Coolant pressure inside engine 1

[jcd06]

It begun when a friend started talking about replacing the stock water pump by an electrical aftermarket pump on his CA18DET engine.

One of the elements in the manufacturers installation guidelines struck me: remove the thermostat.

This brought me to think about what happens inside this liquid system.

In the case of this engine, and I think for most production car engines, the path of the cooling circuit is: pump – engine block – cylinder head – thermostat – radiator – pump.
The thermostat is open when the engine is at normal working temperature.
How much its valve is lifted from its seat depends on the design and the momentary situation. Obviously this will be different at idle or when racing, when freezing outside or in hot weather.
I gathered some figures from a couple of random service manuals and I found values of 8-12mm when heating it in a pot of water.
It is not hard to imagine that the thermostat being open only that little will cause a flow restriction in the coolant path.

Many literature mention the pressure generated inside the engine and the head because the pump is pushing its liquid against the restriction caused by the thermostat.
This pressure is supposed to be beneficial because it further rises the boiling temperature of the coolant.
Especially inside the head, where the coolant runs sometimes very close to the hot exhaust gas, only separated from it by less than a centimetre aluminium wall.
As I didn't find real-life values of this pressure, I decided to measure it myself while I already planned to measure some other engine parameters.
I took advantage of the threaded hole for the dashboard gauge temperature sender in the thermostat housing to plumb-in a pressure transducer.
Link to the graph

The signal was logged and plotted against RPM.
As you can see, pressure went well over 4 bar.
Mind you, this was at around 5°C ambient. When the weather is hot, the thermostat will open further to achieve the same coolant temperature.
When the thermostat opens further, the pressure generated by the pump will decrease.
Also, this is a fairly high-revving, high hp/cc engine.

Anyhow, this 4bar is a rather high value and I must say that it surprised me.
Installing an electric waterpump and removing the thermostat, you lose this advantage completely.

I was under the impression that nowadays some cars are OEM equipped with electric waterpumps.
Am I wrong and are these just secondary pumps for accessories circuits like heating or turbo core?
Or is the pressure that I measured not really necessary and to be considered completely as parasitic in terms of power consumption?
Or are these primary electric water pumps (if they really exist) fitted to low power engines with a much better thermal design of the internals of the cylinder head casting?
After all the CA18DET was a design from the eighties.

Also worth noticing is that the curve is not flattening off at high revs. Am I right to assume that the pump is not (yet) cavitating?

I would appreciate to know your professional opinions about this.
Thank you for sharing your knowledge.

Jean


When we all think alike, no one thinks very much. ---Walter Lippmann

 

[patprimmer]

Even in tropical Oz, I believe the longer warm up time hurts fuel economy and engine wear during that warm up time which is extended.

The tropical climate makes the warm up time relatively short compared to cold climate, but still extended compared to with the thermostat installed. I guess if the typical trip is also long the % extra time spent at lower than optimal temperatures becomes small, but still why extend it at all.

Regards
Pat
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[Lou Scannon]

Pat that's my take also.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[hydroman247]

and the higher water flow eroding the engine's innards

As above, the only negative effect of removing the thermostat is a longer warm up time.

 

[140Airpower]

Simply removing the thermostat in a system that uses one will have the deleterious effects that have been repeated here. It's a very bad idea. However, the picture is different if you substitute a thermostatically controlled electric pump. The slow warmup problem will not likely exist. However, flow in bypass and diversion circuits will probably be effected depending on the system design.
The benefit of removing the thermostat for an electric pump is the reduction in total system resistance and the power requirement for a given amount of flow. IMHO for a small engine, like the CA18DET, this is a much more interesting option than for a big SBC or LS.

 

[Tmoose]

Hi BigClive,

"Most of the cars I own are older than 10 years (one is 23)."

Do any of the 'stat-less ones have aluminum cylinder heads, and are any SAABs or Subaruooos, or use Mitsubishi 2.6 engines?

Dan T

 

[BigClive]

Moose - the 23 year old car is an Oz Ford Falcon EA which has been thermostat-less for about 10 years - it does have an aluminium head.

To explain further on my views on thermostat-less engines: Obviously I don't recommend removing the thermostat on new cars or even newish cars, or in cold areas etc. - especially if they are still under warranty. I was assuming that jcd06 (or his mate) has modified his CA18DET and was probably having overheating problems especially seeing it is a turbo engine. I think removing the thermostat does help any marginal overheating problems. If the CA etc. engine has been modified I doubt if the owner is worried too much about marginal increases in fuel economy, engine wear etc. after start-up.
I don't know for sure, but I doubt if V8 Supercars, Nascars (or just about any competition engines) use thermostats.

I think thermostats are very rare creatures north of the tropic of capricorn in Oz.

 

[Tmoose]

- It was about 20F the night before. From a full cold start The old Volvo 850 was blowing distinctly warm air in less than a mile at 30 mph, and by 1.5 miles deliciously hot air.
- 4 and 5 cylinder Volvos seem better than most at keeping headgaskets intact on aluminum headed engines way past 100 kmiles.

I suspect that their scheme of forced recirculation, with a double disk t-stat that actively controls the flow thru the bypass circuit may have something to do with both characteristics.