Car thermostat permanently on.

The thermostat on my car is bust. It jammed on the other day and the engine overheated and nearly did the head gasket in. The emergency callout guy sorted it so it stays on all the time and constantly circulates water around the engine.

He says it should be OK as long as I get the thermostat replaced as soon as I can. Now that’s the problem. I can’t see myself having the money to get it fixed for a while.

So my question is will driving the car with the thermostat on for a couple of weeks cause any problems?

The thermostat on my car is bust. It jammed OFF the other day and the engine overheated and nearly did the head gasket in. The emergency callout guy sorted it so it stays on all the time and constantly circulates water around the engine.

He says it should be OK as long as I get the thermostat replaced as soon as I can. Now that’s the problem. I can’t see myself having the money to get it fixed for a while.

So my question is will driving the car with the thermostat on for a couple of weeks cause any problems?

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I’m not sure if UK terminology is different, but in the US we talk about an engine thermostat being either OPEN or CLOSED. I assume yours was stuck closed, which will cause overheating. I don’t know of any way to get one “open” other than breaking out its center, jamming something into it, or removing it. All of those require accessing/removing the thermostat, and I wonder why a new wasn’t put in then, as all of the work to do so would have been done.

Anyway, to your question–it’s not likely to do significant harm in the short term, but it can cause problems if left that way too long. The engine will not reach operating temperature. The expected results of that are warm instead of hot air from the heater and increased fuel consumption (because the electronic control system perceives the engine as still being in warm-up mode). Some of the excess fuel can get into the oil and contaminate it.

So you won’t ruin your engine in couple of weeks, but it would be wise to do the repair as soon as you can, and to have the oil changed once it’s done.

They’re not very expensive or difficult to change. The last stat I bought for my 89 mazda was only $7.99 US and only took me 15 minutes to change, and I’m not much of a mechanic.

I’ve been wondering this for some time, and this seems an appropriate place for a hijack (of sorts):

Does the thermostat in a properly-running vehicle open and stay open once the engine heats up (until the engine is shut off and cools, obviously), or does it normally cycle open and closed during vehicle operation?

Another way of phrasing the question would be to ask if the cooling system can normally dump heat efficiently enough to bring the coolant temperature back down below the thermostat’s opening temp during operation. (requiring the thermostat to close again to keep the temperature adequately high)

Thanks for the advice.

I’ll contact a garage tomorrow if it’s not going to be that expensive.

The thermostat does not simply stay open, it cycles open and shut, constantly regulating the engine temperature. The goal is to keep the temperature at a certain point. On the one hand, engines run more efficiently as they get hotter, and on the other, they can self-destruct if they get too hot. The thermostat helps achieve rapid warm-up followed by a proper and relatively consistent operating temperature.

In most conditions, the radiator has more cooling capacity than needed. One way to look at it is that the radiator’s job is to prevent overheating, and the thermostat’s job is to prevent overcooling.

IANA mechanic but in the cars I am familiar with the cooling system won’t draw away enough heat to make the thermostat close again.

If it did close your heater wouldn’t work until it opened back up again.

It may be that some thermostats hover around a midway position, but in most cars they do indeed close enough to essentially stop flow through the radiator.

Thermostats do not affect flow through the heater core. The only effect they have on the car’s heat is that if they stick open, the heat will be warm instead of hot because the engine doesn’t reach its normal temperature.

Thanks, Gary T! Very informative, as always.

I don’t know about all cars, but you could watch the cycling of the thermostat on the Plymouth I just traded in on cold start-up. The temp gage would go up to the normal position, then drop way down when the thermostat opened and let in cold water from the radiator. Then it would go back up to normal and drop down again, but not so far because the radiator water was now warmer. The it would go back up to normal and drop down some. It would finally settle down after about 4 or 5 such cycles to the steady normal position and maintain that, which I assume was with the thermostat partly open.

I used to take my thremostat out every summer in my Beretta, it kept the engine running cool, and, since it was prone to coolant leaks, wouldn’t build pressure therefore wouldn’t leak. I just wouldn’t wouldn’t have any heat so I’d replace it in the winter.