5.7LX Fluctuating water temperature

Help please this is my problem and I don't see any threads that help!
Background: New engine (incl risers & manifolds) fitted 9mths ago all working, water temp solid & calorifier heating well.

Issue now:
1/ raw water cooled engine (5.7LX) comes up to temp. holds ?normal? momentarily then drops rapidly to cold, to come up to temp inside 1min, to drop back to cold ? cycle continues with oil temp increasing with running time. Calorider no longer heating. Turn engine off and turn ignition key to 1st position, water gauge registers a solid ?normal? which over time slowly drops (as it all cools).

Tried;
1/ Connected hose to raw water pump to exit overboard into bucket (filled inside 15 secs)
2/ Fitted new sender & thermostat (separately & separately tested) same fluctuating temp (as old units) perhaps with a little more range and apparent speed of cycle with new ones. Checked water temp gauge using Ohm meter (all OK ? eg working per sender resistance)
3/ Disconnected calorifier and blanked off hoses, same fluctuating water temp.
4/ With engine warm, all hoses from thermostat housing were (individually) ?flushed? into bilge with engine running. Full stream of water apparent. Also ?flushed? manifolds via drain plug into bilge, again good water flow. Re-connected calorifier hoses (individually) with same flush test. Full stream of water apparent.
5/ Took off rubber 90O elbows & exhaust ?flaps? in position (closed) did appear to open when pulled
6/ with engine warm, took out thermostat and ran engine for a few mins, steady temp very low, but more than cold, no apparent fluctuation in gauge.

Re: 5.7LX Fluctuating water temperature

Howdy and :welcome: to iboats

First I'm no expert and after seeing the term "calorifier" I had to do some digging. Found a couple of forums and a web site cow engineering which help me understand what might be going on. From what I have read it's sounding like there is air in the system. Many have put a bleed valve it the upper most point of the systems to bleed it off. There should be no sharp bends in the lines and 90 degree compression fittings count as sharp bends. Here is some of the info I have reviewed:

Calorifier thermosyphon problem - Boat Building & Maintenance - Canal World Discussion Forums

Calorifier

Sadler and Starlight Owners Association - Calorifier & Header tank

Here is a post from Vyv Cox from the last link above
With my previous system of Bukh 20, electric circulation pump and vertical calorifier I often had airlock problems at the beginning of the season. Firstly, the flow from the pump must go to the upper connection on the calorifier coil, exiting and returning to the engine from the lower connection. If the other way around the convection will kill the flow from the pump and water will not circulate. Even connected the correct way I had problems getting flow started and used to fill the system from the top of the calorifier. Once this was done everything would be OK for the rest of the season.

Re: 5.7LX Fluctuating water temperature

AllDodge, Thanks for this speedy response. I did in fact blank off the calorifier connections in my testing, and will check how they are connected this afternoon. I'm also going to check the exhaust flaps, just in case they are causing back pressure. If anyone knows how I can test the engine circulation pump whilst fitted I'd appreciate it, as I suspect this part!

Re: 5.7LX Fluctuating water temperature

UK boat user said:

AllDodge, Thanks for this speedy response. I did in fact blank off the calorifier connections in my testing, and will check how they are connected this afternoon. I'm also going to check the exhaust flaps, just in case they are causing back pressure. If anyone knows how I can test the engine circulation pump whilst fitted I'd appreciate it, as I suspect this part!

Click to expand...

If your referring to the engines water circulation pump, which I believe you are, there should not be an issue. If the engine water pump was not circulating water your engine would be overheating. From what I have read, the water pump they mention is an additional external pump used to circulate water for the calorifier. If you do not haave an external pump then getting the water to circulate is more difficult and requires every connection to be just right.

Re: 5.7LX Fluctuating water temperature

What is your engine serial number? If you have balls, I suspect the springs behind them might be faulty/broken.... With the serial number I can look up the engine and see which cooling system set-up you might have.

UK boat user said:

.... I'm also going to check the exhaust flaps, just in case they are causing back pressure. If anyone knows how I can test the engine circulation pump whilst fitted I'd appreciate it, as I suspect this part!

Click to expand...

If the flaps weren't opening, you'd be getting water in the cylinders.... The engine circ pump should have a cast brass impeller so, unlike a automotive pressed tin one, won't corrode away. The only failure mode I have seen on those pumps is the seal leaking, and water dripping out of the weep-hole...

Chris..........

Re: 5.7LX Fluctuating water temperature

Thanks, my engine is a 1995/6 motor and it does not have the "balls" in the T'stat housing. The Calorifier is NOW a red herring because I've removed all connections to the engine and blanked the plugs. When I fire up the engine it gets to temp, it then drops to almost cold, before coming back to "normal" to then drop off again.

I'm going to buy one more T'stat just in case but the hot water in a pan test was good for both.

Re: 5.7LX Fluctuating water temperature

I've had a look at the diagram of the thermostat housing and I have a few, probably obvious, questions.

The gasket between the thermostat and the housing (not the housing and the intake manifold) was replaced?
The plastic sleeve, in the right way?

That's all I can think of at the moment....

Chris.........

Re: 5.7LX Fluctuating water temperature

Sounds like a faulty thermostat

Re: 5.7LX Fluctuating water temperature

After remembering a recent thread with some similar symptoms, you may have a head gasket problem to diagnose or rule out with further testing. Good luck.

http://forums.iboats.com/mercruiser-i-o-inboard-engines-outdrives/overheating-5-7l-625168.html

Re: 5.7LX Fluctuating water temperature

thanks everyone...yes i put the plastic t'stat retainer in the correct way round. I have 2x T'stats both work in a pan (tested correctly, via hanging wire & thermometer. I have found this link on this great site...and will replace the engine circ pump at the weekend (look at the pic in this link! http://forums.iboats.com/mercruiser...l-temp-gauge-fluctuates-100-170-a-441583.html
hopefully this will be my issue solved...I'll let you all know! I'm hoping big time it's not cracked block or head, compression test OK and NO salad cream...
dom

Re: 5.7LX Fluctuating water temperature

Catastrophic water pump failures are pretty rare, but it can happen (as the pic shows). If you pull the pump and it's not physically broken, it's likely not the problem. If, after reassembly, you still have the issue, drill a 1/8" hole in the flange of the thermostat. Sometimes you can get an air bubble behind the thermostat and it won't want to function correctly. The 1/8" hole allows the air to pass through, but won't flow enough water to affect engine operating temperature. Let us know what you find..

Re: 5.7LX Fluctuating water temperature

Southtowns, thanks for the 1/8th tip. I have a new cir pump which I will fit this weekend - hopefully this will be the issue solved! However if not I'll do the 1/8th hole as I have 3x T'stats now and can afford to trash one! I'll let you know!
dom

Re: 5.7LX Fluctuating water temperature

Thanks to all contributors...the fluctuating water temperature (going to normal, and then down to almost Zero and then repeating this cycle) proved to be a broken engine circulatory pump (rare problem I accept!) and helped by this other link:
http://forums.iboats.com/mercruiser...l-temp-gauge-fluctuates-100-170-a-441583.html
where you'll see a pic of the broken vane, just like mine!

again thanks all
dom