v8 coolant system

[wooly350i]

Hi all,Can anyone throw some light on the use of a small coolant pipe connection on top of the v8 lump front nearside, at present mine is connected via silicone to one of the bottom header tank connections, I'm asking coz a mate reckons its connected wrongly to the tank, he thinks it just needs to be plugged off. Reason I'm in doubt is because the original temp gauge in the car does funny things when driving ,ie, suddenly starts to rocket up to 100 and even 120 degrees before falling back quickly to a reasonable 80 degrees and less Luke there is an air lock causing it.
As it is connected to the header tank along with two other pipes I'm thinking there could be flow through that pipe and dragging air in from the top of the tank, the engine is fairly modified but the cooling should be he same hopefully, thoughts welcome please.
Had a good blat out in the old git yesterday evening and the motorway cruising was fine, the temp gauge issue occurs when slowed own or in traffic, next week Im booked in on a set up session at Surrey rolling road so it would be good to get some views. Cheers for now,wooly.

Edited by wooly350i on Thursday 17th April 09:35

[mrzigazaga]

Hi Mate..Sometimes the water temperature will do that as the thermostat hasn't opened yet...When it does the temp drops quickly...I believe that the pipe shown normally goes to the water jacket under the front L/H side of the plenum...Mine is capped off...Unless i move to siberia...

PS: As regards to the water temp...It should only do that from cold...If it is happening in traffic then what is your fan set up...Do you have an alloy rad with twin fans?..Are they calibrated to the correct temperature?...

Edited by mrzigazaga on Thursday 17th April 09:40

[wooly350i]

Morning Mark, I think you are correct about water jacket on plenum but mines been disconnected for a long time now, just unsure what to do with the block connection now, the temp rise us alarming although I don't think its a major problem as things seem to run fine and it doesn't blow water out the overflow.

[mrzigazaga]

As i understand it the connection in question helps to warm the air inside the plenum on really cold mornings...However cold air also gives better performance..Mine has a bolt inside and a clip to blank it off..
If you have a fan stat fitted then i would set it a degree or two over what the thermostat is that you have fitted in the car, i:e if you have an 88 degree then set it to just over 90...It would be wise to check the temp in the tank with a probe thermometer and the rad and pipes with a laser pointer thermometer...Ziga

[wooly350i]

So if one outlet from plenum jacket went to the block connection where did or does the other plenum pipe go to?

[mrzigazaga]

Sorry mate...Not sure..I have been looking and did look a while back when i noticed mine was capped off...Cant find any info at the mo...

[wooly350i]

Can anyone else help with original plumbing layout especially around plenum water jacket pipe routes,?wooly

[jon haines]

On my 350 there is a hose from the expansion tank to the underside of the plenum and another hose from the underside of the plenum going to the engine. I think this is how the factory did it but that is different from the rover and range rover cos what did they know?

[wooly350i]

Thanks Jon, I was thinking that's how it was but wasn't sure, hence reason why my pipe goes from top of block straight to tank and cutting out the plenum. I may try just blocking it off with a manual vent and see if thermostat in car behaves differently.

[Wedg1e]

Aye, on mine I think that hose from the top of the inlet manifold fed the throttle body heater, the flow from which was then tapped into a line feeding the header tank.
I got rid of the throttle body heater and linked the two pipes, not noticed anything different (as in, it still loses coolant in a random fashion ).

[wooly350i]

I'm just wondering as the pipe goes straight back to the tank now there is obviously flow through it via the tank and maybe the pressurised air at the top of tank is getting pushed back down the pipe to top of block where it then creates intermittent air collections thus I get this occasional high reading on the temp gauge before it then quickly falls back after say 10 seconds give or take, its like flying an old Lancaster bomber having to watch the gauges all the time, makes you feel alive
I'm gonna block it off sometime over weekend and experiment.

[mrzigazaga]

As i said mate, Mine is capped off and i don't experience any issues...Other than only having a manual override for the fan and forget sometimes to turn it on until its in the red...
It would be interesting to know what fan set up you have as i still think that if you have a separate fan control..(Like Delilah) then it could be set to come on at a slightly lower temperature.

[Tasmindevil]

On LR V8's the top connection (as stated previously) goes to the plenum to warm the air in very cold climates to aid running then from there it returns to the header tank, not really necessary for the cilmate we live in. My previous wedge had this set up with the output from the plenum into the radiator header tank plus I have seen the output on other wedges go into the top hose pipe, my current wedge takes the inlet manifold pipe straight to the header. It can be blanked off but I suggest it goes to the header as being the upper most point of the engine it is ideal for bleeding any air out of the system when filling and will not effect the systems performance. As for temp rises it you are happy about the thermostats operation then focus on the fans, depending on the thermo switches type/location check that its clean, rust, muck, sedement or any coating will insulate the switch from operating at its right temp.

[wooly350i]

Kenlowe fans and their control pack which includes two relays,fuses and switch temp adjustment screw plus I've got the over ride switch too, all of which are independent from the original temp sender unit and gauge, talking of high points on the block I'm assuming the air would be able to shoot up the main thermostat housing to the silicone/rubber elbow and with a bit of force to the swan neck cap/vent.
If plugging the connection works I suppose the alternative option to prevent backflow from the tank would be to pop a non return valve on that line so at least air would travel towards the tank.
Off to work now, so laters

[The Hatter]

On the SD1 the plenum heater is fed from the connection next the the coolant temperature sensor (as TVR in the pic above) but the outlet pipe goes to the heater return pipe as it emerges from under the intake manifold. TVR chose to connect the plenum heater outlet to the (Ford...) expansion tank and then put a vent pipe on the heater return connection (this vent pipe Tees into the swan neck vent too).

I now have my car set up with the SD1 plumbing as above; plus a two connection (Mercedes) expansion tank with the main pipe off the bottom of the expansion tank connected to a large Tee piece in the bottom radiator hose.


I also get the thing where on initial warm up my temp gauge shoots into the red for a few seconds when the thermostat opens; I guess that's the hot water from the heads going past the temp gauge sender. It settles down after a few (maybe 10) seconds. I found this only happens with an 88Deg thermostat, I still see the effect with a 82Deg stat but it doesn't go into the red. I suspect this is why TVR specified a 82Deg stat - however I've found my engine is generally happier with the 88Deg stat (more consistent fueling I think, plus the heater is much more effective).

[wooly350i]

Thanks for the input everyone, useful bit of info there as well martin,cheers. Wooly.

[jmorgan]

Messing around with my caps this afternoon and that pipe goes to a tee in my pipe that feed the bottom on the header. That is the pipe that goes from the main water tank to the top of the rad.

[Wedg1e]

I have no doubt the idea is that that tapping takes any air from the highest point in the engine, sadly TVR's location of the header tank below that point means that trapped air would have to travel downhill to the bottom of the tank, something it would rather not do.

Maybe disconnnecting it from the T-piece, holding it high to let the water displace any air up it then reconnecting it might work?


Maybe what's needed is an auto air bleed as fitted to combi boilers: it lets air through to atmosphere but not water.