revs dip when fans cut in

[Punboy3]

Hi everybody - anyone point me on the right direction with this?

When my fans cut in they cause a jolt to the engine and a temporary drop the revs. This is making sitting in traffic an uncomfortable experience. Also, I noted that when the fans cut in at 90 degrees the gauge jumps to close to the red zone. When the fans go off, it jumps back to between 90 and 93. The rapidity of its jumping around suggests some sort of issue, but what with?

All suggestions graciously received...

[ClassiChimi]

Look on the Chim forum for a thread " Amps Alternators and rad fans"
Sheds some light on spikes and electrical issues related to the sudden increase of power required to turn fans on especially at tickover.

Edited by ClassiChimi on Thursday 1st December 09:05

[Colin RedGriff]

I had a similar problem.

In my case it was an earthing problem. The fans earth to a bolt on the front o/s chassis rail under the rad, I removed the bolt and cleaned up the earth rings and added some copperease. I also found the earth bolts on either side of the transmission tunnel weren't tight, again I cleaned and tightened them both up.

This cured my problem

[Englishman]

Agreed, most likely to be an earthing issue in my experience.

[blitzracing]

There is an input on the ECU that TVR have not used to eliminate this type of issue- it simply lifts the idle a bit as the extra electrical load kicks in and loads up the alternator. It would need a relay and a bit of wiring onto the ECU to make it work, but the option is there.

[Punboy3]

ClassiChimi said:

Look on the Chim forum for a thread " Amps Alternators and rad fans"
Sheds some light on spikes and electrical issues related to the sudden increase of power required to turn fans on especially at tickover.

Edited by ClassiChimi on Thursday 1st December 09:05

Many thanks for the tip.

[Punboy3]

Thanks everyone for your pointers on this.

[ClassiChimi]

Punboy3 said:

Many thanks for the tip.

Check those earths first

[Punboy3]

Colin RedGriff said:

I had a similar problem.

In my case it was an earthing problem. The fans earth to a bolt on the front o/s chassis rail under the rad, I removed the bolt and cleaned up the earth rings and added some copperease. I also found the earth bolts on either side of the transmission tunnel weren't tight, again I cleaned and tightened them both up.

This cured my problem

I agree - earthing issues cover a multitude of sins. Would hope my earths were clean seeing that I'm only a year into a body off chassis restoration, but you never know.

[Colin RedGriff]

Punboy3 said:

Colin RedGriff said:

I had a similar problem.

In my case it was an earthing problem. The fans earth to a bolt on the front o/s chassis rail under the rad, I removed the bolt and cleaned up the earth rings and added some copperease. I also found the earth bolts on either side of the transmission tunnel weren't tight, again I cleaned and tightened them both up.

This cured my problem

I agree - earthing issues cover a multitude of sins. Would hope my earths were clean seeing that I'm only a year into a body off chassis restoration, but you never know.

Mine too - I think the main issue was that they had come loose following a body lift.

[Sardonicus]

ClassiChimi said:

Check those earths first

This ^. Earths/Grounds should always be your 1 st check in these situations