thermostat -- any bypass in it?
Discussion
I seem to recall Steve Heath mentioning that there was a small amount of bypass in the thermostat. Can anyone confirm this? My car has leaked a load of coolant out of the rad area (either the rad itself or one of the hoses) -- it's a problem that seems to manifest itself when hot. I've topped up the water in the expansion tank (about half a pint) and am booked in at Castle TVR on Wednesday for them to have a look. But what I don't want to happen is find I've got a half-empty radiator on the way to the dealer, such that when the thermostat opens all the coolant wooshes into the empty space and I get a very big airlock.
If the rad's knackered I think I'll replace it with an uprated one.
If the rad's knackered I think I'll replace it with an uprated one.
I expect the cooling system will have a bypass (you'd have all sorts of reliability problems without one) but that's nothing to do with your problem. What you're talking about is a bleed through the stat. Most stats don't seal very well so in terms of getting large air pockets out, I wouldn't worry too much about it. Fill it as best you can, bleed the system if you know how, take a couple of bottles of water with you just in case. (If you run into trouble and the engine does start to overheat, remember not to chuck cold water straight into the hot engine. Either to let it cool down before you fill it up, or trickle the water in slowly over 10 minutes or so.)
The Cerbera water system is TOTALLY different from that of the Rover. Yes it uses liquid but that is it. 
The thermostat is located externally under thr front engine cover and is a three way design so that until the stat opens, the flow is redirected directly back to the engine. This is the bypass. When the stat starts to open, this flow is blocked off and the flow goes through the rad. Exactly what the system should do. The stat is located inside a special housing and does not use a seperate stat like the Rover V8s.
If the rad is leaking then when the stat opens, all the flow will go through it. I replaced mine with a 3 core version from Tower View. Mine had lost most of its fins and the metal coolant pipes had perforated. These also need checking. If gone, I suggest a stainless steel set from ACT. Tower View may have them as well.
>> Edited by shpub on Monday 14th June 14:16
The thermostat is located externally under thr front engine cover and is a three way design so that until the stat opens, the flow is redirected directly back to the engine. This is the bypass. When the stat starts to open, this flow is blocked off and the flow goes through the rad. Exactly what the system should do. The stat is located inside a special housing and does not use a seperate stat like the Rover V8s.
If the rad is leaking then when the stat opens, all the flow will go through it. I replaced mine with a 3 core version from Tower View. Mine had lost most of its fins and the metal coolant pipes had perforated. These also need checking. If gone, I suggest a stainless steel set from ACT. Tower View may have them as well.
>> Edited by shpub on Monday 14th June 14:16
It looks different but in fact the design of the circuit is virtually identical, the only difference being on the Cerbera the bypass is shut off when the stat opens (so you get up to 100% flow through the rad as the stat opens), on the standard RV8 the bypass is left open (so you get up to 80% ish through the rad as the stat opens). But the question being asked is not about the bypass, it's about air in the engine finding its way to the rad. The bypass has nothing to do with this, it is just a question of whether there is a bleed circuit through/round the stat while the stat is closed.
greenv8s is spot on. The rad has been leaking. The car is in the garage and is now cold, so the thermostat's shut. What I want to know is whether the water leaking out of the radiator has been replaced by that in the expansion tank. In order to do this, the water in the tank has to get past the closed thermostat. If it does, I should be OK by topping up the expansion tank. If not, I now have a full expansion tank and a half-empty radiator. Which means when the stat opens, I'll either get a rather large airlock or an empty expansion tank.
Maybe a bit of an exageration as it is similar but the actual implementation is very different as the whole pipe work etc is external. The stat is a three way unit as opposed to a two way. The bypass is a 38mm wide pipe not a small heater size version. The water pump is external and not built in the engine. The temp sensor is not in the engine either. The stat controls the flow to the top hose of the rad (IIRC)only and the bottom hose is open to the engine. If the rad looses water then it will be replaced from the engine and the expansion tank as the expansion tank feeds into the system on the engine side of the stat. If the rad is leaking water will come out irrespective of the state of the stat because it will be pressurised. Been there done that. Yes it will try to replace that from the expansion tank. Yes it is possible that air will be sucked in if the levels get low depending where the leak is.
If you are worried, why not fill from the expansion tank and then bleed the rad using the bleed screw and the ones on the two engine feed pipes.
>> Edited by shpub on Monday 14th June 16:45
If you are worried, why not fill from the expansion tank and then bleed the rad using the bleed screw and the ones on the two engine feed pipes.
>> Edited by shpub on Monday 14th June 16:45
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