Technical Seicento - Boiling Coolant

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Technical Seicento - Boiling Coolant

barrymckenzie73

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Hi,

I've been taking a look at my Sisters 900cc Seicento which has started boiling over out of the expansion tank cap.

This had happened once or twice before she got it to me. She had bought it a few months earlier and had no problems in those months.

Initial investigation: Car idling, hot water flows around heater ( smaller diameter ) hoses as expected, oberved by feeling the hoses. Eventually Thermostat opens and Top Rad hose gets hot. Radiator starts to get hot at the top. Before bottom rad hose gets hot ( 3 mins ) the car boils up.

I assumed the problem to be either

1) The water pump not pumping the water around quickly enough as it seems to take a long time for the hot water entering at the top of the rad to reach the bottom. I took the side cover off the water pump and confirmed the impellor was still on the pump shaft and that it was secure and turned when the engine did. I did think the impellor did look tiny though compared to other cars.


2) Blocked radiator. I found the radiator had a small leak, so assumed the problem was caused by that. Had the rad recored, bled the system and the problem still exists.

However, its fine if you have the heater on blowing hot.

PLease dont ask if I bled the system, yes I did, both bleed nipples open.

Having read the forums, the additional causes could be:

3) Expansion tank cap not holding pressure: I will buy a new cap tomorrow, however to me, the system appears to be pressurised as the hoses are very firm when hot compared to when cold.

4) Fan: Works when shorted and spins freely.

5) Fan Switch: Tested in a pan of water on heat, it opens / closes around 90 degrees.

4) Thermostat: I have felt the top rad hose go from cold to hot indicating that the thermostat has opened.

To me its as if the water pump is not circulating the water quickly enough, how can this be ?

Two more things :-

a) WHen filling the system with water, it appears that the water takes a long time to fill the systems. i.e you top it up, the level drops, you add some more, it drops again. Eventually the systems fills up. Its as if there is a blockage in the block... can this happen ?

b) There apears to be air bubbles in the coolant, I have felt them when squeezing the heater hoses -> Headgasket ? although no water in the oil and no oil in the water.


Is the water pump impellor meant to be so tiny ?
Could the thermostat be slow, I thought they failed simple open or closed ?
Can the block get clogged ?


Help....


I could only assume the failed internally ( Impeller spiining on shaft or fell off completely ) However
 
I had a thermostat that sometimes opened and sometimes didn't and I had coolant boiling over and a temperature of 120degrees celsius, so try a new thermostat, is only about £15 at most.

Yes the system can get blocked, try flushing it out with a hose and then running some flush fluid through to finish the job.
 
barrymckenzie73 said:
Hi,

Initial investigation: Car idling, hot water flows around heater ( smaller diameter ) hoses as expected, oberved by feeling the hoses. Eventually Thermostat opens and Top Rad hose gets hot. Radiator starts to get hot at the top. Before bottom rad hose gets hot ( 3 mins ) the car boils up.

If the heater with its small pipes is working, the water pump is probably fine.

I think you have a blocked radiator. Rust is blocking many of the narrow tubes.

Take the radiator off, and flush with a hose, forwards and backwards, shake it etc.
 
Does the engine run cooler when reved. The smaller water pump on the 899 can cause a heat build up at idle, but a blip of the throttle sorts things out.

The bubbles in the water would be big if it was headgasket

Cheers

D
 
Must say my sporting is doin the same!
Went out today and bout a new header tank cap as i thought mine had lost pressure, so will give that a whirl for abit, if not theni dunno what :(
 
Just to finish this thread off.

I Believe the problem has now been solved, I week 2 days later and no reoccurence with daily driving and on longish journey completed.

Solution :- New Thermostat.

Although the old thermostat was working, it would appear that the new one opens much sooner hence allowing the pitiful excuse for a water pump to circulate the water through the radiator before it reaches boiling point.

I added a new coolant expansion bottle cap was for completeness.

When I initially looked at this problem I did remove the original thermostat and give it a few presses to make sure it wasn't siezed. The car worked fine for a couple of days after that before acting up again. I'm guessing the "exercising" of the thermostat give it the ability to work normally for a limited period of time.

I hope this is the end of the story. If the problem reoccurs I'll post again detailing how I set fire to the car and claimed the insurance
 
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