Engine Running without thermostat
Engine Running without thermostat
(OP)
Hi all,
If somebody running an 4 stroke engine without thermostat, will it harmeful to the engine.
KMP
If somebody running an 4 stroke engine without thermostat, will it harmeful to the engine.
KMP





RE: Engine Running without thermostat
Regards
Pat
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RE: Engine Running without thermostat
Thanks for your reply. Could you please elaborate on this, how it will be harmful to the engine.
KMP
RE: Engine Running without thermostat
- Steve
RE: Engine Running without thermostat
You can limp home without the thermostat, but not with one that doesn't open...
RE: Engine Running without thermostat
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.
RE: Engine Running without thermostat
Regards
Pat
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RE: Engine Running without thermostat
RE: Engine Running without thermostat
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
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RE: Engine Running without thermostat
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...
RE: Engine Running without thermostat
RE: Engine Running without thermostat
RE: Engine Running without thermostat
Regards
Pat
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RE: Engine Running without thermostat
Drivers like engines to run cool. Engines prefer to be hot.
RE: Engine Running without thermostat
RE: Engine Running without thermostat
How does the water short circuit without the thermostat.
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
RE: Engine Running without thermostat
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.
RE: Engine Running without thermostat
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: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
RE: Engine Running without thermostat
RE: Engine Running without thermostat
RE: Engine Running without thermostat
- Steve
RE: Engine Running without thermostat
Realize too, a particular component could have a known high failure rate but for a tech working in the trade that could still amount to only one exposure to it in a given technicians career. So to that technician, the appearance is that it is not a common failure.
RE: Engine Running without thermostat
RE: Engine Running without thermostat
why ?
RE: Engine Running without thermostat
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Engine Running without thermostat
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
RE: Engine Running without thermostat
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Engine Running without thermostat
That was the implication in my last phrase of my last post.
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
RE: Engine Running without thermostat
Why do you have "See FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers" in each of your replies? Is there something wrong here with the postings?
RE: Engine Running without thermostat
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
RE: Engine Running without thermostat
RE: Engine Running without thermostat
You all saw the 0.9bar or whatever psi on the cap of the expansion vessel or the rad.
There is more than that.
The thermostat, even being 100% open at normal working temp still acts as restrictor.
At high RPM, pressure will build up inside the engine because the pump flow pushes against the thermostat.
I measured about 2bar while the rad cap is rated 0.9bar.
This helps in avoiding steam pockets forming around hot spots eg. between spark plug and exhaust valve seat.
You take a risk when removing the thermostat.
RE: Engine Running without thermostat