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Coolant Bypass


garrycol

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My old 3.5 had a dedicated coolant bypass on the back of the water pump so that when the thermostat was closed the water pump did have to work against a closed system and a small amount of coolant would still circulate.  As well there was a small pipe that connected the inlet manifold to the upper tank of the radiator.

That engine is now gone and I have fitted a Thor 4.6 to the vehicle but as the convoluted cow bladder type thermostat does not fit my arrangement I have fitted one of Nige's thermostat housing mods that makes the Thor similar to the older V8s thermostat housing.

However as the 4.6 water pump is used there is no bypass function which I assume was in the cow bladder arrangement.  Next to the coolant temp sensor in the Thor manifold there is a small coolant outlet just to the right of Nige's coolant sensor - Nige's heater outlet is to the left.  See pic.

First question - what was this small outlet used for in the original Thor system.

Second question - can I just connect the old hose I have from the header tank of the radiator to this outlet and provide a small bypass for the water pump when the thermostat is closed and I have the heater turned off.

 

Thanks

 

Garry

 

 

Bypass.jpg

Edited by garrycol
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My old 4.6 was plumbed to use the heater as the bypass circuit.

From memory it used the bigger of the two pipes in your picture around the left and then behind the engine to feed the heater. The return ran back to a dedicated feed on the main radiator.

(Assumes what we see is the front of the engine and the top of the thermostat housing)

The smaller pipe ran to the header / expansion tank and effectively gave a way to bleed air out of the plenum arrangement. 

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Thanks I assume you are talking about something like a P38 where hot coolant runs through the heater all the time - my system is different and has an old style heater with a valve that opens and closes manually so coolant from the large pipe only flows when the heater is on and generally it is off so no coolant bypass when the heater is off.

Cheers

 

garry

 

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Apart from the octopus thermostat housing, that's pretty much how I had the 110 plumbed in.

Thermostat was in the top of the plenum and piped direct to the radiator.

Heater return went into the top of the radiator.

Throttle housing I plumbed out and took the feed direct to the expansion tank.

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Thanks for the diagram - in my system I do not have any of the green pipes, the purple pipe or the overflow bottle  or the hot water pipe from the top radiator hose to the thermostat - indeed I don't have that thermostat as mine is effectively in the top radiator hose (thermostat housing) like all older RV8s .  What I do have is a heater tap in the hot water pipe going to the heater matrix so when it is turned off there is no bypass.  So I am going to run the brown hose (item 3 in the diagram) to the radiator rather than the throttle body as I will not have much chance of it freezing up.

 

garry

Edited by garrycol
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I was thinking back after seeing this diagram Garry....

I had issues with my RV8 when my heater matrix was blocked.... (Not that I knew that was the cause initially)

My engine used to heat up from cold, get a tad too warm too quickly and then the thermostat would open. This would result in loads of flow and the cool water from the radiator  would effectively mostly close the thermostat again causing another hot flash in the top of the engine.

I tried drilling holes in the top of the stats to various sizes, running with restriction plates instead of thermostat etc. to calm these peaks of heat.

When I thought it through, it pointed to not enough water in the bypass loop.... So I changed the heater matrix, went back to a standard 88 degree thermostat and all my troubles were gone.

Remembering this, I'd be worried that you too wouldn't have enough water flowing through the plenum to allow the engine to warm up more slowly and you may get the hot spikes like I used to.... 

Heat is not a friend of RV8's....

 

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Yes I hear what you say hence why I put up the thread.  I will go with the approach I intend but if I have the issues mentioned I will put in a direct bypass from the heater pipe outlet in the inlet manifold to the lower radiator hose.

Cheers

Garry

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It'll be pretty obvious Garry.... If it heats up real fast and then when thermostat opens it cools off noticeably on the temp gauge then you will need the heater circuit. 

Is it a stock temperature gauge with a 50 degree fudge factor to keep it nice and central on the dial or something more accurate to help you keep an eye on things?

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I have an aftermarket temp gauge so reads as it should.

I also have a secondary system with a sensor on the block that measures the temperature of the metal of the block - it is interesting to compare the two - the metal temp stays quite stable but the coolant temp rises and falls with the movement of the thermostat - showing that the cooling system does its job by changing the flow of coolant around the engine as demand changes and this results in a stable temp within the engine. This secondary system also has a sensor in the top radiator hose that sets off an alarm if coolant gets low.

Edited by garrycol
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