Cooling System Problem

[TorontoTim]

Guys, I need your collective wisdom, please.

 

Now that I have "cured" my previous overheating problem, I have uncovered something new - although I suspect that it's related to the original overheating...

 

After maybe an hour of fairly spirited driving and when I stop the car (but before I actually switch off) the overflow pipe from the radiator is expelling coolant into the overflow bottle. Signioficantly(?) this overflow is VERY frothy - when the bottle is only 1/2 to 2/3 full, frothy is welling out of the top.

 

Additional information:

- I have recently flushed the block, heater and radiator with a proprietry flushing agent.

- I have recently added a high-effeciency water pump

- I am confident that the radiator is good - I took it off and flushed it both ways

- I have an electric fan

- I have a 7lb rad cap - not tested for pressure, but it's fairly new

- I have removed the thermostat

- both coolant and oil aere "clean" - there seems to be no cross-contamination whatsoever

 

Any ideas as to what is causing what looks like a pressure build-up or the frothing? I've done a search, but couldn't find anything on this - have read a lot about overheating and airlocks etc., but those problems SEEM to have been eliminated here.

 

Thanks,

Tim

Edited June 5, 2009 by TorontoTim

[Smokey]

Hi Tim, I don't know whether this is part of your problem, but it may be better to fit one of the original sleeve-type thermostats to reduce the flow throught the bypass when the engine is warmed up. There are threads dealing with this, describing how racers often restrict the flow through the bypass. Re the froth, that may be the remnants of the flushing agents you used. Is the coolant level at spec when cold? On my long-neck rad, it needs to be about 1" below the cap when cold, or I get a lot of overflow when hot. Just some thoughts...

[graeme]

- I have recently added a high-effeciency water pump

 

Tim,

 

While it is possible that it is the remnants of the flushing agent, I have also heard that high performance pumps can cause cavitation which may induce frothing in the coolant.

 

Cheers

Graeme

[TorontoTim]

Thanks, both.

 

I flushed out both rad and block again with clean water and filled the system with just water to a little below the top (I have a later 4A-type radiator, btw). I've only had a chance for a couple of 45 minute runs so far - although it is a lovely warm day here in Toronto - and, so far, all seems much improved. Only an inch or so of water in the overflow bottle.

 

Based on some other posts I found on a new search, I have retightened all the unions/jubilee clips in the hope that the system will suck the overflow back in as the water cools due to the vacuum created, but so far to no avail. Also, I took the block tap right off (rather than just opening it as before) and a spoonful of serious gunk came out from there. Not enough, I think, to have caused a blockage around the cylinder 4 which might have caused a localised hot-spot, but it can't have been helping...

 

So, perhaps remnants of flushing agent combined with the extra stirring of the uprated pump was causing the problem. Either way, I certainly had (have?) some kind of issue where excess pressure seemed to be being generated in the system. Even though the temp was holding at no higher than 185 degrees, a bottle-full of coolant and froth was being pumped out...

 

I'll give the car a proper thrash tomorrow (or later in the week if the predicted rain-fest arrives) and report back. Next stop will be head off to poke around in the waterways and check gasket and liners for leakage.

 

thanks again.

 

Tim

[pampa]

Thanks, both.

 

I flushed out both rad and block again with clean water and filled the system with just water to a little below the top (I have a later 4A-type radiator, btw). I've only had a chance for a couple of 45 minute runs so far - although it is a lovely warm day here in Toronto - and, so far, all seems much improved. Only an inch or so of water in the overflow bottle.

 

Based on some other posts I found on a new search, I have retightened all the unions/jubilee clips in the hope that the system will suck the overflow back in as the water cools due to the vacuum created, but so far to no avail. Also, I took the block tap right off (rather than just opening it as before) and a spoonful of serious gunk came out from there. Not enough, I think, to have caused a blockage around the cylinder 4 which might have caused a localised hot-spot, but it can't have been helping...

 

So, perhaps remnants of flushing agent combined with the extra stirring of the uprated pump was causing the problem. Either way, I certainly had (have?) some kind of issue where excess pressure seemed to be being generated in the system. Even though the temp was holding at no higher than 185 degrees, a bottle-full of coolant and froth was being pumped out...

 

I'll give the car a proper thrash tomorrow (or later in the week if the predicted rain-fest arrives) and report back. Next stop will be head off to poke around in the waterways and check gasket and liners for leakage.

 

thanks again.

 

Tim

Tim, sounds like you have the wrong cap on the radiator.The standard type caps only allow water out the overflow. A rteturn system needs a cap with different seal and a small return valve.I had a similar problem and found my supplier had sent me the wrong cap,replaced it and all is now well. Also being a new cap is no guarantee it is any good,quite a few are duds.You should also refit the thermostat as they control flow as well as temperature. No water came outy my drain tap also removed tap to find the liner was hard up against the opening and no water can get out. Pampa.