Bringing a 740 back to life

[Laird Scooby]

Originally Posted by Challo

Since the MOT managed a few local trips, but today took the old girl for a longer drive. Had the tracking done this morning, but it needs to go back as it pulls slightly to the left. Also there is some vibration at motorway speeds so will get them to check the wheel balancing.

Got back and noticed two issues to check on:

1. Start the car and it idles sub 1k rpm, but once up to temp and start in traffic in park it clicks up to 1100-1200k rpm. Any particular reason for this?

2. Coolant leaking inside and outside the car. Inside it’s the heater control valve, but I have the parts for that. Outside it’s dripping from the pipe which connects to the expansion tank. Going to replace that pipe, but not clear which one I need.

Checked PFV and they only have top or bottom hoses. I think I need top hose but unclear https://www.partsforvolvosonline.com...oducts_id=3950

Wheel alignment can be a pain to get right Chris, especially if the steering wheel has ever been removed for whatever reason. From the straight ahead position, you should have 1 3/4 turns to each lock or a smidge over but it must be an equal smidge both ways. If you haven't, they haven't aligned it with the rack central, just with the steering wheel in the straight ahead position which will cause it to pull.

You need 8mm bore heater (or fuel) hose if memory serves if it's the small hose from the expansion tank to radiator. If it's the other one, i think it's 19mm bore heater hose but remove the hose from the bottom of the tank and measure the size of the stub, will either be 16 or 19mm on the smooth part of it (don't measure the barb diameter!) so get whatever size it is.
The larger of the two hoses goes from the expansion tank to the bottom of the rad, the smaller (breather) hose goes to the top of the rad.

Thinking about it, you may not have a separate spigot for the small bore breather hose on the expansion tank, would help if you could post a pic of which one it is and how it's attached to the tank.

https://www.partsforvolvosonline.com...?cPath=608_683

A few options there to choose from!

Because you're losing coolant, you will have airlocks in the system, most likely where the temp sensor is in the head for the ECUs - this will cause a high idle. There could be other causes as well but you need to get the leaks sorted before going anywhere near those possible causes.