Cooling circuit: PRRT vs Bypass mod

[Ian B]

So what are the experts thoughts on the pro's and con's of the PRRT mod vs the bypass mod ( ie the one described in September 2012 Low Flying)?

 

 

[Dany]

is bypass mod the QED type?

 

we have two cars, both k series. first one has PRRT on a +250 bhp engine and the other one the QED type on a +200 bhp engine.

 

the PRRT is much more stable, temp does not fluctuate at all. QED is good to keep the temp right, but does not prevent fluctuations.

 

hope that's help

[oldbutnotslow]

Ian I must ask as a starting point why you are considering making a change from what I assume is the "normal" cooling layout?

 

Remember the old adage " If it aint broke Dont fix it!" If there is a cooling issue then you need to address this problem specifically.

 

Having read the article it seemed logical so I ignored my own advice and carried out the circulation mod.

 

Previously there were no issues with overheating or fluid being pushed out of the expansion tank

 

Following the mod it appeared that the expansion tank became part of the flow and as such it consistently filed up with coolant. I had no idea in which part of the engine the air that had previously been in the expansion tank was now sitting which was somewhat worrying to say the least.

 

I was getting fluctuating water temperature readings. I dont have a heater and I only run my car on track so it lives between 5 and 8 1/2 k rpm.

 

The only thing that had changed was the flow layout so I put it back to the original design and all the previously described symptoms promptly disappeared.

 

I dont have experience of the PRT but I again go back to my original view that unless there is a cooling problem dont go fixing it!

 

 

 

 

 

[Paul Richards]

Ian

Bypass mod made my car much easier to fill with coolant and no problems with air locks. Temperatures and behaviour are steady as they were previously.

[Ian B]

Dany, not sure what the QED type mod is?

The bypass mod in Sept 2012 LF moves the outlet from the expansion bottle from the cool return from the radiator, into the hot flow into the block.

 

Grant, I already have the PRRT fitted, after having a lot of problems with airlocks, and it seemed to work well and keep things stable, but ISTR that was fitted just before the LF article.

More recently however I have had a some coolant loss which I think has been traced to a corroded radiator (new one on order and due to be fitted in the coming week), so whilst doing so I was wondering whether there was any benefit in changing over to the LF mod, or sticking with the PRRT (given I may need to replace some old hoses at the same time).

 

Thanks Paul. To be fair I've not had a problem filling since the PRRT (probably because the standard thermostat is removed completely), and I've had quite a bit of practice recently whilst trying to find the mysterious disappearing coolant (which appears to be weeping from the rad only when it's hot, and evaporating, so no puddles or signs of coolant elsewhere).

 

 

 

Edited by - Ian B on 17 Jun 2014 11:16:03

[revilla]

On the same lines as "oldbutnotslow" ...

 

The mostly standard cooling system on mine is rock solid, provided I do one simple thing - make sure it's had a chance to warm up properly before pushing it. Which is what you should be doing on a K Series anyway for a whole host of reasons.

 

If you push it before it's warmed right through the head gets properly hot while the radiator is still full of cold water. When the bypass flow causes the thermostat to open, cold water rushes into a hot head. Not good for thermal shock or head gasket longevity and the temperature swings up and down. If you warm it up gently until there is steady flow around the system its fine. My temperature gauge sits on 80 it idle, maybe drops a couple of degrees if I'm wafting along gently with the extra flow over the radiator, goes up a bit in traffic on a hot day - but never ventures far from the 80 mark in normal driving.

 

When I say "mostly" standard, I have drilled the thermostat to help clear air locks when filling and I think that probably helps with temperature stability too as it allows a little bit of flow through through the radiator to gently clear the cold water and let warm water circulate even before the thermostat opens. Certainly on my car, nothing more seems to be needed.

[Ian B]

Quoting revilla: 

If you push it before it's warmed right through the head gets properly hot while the radiator is still full of cold water. When the bypass flow causes the thermostat to open, cold water rushes into a hot head. Not good for thermal shock or head gasket longevity and the temperature swings up and down.

Quite agree regarding allowing to warm up before pressing on etc, although I believe that's one advantage of the PRRT, in that most of the coolant bypasses the rad with a little still going through it, so the engine warms up quicker and there isn't a cold shock when the thermostat (in the PRRT) needs to open fully and allow all the flow through the rad (although I may be wrong!).