Engine Running without thermostat 2

[kmpillai]

Hi all,
If somebody running an 4 stroke engine without thermostat, will it harmeful to the engine.

KMP

 

[patprimmer]

Yes

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[kmpillai]

Mr Patprimmer,
Thanks for your reply. Could you please elaborate on this, how it will be harmful to the engine.
KMP

 

[SomptingGuy]

It'll always be running either too hot or too cold, never optimal. More than likely too cold if it's just had a broken (stuck) thermostat removed.

- Steve

 

[Dan320]

You can limp home without the thermostat, but not with one that doesn't open...

 

[Tmoose]

When I begin to heat up a piece of steel with a torch I can see moisture condensing on the metal's surface.
If the cylinder walls are too cool then similar condensation of moisture and some nasty products of combustion occurs. The result is corrosive wear of the cylinder and piston ring, and maybe some abrasive and other types of wear as well.

I believe this is the source of the frequently heard "most engine wear occurs at start up ."

Coated piston rings (chrome, moly) have many benefits over iron faced rings, including resisting corrosive wear better.

Modern fuel injected engines make major decisions based on engine and coolant temperature. A cold engine is fed a richer mixture, and running rich with cold cylinder walls is probably not very very good for long term life.

 

[patprimmer]

Also the water may not evaporate out of the oil, thus reducing the lubricating efficiency.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[macquari]

I am no expert but was once told by someone who thought he was that engines rely on the thermostats to regulate water flow so that there is no fluctuations in temperature and water is kept in the radiator long enough to be cooled to the desired temp.Also they keep a supply to high areas of the engine if the coolant level is low If I have been mislead please correct me and disregard this information.

 

[patprimmer]

A thermostat closes and almost stops water flow until the engine warms up so that it warms up as quickly as possible.

Once warmed to the set point, the thermostat starts to open, and adjusts itself to maintain the temperature within the set range so long as the radiator has capacity to keep it cool.

Until the engine warms up, diluents in the oil (like fuel and water) are not evaporated out. Also the pistons are loose in the bore and bearing clearances are wide. The wide clearances increases impacts as the clearance takes up suddenly as pistons rock in the bore and the loads on bearings changes direction. Excessive tappet clearance can also cause cam and tappet wear. Pistons also wear as the edges of the skirts rather than the full face bear on the bore as the piston rocks excessive. This also wears a barrel shape on the rings.

If the open thermostat caused the water to flow slower, it would not effectively give the water time to cool, as the water would be hotter as it had time to pick up more heat while in the engine. To look at it another way, it passes the water though the radiator faster, but also more often.

We did this a short while ago. It should be easy to find wit the site google feature.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[JohnLear]

A little off topic, I once did an engine conversion (from BMC A series to Fiat 125 twin cam), and encountered something I've never seen before or since.

Once the 125 engine had been fitted to the recipient car, when the thermostat opened it allowed cold coolant to flow up through the motor until it reached the thermostat, at which point the thermostat would close again. This resulted in the engine temp cycling up and down several times before a stable engine temp was reached. The guage needle would reach 'normal', then plunge quite quickly to near the bottom of the dial, causing me to become concerned about the possibility of thermal shock.

The rather spooky thing is that while I was in the process of doing this conversion (and before I'd fired the motor up) it had crossed my mind that such a phenomena might be possible, and I was wondering why it never did. And then it did...

At any rate, it turned out that in the Fiat 124 Sports (more or less the same engine as the 125), the Fiat boffins had moved the thermostat from the typical location in the top of the head to a remote plastic housing located between the head and the radiator. This housing had two outlets, one to the radiator and one back to the bottom of the engine, and allowed coolant to flow through the motor without flowing through the radiator, until the thermostat opened.

Removing the stock 125 thermostat and fitting this bypass system cured the problem, but strangely, the 125 engine hadn't exhibited this behaviour when it was installed in the donor car, only when transplanted into the recipient...

 

[Silverbullet86]

without a thermostat, your engine would run cooler than it should. This may or may not be a good thing. Adapt this to your application.

 

[dcasto]

an old carburated engine in the 60's ran just fine with no thermostat. Of course, who cared about efficency then.

 

[patprimmer]

They ran fine, but they did not last as long due to longer warm up times. With lots of short trips, they may rarely reach designed operating temperature.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[curtis74]

If the engine doesn't reach operating temps, the fuel trim will be excessively rich causing increased cylinder wear, and the oil won't reach proper temps which can turn it into sludge... especially with the extra fuel being dumped into combustion.

Drivers like engines to run cool. Engines prefer to be hot.

 

[Thecardoc]

One of the biggest problems without the thermostat is that the coolant "short circuits" the engine. This results in portions of the engine that are very cool, and others that could actually be overheating.

 

[patprimmer]

Umm

How does the water short circuit without the thermostat.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[Thecardoc]

A "short circuit" does not apply to only electronics. In water treatment a "current" that allows water to flow straight through a tank and therefore reduce the contact time with a reagent such as alum for flocculation is known as a short circuit. Baffles have to be added, and sometimes moved to provide a resistance to current flow.

In an engine coolant system with no thermostat causes coolant to flow from the pump, through the front of the intake manifold, to the radiator, and then right back to the pump, often times skipping the entire rear portion of the engine. (Think conventional V-8 designs) This problem has been reduced by re-engineering engines so that coolant flow traverses the block, and leaves from the cylinder head on the opposite side, but that does not actually eliminate "hot spots", where the coolant flow is allowed to bypass a particular area. When coolant can bypass an area, it is taking a "shorter path" and is the reason for overheating. The idea that the coolant gets through the radiator too fast and causes overheating as another poster responded is incorrect.

"Normal" coolant flow has coolant circulating the block and head and picking up heat until the thermostat opens. Then you should get in effect a "figure 8" with coolant circulating the engine block, as well as the radiator. The thermostat serves as a baffle to prevent all of the coolant from only flowing through the radiator.

 

[patprimmer]

Ummm

I think as the water enters the block through a relatively big hole then passes through the deck to the head via a number of smaller holes, that ensures some needs to go to the back of the engine. I think the size of said holes in the head gasket are engineered to do exactly that.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[Thecardoc]

I would expect that you are correct to a degree, that the head gaskets are now designed with sufficient restrictions when new. However, problems like age, overheating, and then questionable repair practices in the past tended to cause situations that apparently were never fully thought through in years past. Uneven engine cooling has been one of the toughest diagnostics for field technicians to analyze accurately for a long time. The use of infrared thermometers was a major step forward for us, and even though today the occurrence is pretty well eliminated, we still have to take all of the steps to ensure an accurate diagnosis of a cooling system complaint.

 

[Lou Scannon]

Cardoc, in your experience, what is the explanation for engines that are prone to cracking failures of the cylinder heads, like for instance the Ford 2.8L V6; is it a weak design of the heads, poor coolant flow distribution in the cylinder head water jackets, a deterioration of the head gasket like you described, or some combination of the above?