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Running without a thermostat
Irony - 25/4/16 at 12:29 PM

My Rover V8 3.9 overheated the other day. I had installed a warning light that comes on at 95c and I pulled over immediately and turned it off. A hose had burst off. The cap on the heater matrix takeoff. I drained the system and replaced the caps. Refilled and the car is still overheating. Radiator is stone cold and the fan not kicking in. Presumed a airlock and rebled the system. Still over heating. Rebled again and still overheating. Checked the sensor and fan but they are fine. Radiator merely warm, pipes after the thermostat also just warm. Talked a mechanic neighbour (40 years running a his own garage) and we removed the Thermostat. Rebled and now all works fine. He suggest faulty bleeding or the intial overheat broke the thermostat or was caused by a broken thermostat and the resultant extra pressure blew the pipe off. He said as I don’t drive the car in the winter at all over cooling isn’t a problem so running without a thermostat might be the way forward.

I have always been concerned about under bonnet temps. When driving along the temps are rock solid about 80-85c. However as soon as you stop the fans kick in within 30secs. Running without the restriction of the thermostat might help this. i.e better coolant flow.

Should I run without a thermostat?

CosKev3 - 25/4/16 at 01:22 PM

Try it and see I would,if your happy with it leave it out.

I think there are various arguments regarding this though,as the thermostat in some cars controls the speed the coolant passes through the rad,so by removing it your coolant can pass through the rad too fast and not get cooled enough.

coozer - 25/4/16 at 01:52 PM

Try a 74° thermostat.

britishtrident - 25/4/16 at 03:58 PM

Try a drilled stat the holes can be quite small even on V8

However I am slightly concerned that the engine is already running at 80c without a stat at current cold ambient temperatures

killerferret666 - 25/4/16 at 04:09 PM

take the old thermostat.

Boil some water in a pan in the kitchen. Drop the thermostat in.

If it doesnt open, the thermostat is at fault and you should be able to just put a new one back in and run normally.

[Edited on 25/4/16 by killerferret666]

Irony - 25/4/16 at 04:16 PM

quote:
Originally posted by britishtrident
Try a drilled stat the holes can be quite small even on V8

However I am slightly concerned that the engine is already running at 80c without a stat at current cold ambient temperatures


I had a 74 degree stat and it ran about 80c. I am yet to run it without a stat on the road. I even drilled small holes in the 74c Stat.

The different stats that Land Rover made don't seem much use to be honest. They did a warm weather stat at 74c and normal stat at I think 82c. I compared both in the same pan on the stove and they both opened at the same time. Useless.

rusty nuts - 25/4/16 at 05:54 PM

Running without a thermostat can cause more problems than it solves , rapid engine wear being one and also cavitation of the coolant actually causing overheating . Classic Mini would crack the head without a stat Special Tuning used to supply a restrictor to replace the stat. As it seems to be running hot my first check would be a sniff test to check for hydrocarbons in the cooling system then make sure all the air going into the nose cone is A not restricted and B ducted so it goes through the rad . My under bonnet temperature was always a bit high Water Wetter dropped the coolant temp but opening some vents in the rear of the bonnet helped

killerferret666 - 25/4/16 at 06:23 PM

quote:
Originally posted by rusty nuts
My under bonnet temperature was always a bit high Water Wetter dropped the coolant temp but opening some vents in the rear of the bonnet helped


Good point on water wetter. I run that as well just to help control temperatures further and it dropped mine as well. It gives the water less surface tension so takes heat away from the engine more and also allows raiator to remove more heat.

think mine dropped between 10 - 15 degrees F so my radiator fans dont come on no where near as much when not moving.

[Edited on 25/4/16 by killerferret666]

Rob Allison - 27/4/16 at 07:35 AM

Never run without a thermostat. The water pump needs a restriction to pump agains to work. You just boil the engine as the water flow is lower.

Irony - 27/4/16 at 11:14 AM

quote:
Originally posted by Rob Allison
Never run without a thermostat. The water pump needs a restriction to pump agains to work. You just boil the engine as the water flow is lower.


huh?

britishtrident - 27/4/16 at 12:20 PM

quote:
Originally posted by Irony
quote:
Originally posted by Rob Allison
Never run without a thermostat. The water pump needs a restriction to pump agains to work. You just boil the engine as the water flow is lower.


huh?


Running without the restriction thermostat the pattern of flow within the block and cylinder head it reduces the by-pass flow.

Oddified - 27/4/16 at 02:52 PM

quote:
Originally posted by britishtrident
quote:
Originally posted by Irony
quote:
Originally posted by Rob Allison
Never run without a thermostat. The water pump needs a restriction to pump agains to work. You just boil the engine as the water flow is lower.


huh?


Running without the restriction thermostat the pattern of flow within the block and cylinder head it reduces the by-pass flow.


True but the bypass doesn't cool the engine so it won't make it boil easier.

Ian

r1_pete - 27/4/16 at 03:21 PM

It all depends if your cooling system relies on a thermostat which has a disc on the back to close off the bypass as it opens, not closing off the bypass would cause some coolant to flow round the bypass circuit rather than the radiator, being pumped it will take the path of least resistance.

The cooling system also relies on a thermosyphonic action, whereby as the water is heated by the engine it rises up the block / head, and as it cools in the radiator it falls, also creating flow, running without a stat and an open bypass would interfere here too.

britishtrident - 27/4/16 at 03:42 PM

Thermosyphon is a dead duck compit ared to the flow created by the pump contributes almost zero to the coolant flow in a modern system.
Car that used thermosyphon alone without a pump llike 1172cc 93e Ford Pop always had a vertical flow radiator higher than the engine.

There have been V8 engines built with reverse flow cooling to improve emmisions and fuel economy.

Rob Allison - 27/4/16 at 05:09 PM

quote:
Originally posted by Irony
quote:
Originally posted by Rob Allison
Never run without a thermostat. The water pump needs a restriction to pump agains to work. You just boil the engine as the water flow is lower.


huh?


First the pump is not made to work almost open ended its outside its pumping capacity. All sorts of strange things happen, like cavitation.
also with the restricted path of the thermostst gone the coolant can take the easy route. This depands on the design of the coolant system. But basically the rear cylinders can become starved of coolant flow and overhead. The front cylinders can be overcooled.

Julian B - 27/4/16 at 07:25 PM

This is a problem I have never really fixed with my rush v8 .....so far perhaps

I ran without a thermostat on a run to Rome and whilst it was ok in the hot it was terrible over the Alps in the cold You will end up with gloopy oil and a tractor of a car

I now have the biggest electric fan I could buy plus a chainsaw pop off valve on the top hose to let me see that the system is full to the top without air locks
I also have a 4mm hole in the stat to enable a small ammount of bypass flow and I also have a ducted nosecone

With all of these measures it seems to hold its own .....just. .......I sat in traffic the other warm day for 15 mins and it survived. 29mins however might have proved too much
.I don't think there is a golden arrow on this one ...it's just a culmination of modifications that fix the problem


Good luck. Please keep us posted as I'm sure we are in for a nice warm kit car friendly summer

Irony - 28/4/16 at 08:54 AM

Read everyones comments and thanks for the input.

A lot of people commented on the fact that without a restriction the water will flow through the easiest route. I.e down some sort of bypass. I think this depends on the design of the system. I have a Rover V8 with a Edlebrock header and a custom designed cooling system. All very different from the original RV8 design. The system has a bypass but all it literally bypasses is the thermostat. So a small amount of water flows around the closed thermostat. Removing the thermostat will just allow more water to flow. However predicting cavitation (isn't that bubbles forming on the blade tips) is virtually impossible.

I am going to buy a new 74c degree thermostat and see what happens.