Coolant temp sender never going about 40 deg C

[fergycool]

I've had a few issues with the temp sender on my starboard engine. The original sender was stuck at 80degC as soon as you turn on the engine. I replaced the sender and now it never goes above 40degC! When you start the engine it moves slightly. After about an hour of running it's moved slightly closer to the 40degC mark but never any further.

I've tested the resistance of the temp sender and it's fine. When connected at the gauge the resistance between the sender and -VE posts behind the gauge is 3.7kOhms. The same as the sender terminal and the engine block.

If I disconnect the sender the gauge is at zero. If I short out the sender and the -VE it goes to maximum deflection.

With a separate identical sender the gauge works. When I heat the spare sender the gauge rises. Also when heated to 50degC the sender's resistance drops to about 1.5kOhms.

So the only possible explanation is that the sender is in a part of the engine that never rises above 40degC! Could the thermostat be permanently open? Certainly with an infra red thermometer no external part of the engine goes much about 50degC.

My other engine rises to close to 90 degC after about 10 minutes of running then drops down to about 80degC and never changes much from there (I assume the initial high temp is before the thermostat opens).

The engines are indirect raw water cooled Perkins 4.270s.

Cheers
Chris

 

[elton]

Put the thermostat in a pan of water with a thermometer and heat it. You'll see when the thermostat opens and closes. Otherwise, swap the port and starboard thermostats and test.

 

[fergycool]

Put the thermostat in a pan of water with a thermometer and heat it. You'll see when the thermostat opens and closes. Otherwise, swap the port and starboard thermostats and test.

Thanks I'll give that a go!

 

[vyv_cox]

Before going to the trouble of swapping thermostats, put your hand on the engine close to the sensor reading 40C. If it is a genuine figure you could hold your hand on it all day. If 'Ouch' is the result, the sensor is faulty. Have to say it does sound like a thermostat problem. My BMC engine took all day to reach a little more than 100F (40C), I then discovered that not only was there no thermostat in there, the botched construction made it impossible to fit one.

 

[fergycool]

Just removed the thermostat. It's a mess! Fairly corroded and stuck open! Thanks for the pointers!

It's a fairly old engine. I'm assuming that the diameter is the only critical dimension? As long as it fits height wise? I guess a motor parts factor could supply one?

 

[VicS]

Just removed the thermostat. It's a mess! Fairly corroded and stuck open! Thanks for the pointers!

It's a fairly old engine. I'm assuming that the diameter is the only critical dimension? As long as it fits height wise? I guess a motor parts factor could supply one?

Not clear if its indirectly cooled or raw water cooled ... you say, "The engines are indirect raw water cooled"

If the engines are raw watercooled a car type thermostat will open at too high a temperature. and even a modern thermostat may be too high for your engine even if its indirectly cooled
Check your manual get a thermostat that opens at the correct temperature and is also the correct type regarding any internal bypass arrangement the engine may have.
In other words get the right one!

 

[fergycool]

Not clear if its indirectly cooled or raw water cooled ... you say, "The engines are indirect raw water cooled"

If the engines are raw watercooled a car type thermostat will open at too high a temperature. and even a modern thermostat may be too high for your engine even if its indirectly cooled
Check your manual get a thermostat that opens at the correct temperature and is also the correct type regarding any internal bypass arrangement the engine may have.
In other words get the right one!

Sorry it's indirectly cooled. The manual does not say much. I have a workshop manual, which I thought may discuss it, but it does not.

 

[VicS]

Sorry it's indirectly cooled. The manual does not say much. I have a workshop manual, which I thought may discuss it, but it does not.

My guess is that the opening temperature will be around 80C. The technical specs in the manual should confirm but the existing one(s) should be marked with the opening temperature and possibly also the fully open temperature,

I'd expect it to also incorporate a bypass valve in which case it will be important to obtain the correct part.

 

[vyv_cox]

My guess is that the opening temperature will be around 80C. The technical specs in the manual should confirm but the existing one(s) should be marked with the opening temperature and possibly also the fully open temperature,

I'd expect it to also incorporate a bypass valve in which case it will be important to obtain the correct part.

From memory the one I bought from a tractor supplier to fit the housing on my BMC 2.2 indirectly cooled engine was marked 82C.

 

[fergycool]

From memory the one I bought from a tractor supplier to fit the housing on my BMC 2.2 indirectly cooled engine was marked 82C.

The starboard engine runs up to about 85degC after about 20 mins of running then drops down to about 80degC and stays there more or less consistently.

So assuming the starboard temp gauge is accurate I would guess 80 > 85degC is indeed the range.

 

[fergycool]

Update: I could not find the original thermostat anywhere. However, the one from the Perkins 4.236 (which I think came after my engine:4.270) is the exact same height and diameter (54mm). The opening temperature being 84degC. It does not have a collar to block a bypass channel. So I guess this is far from ideal. But considering that channel has been open for some time as the thermostat was corroded and stuck open I guess it's an improvement!

I ran the engine last night in idle for 30 mins and the temperature did rise. It rose to about 50degC on the dashboard thermometer. An infra red thermometer pointed to the engine block, close to where the temperature sender is, showed 60 degC. Previously this never rose above 40degC even all day!

I'm off for few hours run this afternoon and let's see how it goes!

Many thanks for the feedback and advice.

 

[fergycool]

After two hours cruising the engine block temperature was 84c, the header tank was 84c but the thermometer was 60 ish. I guess the thermometer is mismatched with the sender. But the engine is about right do you think?