Over temperature alarm

[Kevin Saunders]

Read a recent post about changing the fan belt and a lot of discussion ensued about the damage that can occur in a short time due to belt failure.
Is there some sort of alarm to warn of belt failure or head/cylinder over temperature available?

[richde]

the alternator light

[Kevin Saunders]

By the time you notice the alternator light it may be too late - I am talking about an audible alarm.

[rnln]

your eye

[kodioneill]

it would be a simple matter to install a buzzer using a relay with the alternator light circuit.

[Grady Clay]

Kevin,

Good idea.

Porsche found this an issue with the 908 where the alternator and fan were driven separately. This became common on many other race engines.

The 908 (and later) uses an air pressure sensor measuring the pressure under the fan shroud. When the pressure drops below an adjustable threshold, it trips a large warning light on the dash (an audible is implacable on an open race car).

I think some later 911s (993?) have a fan belt idler with a broken belt warning sensor.

The 911 engines in my race 914-6 have gutted alternators. The housing only supports the fan. The engine runs off a large battery. I use this 908 pressure sensor to warn of a broken fan belt. I have the pressure adjustment set so the light is on at lower (non-race) rpm – same with the 40 psi adjustable oil pressure switch (771 part). All the warning lights come on below about 4500 rpm at race temperatures. This serves as a regular test of the warning function.

Best,
Grady

[Kevin Saunders]

Thanks Grady/Kodioneill.

I suppose regular changing the belt would be the answer but if there was a simple solution such as Kodioneill suggested it would be worth it for the peace of mind. Perhaps someone could draw up a wiring diagram for the alternator signal solution - I am electonically challenged.

1977 911S coupe
1969 TR6
British Columbia

[Jack Olsen]

Can the 993 belt sensors be retrofitted to earlier motors? I know I have on added to my 964 motor. It's a simple pulley on a lever that activates a switch if the belt suddenly isn't there.

[Kroggers]

Can you supply some pictures Jack. Sounds like all it needs is a mounting bracket made?

[kodioneill]

after looking at the schematic, if the alternator stops working the fuel pump relay will open causing the engine to shutdown. so it looks like they have this one covered.

[Kevin Saunders]

Would this apply to my 77 2.7 engine?

[Miguel Antonett]

Guys, if you can't see the RED alt light on the gauge coming up you probably won't hear a buzz either... But a double warning might not hurt - I guess - Just another guizmo...

[RoninLB]

Originally Posted by Jack Olsen

Can the 993 belt sensors be retrofitted to earlier motors? I know I have on added to my 964 motor. It's a simple pulley on a lever that activates a switch if the belt suddenly isn't there.

this should be the unit. I got it when an engine was being race setup. I never installed it as I figured latter on that a marine alarm pack would be an easier install with more options than just a voltage alarm. There are a few different marine systems out there for not a lot of $. If interested google "West Marine"

Personally, after a day's drive exceeds 10 hours I'm not exactly concentrating on picking up on a small dash red light. It's no prize either with a clear head in calm driving.














ps: the wheel slides close in to the housing when layed against the belt. It's spring loaded and will pop back out as in pic. I guess "wheel out" closes the circuit.

[Rot 911]

Originally Posted by kodioneill

after looking at the schematic, if the alternator stops working the fuel pump relay will open causing the engine to shutdown. so it looks like they have this one covered.

Are you sure about this. I believe that if the ignition switch is in the on position and the battery still has a charge the fuel pump will keep running.

[Miguel Antonett]

Are you sure?

Does this apply to the 930's also?

I have ran my engine "very briefly" without a belt checking/confirming alternator bearing noise... without a blimp; and could have ran the engine until burning it.

It would surprise me if the 911 and 930 have different wiring on this area.

[kodioneill]

Originally Posted by Kurt V

Are you sure about this. I believe that if the ignition switch is in the on position and the battery still has a charge the fuel pump will keep running.

after looking closer i was wrong. i mistook d- for d+ on the alt. i apologize.
it looks like the air sensor plate controls the fuel pump relay power.

sorry kevin for the misinformation.

[Kevin Saunders]

Thanks Kodioneill - looks like something Porsche should have adopted. I looked at the West Marine site and it looks like the engine monitoring systems are aimed at liquid cooled engines.
Still looking for a reasonable solution - perhaps the signal from the alternator light?

1977 911S
1969 TR6
British Columbia

[RoninLB]

Originally Posted by Kevin Saunders

I looked at the West Marine site

I found a Cole Hersee electronic alarm. It would have to be triggered by the idiot light wire. There are other alarms so I'm just guessing the electronic alarm would need less amp to trigger? Alarm sounds at a minimum of 90dB. And Cole Hersee is considered marine quality.

If you want to investigate it's Cole Hersee # 40212 and costs anywhere between $40-$50us.

This unit has me interested. The first thing I'd do is call or e-mail Cole Hersee and see if it's doable.

If you investigate and if possible let me know

[Porsche-O-Phile]

Originally Posted by Miguel Antonett

Guys, if you can't see the RED alt light on the gauge coming up you probably won't hear a buzz either... But a double warning might not hurt - I guess - Just another guizmo...

Seriously. Train yourself to scan your gauges occasionally.

Back when I was flight instructing I gave a BFR (Biannual Flight Review) to a guy in his own Mooney airplane. I gave him a busy workload setting up for a landing in the traffic pattern and popped the landing gear motor circuit breaker midfield downwind. This guy somehow missed:

- a warning horn
- a warning light
- a warning SIREN when the throttle was pulled back with the gear still up
- and called out "gear down, 3 green [lights]" when none of the "gear down" green lights were on.

Point is you can't count on electronic gizmos to save you or even get your attention when things get busy - you need to actually scan them and train yourself to pay attention to them. Otherwise you'll see and hear what you expect to see and hear.

[Miguel Antonett]

Amen!!!!!!!!!!