Dash Thump?

My 98 Ranger (4L OHV) started having a muffled rhythmic thump mid dash. Behind the radio/heater controls etc. Very confident it is not from the engine compartment. Also, not every trip and only seems to be during the cold temps (<20F). It does it for less than a minute or so when it is starting to warm up. If I sit and idle for 5-10 minutes to warm things up, nothing then I'll drive a few miles and stop at a light and I'll hear the thump thump thump in the dash.

I'm beginning to think it may be the radio since I have a real loud pop when I turn it on in the cold weather. I haven't tried to shut off the radio when it is occurring. That will be my next test if I can repeat it. Like I said it is muffled and doesn't happen all the time.

Anyone? :scratch:

sounds like cooling system thump due to trapped air or steam in your heater lines. There is a tsb on it. I had the same issue with my 96 4L ohv. Has your cooling system been modified? does your temp gauge fluctuate?

SensRanger said:

sounds like cooling system thump due to trapped air or steam in your heater lines. There is a tsb on it. I had the same issue with my 96 4L ohv. Has your cooling system been modified? does your temp gauge fluctuate?

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Thanks for the suggestion. No modification to cooling system. Strangest thing is it only did it 3-4 times when extremely cold. Can't replicate it now. May have to wait til next winter and see if it happens again. I do have a flush planned within a few weeks.