Cooling/Heating system questions

Issues pertaining to the TGB/C30X series engine and driveline issues
Post Reply
Posts: 73
Joined: Sun Jul 10, 2011 4:24 pm

Cooling/Heating system questions

Post by Doccers » Sat Nov 08, 2014 9:07 am

Hoya, guys!

Got a question on the cooling/heating system on a C303/304:

I stopped getting heat to the front heater (99% sure it's the adjustable valve that the rotating knob on the dashboard controls - I think I've located where it is, and the hose going to it is warm, the hose going beyond it is not), and I confirmed I'm still getting heat to the rear heater.

The odd thing is, the day I was driving it and discovered the heat wasn't working, not only was it blowing cold air, but the temperature gauge was climbing 3/4 of the way up before the thermostat would open. Appeared to operate normally aside from that, but it made me worry. When I turned the blower off, after a minute or so the temp gauge went down and indicated the normal 90C. front blower back on, temp rose to 3/4 on gauge. Back off, back to 90 C.

Looking at the circuit, I cannot figure out for the life of me how the hell that would happen - Coolant is good, no blocks in radiator (radiator new, coolant new, woo!), thermostat functioning correctly.

How would the front blower (particularly when the valve is closed so no hot water is flowing to the front heater core) cause that dramatic of a change in temperature readings?

The only thing I can think of is electrical fault - the extra load from the blower motor running may be playing havoc with the electrical temperature sender?

At the moment I'm stuck scratching my head, so I figured I'd toss this out here and see if anyone can see what I'm missing.

Thanks, all!

User avatar
United States of America
Posts: 822
Joined: Thu Oct 06, 2011 5:25 pm
Location: Mount Vernon WA USA

Re: Cooling/Heating system questions

Post by Haf-e » Sat Nov 08, 2014 11:43 am

If the temperature goes up and down quickly with the fan on/off - then I would suspect electrical - often it is a poor ground connection that is the culprit - try connecting a heavy ground cable (such as a jumper cable) to the body of the fan to ground/chassis while its running and see if the gauge changes... also check on how the gauge gets ground - some do it through the mounting bracket.

I know nothing about the Volvo specifically...

1971 Pinzgauer 710M

Disc Brake Conversion Kits for 710 and 712 Pinzgauers

Post Reply