Re: 3126 heater element do you need it



Just thought I would post an update on this for anyone that might be interested.

Had an issue onboard last week where we had a significant smell of rubber smoke coming from the engine room.  We shut everything down and returned to our marina on 1 engine.


The upshot was that on the Port Engine (the one that we were NOT experiencing the voltage drop issue), an electrical cable in the engine's junction box had come loose and moved itself across to the the other pole of the relay, thereby making the circuit live.  It turns out that this is the relay for the heater elements.  This lead to overheating of the relay and effectively melting of the rubber and plastic at the top of the relay housing.


I suspect that this cable had been loose for some time, hence the heater elements not operating on that engine.  This would be consistent with Dave's advice.


To resolve the issue we purchased a new relay from Cat and replaced it yesterday.  After installing this we saw the same voltage drop that we had seen on the Starboard Engine and was the original purpose of my questions.  Again consistent with Dave's advice.


In addition I have added into the switching line for the relays on both engines a second manual switch.  Effectively now I can manually switch ON or OFF the heater elements to suit.  Frankly in our climate in Australia they are of little value, and the Port engine had been operating fine without them for as long as I can remember.


Cheers and thanks for the earlier advice on this issue.




Re: 3126 heater element do you need it

Thanks Dave

I will take your advice and put a multimeter on the other engine.

It just strikes me as odd that they would design it to exert such a load that it draws the battery down to 10.5v repeatedly.  This repeated load on the battery is quite damaging to them.  BTW the batteries were replaced last year and are good quality N200 size batteries (2 of them).

Thanks again


Super Contributor

Re: 3126 heater element do you need it

Your intake heater is working correctly. The heater is supposed to be ON when the ignition switch is first turned on. After engine starts, heater cycles off and on until coolant temperature reaches 120F. The intake heater draws almost 100 amps and it's normal for battery voltage to show lower than 12 volts right after engine startup. The heater is used to reduce white smoke on startup. It sounds like the heater is not working on the other engine. The intake heater relay or timer could have failed. The heater element doesn't often fail.

Re: 3126 heater element do you need it

I have been doing some homework on these heater elements as I am experiencing a significant voltage cycling issue upon start up.


In my boat I have 2 Caterpillar 3126 diesel engines.  I am experiencing a voltage issue after starting.  The issue is that voltage sits around 10.5v, then cycles up to around 12v, then back down to 10.5v.  This cycle occurs every 15-20sec for about the first 5-10 minutes of run time, when it then climbs to a normal charging voltage around 14v.  This is only an issue with 1 of the engines, the other 1 is fine.  I have checked these voltages with a multimeter, rather than just relying on the gauges.


This is obviously indicating that something is drawing heaps of power in that first period of time.


I have identified what I believe is causing this draw of power.  Attached is a photo showing the top of the engine.  There are 3 parts evenly spaced along the top of the engine connected by an electrical cable.  I disconnected them and started the engine.  Engine started fine, no voltage issue.  I reconnected them progressively 1 at a time, restarting the engine after connecting each one.  Issue reappeared after connecting the last 1 (the one to the far left of picture).





My questions are:

  • Are these the heating elements?
  • Are they easy to replace?  Can someone perhaps provide a part number for them?
  • Given the engine started fine without them, are they the sort of thing I could just disconnect and forget about?

Engine serial number is 8NM01861.


The boat is in Sydney, Australia which is a relatively warm climate.


Cheers and Thanks



Trusted Contributor

Re: 3126 heater element do you need it

Most pleasure craft owners that I have dealt with in SO CAL always have atleast  an engine block heater like a KIMHOTSTART unit... I would suggest a block heater yes.  The benefits would limit condensation buildup by keeping the block warm in varying temp climates, but the air induction heater is probably not needed if you have a block heater.


Additionally, the blockheater would lessen the startup smoke and assist in quick starts possibly.  Just some thoughts for you.  And yes, removing the A/C core can be cumbersome depending on the application and access in the vessel.  


I would consult with a local dealer just to make sure - the SO CAL dealers are quite good with basic consultations on service needs to give you an idea what your potentially getting involved in.  


3126 heater element do you need it

I had a short in the heater elements that sit on the top of the engine

my mechanic told me they were to heat the air coming into the engine and that it was a big job ( to take the aftercooler apart?) to replace them 

he said that being in southern california where the boat is never started in less that 50degree temp that it is not necessary to have them working


Is this a correct statement?

and how long should you run your engines before putting them under load?

(I usually will run the boat at troll speed 750rpm untill the temp comes up the run slowly up to 1500rpm until the temp goes to 170)