Mercruiser temp gauges not working

ian38_39

ian38_39

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I have twin mercruiser 3lt petrols in my new boat that are less than 2 years old, during sea trials it was noted that the port engine was running a bit cold, now the boat is on hard standing it is obvious why, both gauges are still reading the same as on the trial.
has anyone got any ideas. the gauges were new with the engines
 
Is this reading the same with the ignition on.?? I only ask as on my Volvo petrols the temperature guages stay where they were when the ignition was switched off, ie running temp. They then start reading again when ignition switched back on and so only then will they go back down to cold...?? Just a thought....Iain
 
I had this on mine - first thing to suspect is the temp senders - screw-in, power and earth contacts on the ends of them, forward top of engine on my 5.0's, about a fiver a chuck.

Next thing - check the thermostats. Engines will run without stats (as I discovered when I bought my boat, previously owned by a Mercruiser dealer /forums/images/graemlins/confused.gif) but then they constantly run "rich" and never get up to operating temperature so you'll be washing the oil off like that.

Let us know how you progress.
 
temp gauges havn't moved since sea trials and have run them for flushing and winterising. port gauge is just off cold and starboard is in normal range. will try the temp senders see if that makes a differance, have just realised I won't be running them again till the weather warms up though so may be sometime before I can see if it works
 
Still could be worth looking for corrosion on the two contacts, though. I seem to recall that you can test them by shorting the contacts and the gauges should swing instantly to the right (i.e. overheating), but I may be wrong......
 
Mercs VDO guages do the same as Ifraser,s volvo's.

Make sure you have sufficient waterflow, ie impellars are not shot, temp senders don't read in air!

You can determine this by servicing the legs before winterising.

You will be winterising to protect from frost damage I hope?, so need to run those engines again much before any sub zero temps, don't leave it & hope for the best come spring, it could turn out very expensive if not done!!.

Just read your original post, you have winterised,Dohh......... I must learn to read properly.. have a good christmas /forums/images/graemlins/blush.gif
 
You can check the gauge by earthing the sender wire to the block, the gauge should read full deflection one way or the other. Have you checked if the port engine actually has a thermostat fitted or it could have just failed in the open position.
 
Just had the same problem with my pt 7.4l Merc petrol. I changed the sender (cheap), but no change. Took it to the yard and they fixed it, but I haven't had the bill yet so don't know what they did. The Merc manual does tell you how to troubleshoot, but mine's on the boat. I couldn't get to the back of my gauge, so I left it to the experts. It doesn't look like a new gauge, BTW, unlike the tach which was playing up. New one: $620!!! +fitting+tax.
 
Havnt yet serviced the legs but do have impellors and gaskets for the job, was going to do this before winterising but getting the tank out of the boat took over as the most important job, winterising at the moment consists of purely a drain down of domestic water and flushing and draining the block and exhaust manifolds, will try and get them fired back up though to fill back up with antifreeze to prevent the corrosion looks like they will be running out of a petrol container though.
assume impellors are working as there is plenty of water being passed through the exhaust.
 
ouch, tacs are working thankfully, the gauge is new and I can drop them out so will have a check through of the wiring, the engines have only done 40 hrs but they were installed in august 2004 she was on hard standing all this year so there could be some corrosion somewhere.
 
I forgot to mention that I had a similar problem w/stb readout earlier this year and I managed to spray CRC electronic cleaner on the back of the gauge and it did the trick. The pt didn't respond to that. Yours may be due to slight corrosion, too.
 
Re: fuel tank

Had a hole in the tank (Petrol) last winter, Know the feeling of urgency.

I had problems having it repaired, unable to find anyone willing to tackle an alloy tank that was contaminated with fuel!!!.

After much searching & speaking to manufacturers etc, it was apparent that all they wanted was to supply a new one.

Found a firm in Bath that Vulcanise the existing tank with a franchised product named tank RE-NU, they do auto, marine & industrial tanks as long as they are under 6ft long.
There are numerous franchises up & down the country.

Once done they give a lifetime guarantee, price was very very good, £180 inc collection & delivery by courier for a 200ltr tank.
 
Re: fuel tank

very fortunate to find a friendly MD of a company specialising in s/s petro chemical tanks who is getting a new 65 gal fuel tank and a 20 gal holding tank made for me for the price of the stainless and a drink for the lads, kills 2 birds with one stone as I was realy struggling to find somewhere for the holding tank
 
Re: fuel tank

Great!

Must admit I tried the local firm stainless route without success.
Was told stainless was too strong for fuel tanks, they tend to split at the seams rather than flex(oppinion from them) & that all new stainless tanks require pressure testing & CE marking?

After finding the vulcanising alternative I did'nt persue this further, but it did sound daft at the time.
 
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