropriate hole to sandwich in between and Voila!

Depending on the style of thermostat and engine design you can overheat it it with the thermostat removed.
Bypass systems are just that and with the thermostat removed the coolant can bypass the radiator and just keep getting hotter.
Additionally fast coolant flows do not pick up heat from the block/head surfaces too well and they can be subjected to coolant temperature shock on down hill runs when it overcooling can occur (non bypass systems)The old trick with non bypass systems was to gut the thermostat and leave the body in place to maintain a little back pressure

Silly question ... But .... How do you fill the system ... Through the header tank or through the fitting on the bottom radiator hose?

ok well definitely not saying it's not the bypassing, apart from the pressure spikes while revving. Someone else mentioned a blocked bypass but I couldn't immediately see one. It's got a big single thermostat with no bleed hole in it, where do I find the bypass system (if it has one) on this late model N12?

Ok lets get back to basics. The original problem is blown coolant hoses. First of all, no blockage and no water pump is going to create 60 psi. Secondly, there wont be a thermostat problem if the engine is running at the correct temperature.

Wedgetail, may I suggest trying the leakdown test, since your coolant test has already revealed a combustion chamber leak. If you want to try an old school approach, try fitting some of that clear, reinforced high temp hose in place of your top radiator hose. Fill the system, leave the cap loose and take it for a run. Then look at the hose with the engine running. If it has a leak, you will see bubbles. At the end of the day, the leak down test is the correct procedure, and if you take it to a Volvo dealer, this is the test he will do.

Yeah sure it's not going to create the pressure so it's not going to be the main cause. But if the bypass is working how can it build up beyond the rad cap release pressure?

I will do the leakdown test. I assume I need an injector puller, do you know what sort?

Silly question ... But .... How do you fill the system ... Through the header tank or through the fitting on the bottom radiator hose?

Through the bottom fill port on the rad

Don't have a fitting so put a ball valve on and use a hose and funnel and pour from the roof

Wedge, I'm going to suggest something so silly you will think I have my head in the clouds, but I had something very similar once before.

These hoses that blew off, did you put the gauge on these and where do they run to? Is an oil cooler involved? I'm just wondering if a blockage in a coolant passage, either in the block or oil cooler, has ruptured an oil passage in the cooler? It is possible that the blockage is not complete and some oil is escaping into the coolant, which is showing up on that coolant test. That pressure reading of 15 at idle and 60 at full noise just sounds very much like engine oil pressure to me. If you watch the gauge when you switch the engine off, does it maintain that pressure, or does it fade out in a few seconds?

This would explain the localised pressurisation and why the cap does not blow off. I know its a bit "out there" but it sounds like your grasping at straws.

Could you put up some photos of these lines and where they run, and your gauge setup. It might inspire a new line of thought from someone...

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And this...

Wedge, I'm going to suggest something so silly you will think I have my head in the clouds, but I had something very similar once before.

These hoses that blew off, did you put the gauge on these and where do they run to? Is an oil cooler involved? I'm just wondering if a blockage in a coolant passage, either in the block or oil cooler, has ruptured an oil passage in the cooler? It is possible that the blockage is not complete and some oil is escaping into the coolant, which is showing up on that coolant test. That pressure reading of 15 at idle and 60 at full noise just sounds very much like engine oil pressure to me. If you watch the gauge when you switch the engine off, does it maintain that pressure, or does it fade out in a few seconds?

This would explain the localised pressurisation and why the cap does not blow off. I know its a bit "out there" but it sounds like your grasping at straws.

Could you put up some photos of these lines and where they run, and your gauge setup. It might inspire a new line of thought from someone...

It does have an oil cooler I'm pretty sure, but I've had the coolant out about three times (back when I kept soldering up the rad) and never a trace of oil. Also I got a coolant sample done by Westrac SOS and nothing was flagged (coolant bloke there said I'd have to send more samples to find a rise in NO3 for combustion gases, hence the Tee Kay). You're right about the oil pressure, that's about where the oil pressure is I think which is very coincidental. I never thought to compare them, I will when I get a chance to get back to her. I can't remember if pressure fades quickly or stays, I think it might fade quickly.

I'll post a few photos of the plumbing, hopefully can get back to it on friday - carting hay tomorrow.

The hoses that blew were a heater hose (above rocker cover), maybe a tranny cool (was under the back of the cab), and another small accessory hose, can't remember that one. But a seem in the rad keeps leaking - above the bottom fill port then after I soldered it leaks after another 3-4 trips. Haven't put a gauge in those areas, but it's funny the rad keeps leaking as that port is where I put a gauge and it never went above cap pressure (of course).

I was sure it would be a blockage at the beginning until I found the pressure thing. But maybe it's a combo...

That manual is gold, I heard they were unobtainable. Bought it. Leakdown tester loos good too, what sort of injector puller do you recommend and do you need to recut the seats when reinstalling after a test?