• Registered: 2009-08-20
  • Posts: 24

Topic: Pre-heater tubes

When I converted my '75 std. bug from EFI to carb. had no place to hook up the pre-heater tubes. I had a VW mechanic drill through the exhast manifold and weld on pipe nipples to connect the pre-heater tubes. Now the tubes get VERY hot and the intake manifold also feels unduly warm. Anyone know how hot these tubes should get? I used flexable copper tubing to make the connection between the new nipples and pre-heater tubes. I thought if they were running too hot, I could crimp the tubing a bit to reduce the amount of exhaust going to the tubes. Could too much heat cause any damage to the engine- valves, etc.? Thanks, Ken.

  • hank
  • Member
  • Offline
  • From: British Columbia Canada
  • Registered: 2004-03-30
  • Posts: 430

Re: Pre-heater tubes

There is a restrictive gasket for that- same size on the outside but with a small hole in center
used on one side

'57 bug "BlackBerry"
'58 type261 single cab "Ruf"
'86 vanagon syncro "Syncro da Dr.Mayo"
and way too many project waiting
  • From: somewhere over the rainbow USA
  • Registered: 2006-07-26
  • Posts: 1,889

Re: Pre-heater tubes

The exhaust gets real  hot but if you think to hot, it would be best to put in a restricter in line to help block flow if you have no provision for what Hank mentions.

burrhead

A wise man makes his own decisions, an ignorant man follows public opinion.
  • Registered: 2009-08-20
  • Posts: 24

Re: Pre-heater tubes

Thanks for your comments. Can't use a gasket 'cuse it's a 'jury rig' - no flanges just a tube connected between the welded-on pipe nipple (to the exhaust manifold) and the preheater tube with the flanges cut off. I realize there's other ways to restrict the amount of exhaust gases passing through the preheater - just crimping the (copper) tubing might be one. I'm just wondering how hot is 'too hot' and whether any damage might result from the 'too hot' intake manifold. Maybe this is too obscure! Thanks again. Ken

  • Registered: 2009-06-25
  • Posts: 558

Re: Pre-heater tubes

It's hard to determine the "correct temperature" unless you take a new stock system and measure the center peice of the intake manifold, then use that for comparison. You have to measure after the same amount of run time, since the temperature will keep going up under some conditions.

Paul