Hi Spook,

Yes, Regina got the thermal fan switch in the rad, and yes, it's safest to also secure it with zip ties or wire through the fins and around the plastic tank. As I mentioned, the LH 2.4 system got a two speed fan and that thermal switch could no longer be used. Originally Volvo made the rad without the plug hole, then went for a universal fit using a plastic plug that you push into the rubber grommet, or you can simply insert an old thermal switch and leave it disconnected. Note that the LH 2.4 B230FT with intercooled turbo uses a slightly different sized rad and never came with Regina, but the rad often still comes with a hole to plug.

The rad cap on the expansion tank is indeed the safety valve, but you still need to be aware of the weak points that can fail under continual stress and sudden high pressures. I've had one rad plug blow out on the highway in our 940 LH 2.4 NA. Whether or not the cap was also relieving pressure at that moment is uncertain. I replaced the plug and secured it. Next to blow a few weeks later was the heater valve. It was the 20+ year old original one, which I was quite aware are known to fail, so my fault for not replacing it sooner. I replaced that with an unused, but older MTC valve of the same original half metal, half plastic design and it blew open on the next highway trip. Okay, woah, maybe something's not normal here! I was starting to get worried the next thing to go might be the heater core, which was still the original in this car (the one 940 and one 740 heater core I've had to replace is an exercise I'm in no hurry to repeat). It was then I started to investigate closer. Although the coolant looked normal and there was no smoke in the exhaust, I suspected a head gasket leak, which was quickly confirmed by one of my Volvo indies. Idle the car with the rad cap off until the thermostat opens and if it suddenly boils over then it's the head gasket (With the B230 engines you should be able to idle almost indefinitely with the rad cap off).

As long as we're on the topic of cooling system pressure and weak points, here's from some of my old notes that I've posted here before:

The coolant expansion tank caps used are as follows:
- grey = 150 kPa (22 psi) superseded by the green cap
- green = 150 kPa (22 psi) standard issue for all 700/900s
- white = 100 kPa (15 psi) uncommon (used in one of the 240 variants in Europe)
- black = 75 kPa (11 psi) standard issue for all 140/240s

It's always best to use genuine Volvo or at least a reputable OEM brand. The green caps provide for optimal engine operating conditions in 700/900s. Some people believe the lower pressure (240) black cap doesn't stress the plastic sides and fittings of the rad tank as much, especially in a hot turbo engine compartment and especially as the rad ages. With that thinking in mind I've decided the trade off is worth it and use a black cap in my 940 turbo, but have kept the green cap in my 940 NA. Remember that the higher pressure caps prevent system boilover in high temperatures and allow higher engine operating temperatures, important for good fuel economy.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now