The Right Way To Coolant. 2005 Toyota Camry

Hi folks. I could use some help, please. All advice welcome.

2005 Toyota Camry, 122k miles, four cylinder engine.

On paper, my father owns my car. I’m making payments to him. He’s a control freak in general, but he’s always been good with cars. It’s no fun to fight with him when he’s wrong and in this case, he may be. He insists on tackling my (possible) coolant issue in a way that might be better suited to a 1969 Caprice.

Recently, I noticed that my engine was running hot. It turned out that my car was low on coolant. Once my father put more in, the engine temperature returned to normal and has remained there ever since.

However, now, my father checks the coolant about once per week. He opens the radiator cap while the engine is cold. If he can’t see any coolant (and usually he can’t), he adds some, always in the radiator, never in the overflow tank. He does this by pouring in a small amount of one-size-fits-all, undiluted Prestone and then pouring in approximately the same amount of tap water. He repeats this process until the level rises almost to the cap, then he’s satisfied. The overflow tank is at or near the full mark. It might even be a little over. I need to clean the thing so I can read the level properly.

I’ve been reading up on this as best I can and I think I’m seeing a bunch of problems.

  1. In a car with an overflow tank (which mine definitely has), you’re supposed to check the level there, not in the radiator. Yes? Google says my father’s method was standard back in the olden days. However, while the overflow-check may be more convenient or more safe, that doesn’t mean that it’s necessarily more accurate. No?

  2. My owner’s manual insists that my car needs Toyota coolant, not Prestone or any other aftermarket brand. Of course, manufacturers always say you should use their products. After all, they want more of your money, right? Over the years, I’ve used plenty of after-market parts. But a specification is a specification and I don’t know much about coolant, so I googled. I found a post in a Prius forum where a guy who really seemed to know what he was talking about stated “The bottom line is that there is no after market coolant sold in the USA that is of the same formulation type that Toyota (or any Japanese maker) uses. Get thee to a dealer for the stuff.” You can read the post here: . You’ll have to scroll about halfway down the page to find the post in question.

  3. If I’m using the wrong kind of coolant, what sort of problems might that cause?

  4. Tap water is bad, isn’t it? Shouldn’t we be using distilled water?

  5. If my father is right and the car does need to have coolant added all the time, doesn’t that mean I have a leak or some other problem? Shouldn’t we be looking for the cause?

  6. What happens if he overfills the coolant system? Does the fact that nothing bad has happened yet indicate that he’s right, that the car does need more coolant on a regular basis?

If I have to take this thing to a mechanic, it’s going to be a fight. So before I commit myself to it, I’d like to know as much as possible. Thanks.


I have no problem if he is using a universal coolant. If there is coolant needed in the radiator and not the overflow that is a sign the overflow is not working properly to me. I do not think overfilling is a possibility, as worse case scenario it flows out the top of the jug if operational. Might try a new radiator cap. my 2 cents


Replace the radiator cap.

If the radiator cap is weak coolant can escape from the radiator as a vapor.

And if the radiator cap is weak, it won’t allow the coolant to go from the reservoir to the radiator when the radiator gets low on coolant.


I would never had thought to check the radiator cap. Thanks.

“And if the radiator cap is weak, it won’t allow the coolant to go from the reservoir to the radiator when the radiator gets low on coolant.”

Because, by permitting the escape of air/gasses, it alters the pressure in the system? And the pressure affects how much fluid flows from point A to point B?

When I have to talk to my father about this issue, it’s going to help if I know the whys and wherefores.

You’re fast learner. :smile:


To check the coolant level in the radiator with an overflow bottle it is necessary to remove the radiator cap to inspect. A faulty radiator cap can result in the reservoir being over full while the radiator is dangerously low.

Green Prestone should not be mixed with the red or purple coolants in most new cars. As mentioned already the universal coolant sold by Prestone and others is acceptable but I personally don’t like to see a radiator full of a soup of unknown origin.

Your father’s intentions are commendable @Clay. With many things it is worthwhile to be overly cautious and automobiles are near the top of the list and I would suggest getting a small inspection mirror and flashlight to look behind the water pump pulley for indications that the pump is seeping. There is a weep hole that will show a telltale discoloration when coolant escapes at high temperature. If you do some searching on this forum you will find many motorists with catastrophic engine damage due to overheating that could have easily been avoided. A $1,500 to $2,500 repair might put a crimp in your style.

As far as I can tell, the coolant colors have not been mixed. I’ll double check to make sure, but I think the coolant in the car is redish and so is the coolant coming out of the bottle (I’m positive that neither is green). I should have mentioned that in my initial post.

And now that you mention it, I recall that my father did check out the water pump. He had me google to find out where it was. (I found him a Youtube video. He sort of knows how to use Youtube. Google, not so much.) He didn’t find anything amiss, but I can quiz him on the specifics.

I can replace the radiator cap for less than fifteen bucks, so I don’t see any reason not to give it a try. But I’m curious… is there a more directway to determine whether gases are escaping?


You use a radiator pressure cap tester.

The radiator cap has a pressure rating. It’s usually between 13-16 PSI.

You connect the radiator cap to the tester, and pump pressure onto the radiator cap to see at what pressure it opens up at.


You have been given good advice so far. Another potential problem is that your engine is prone to stripped head bolts, just google it for generation 5 Camry’s. If this is the case your problem could get worse fast. You have to check behind the engine, where the intake manifold is, under it there is a piece of foam, make sure it is dry. If you see traces of coolant there, you are in trouble.

Coolant needs to be topped off every several months, not once a week. Replace the radiator cap, if the system still goes low in a week have the system pressure tested and checked for leaks.

The Prestone universal coolant probably won’t hurt anything at all, but as was pointed out above many people don’t like mixing coolants. I don’t use the universal coolants in anything. To the best of my knowledge the difference in price is only a few dollars a gallon.

Thanks, folks, for all the help. If anyone has additional advice, I certainly won’t turn it down. But for now, I’m going to try replacing the radiator cap.

Regarding the radiator pressure cap tester… I don’t suppose it would make much sense to spend a couple hundred bucks on a tool that will tell me whether I need a ten dollar radiator cap. However, that information will come in handy when I talk to my father about it and, if I end up taking the car to a professional repair shop at some point, I can ask them whether they have such a gizmo.

Agan, thanks.


You are right that it is simpler to just replace the radiator cap. It’s about $15 and takes about 15 seconds, you can do that by yourself.

Your dad is right to check the radiator the way he does. I the system is working properly, the radiator will always be full and when cold, the level in the reservoir will fall. If the reservoir level is not falling but the radiator is not full, then you have a problem somewhere.

One more thing to check, some reservoirs have a tube in the cap that goes down into the tank. The overflow hose on these types goes to the top of the cap. If yours has the overflow hose going to the top of the reservoir cap, check for the hose on the inside. If it doesn’t reach down into the coolant, the system wont work properly.

Also check the overflow hose for cracks or looseness. If it is cracked or loose on either end, replace it, it too is cheap.

All the above advice is excellent. Yes, just replace the radiator cap, might well solve the problem. It is necessary when there’s a question about the cooling system to check the coolant level in both places, the overfill bottle, and the radiator itself, so your dad is right about that. And no harm done, double checking at both places is just being prudent.

As something to compare to, on my early 90’s Corolla I have to add about a cup of coolant per year to keep it topped off. If you and your dad are finding you need to add at a considerably higher rate than that, something is definitely amiss. If you don’t see any visual signs of leaking, like from the water pump weep hole, around the thermostat gasket, ask a shop to pressure test the cooling system. If there’s a leak somewhere, this test will show indeed there is one. It won’t necessary spot where it is, but the shop will have other methods to discover where it is leaking.

Yes, most of the experts here say it is best to use Honda Toyota coolant and distilled (not tap) water. But in my 20+ year old Corolla I’ve only used standard Prestone and tap water and the only the normal cooling system problem you’d expect in that old of a car, needed a replacement radiator one time, and a replacement thermostat another time.

Until this is all resolved, make sure to check the dash coolant temp gauge frequently. If it shows signs of overheating, one thing you can do is turn on the heater to full “hot” , and the heater fan to full blast. That will supply some add’l engine cooling.

“Yes, most of the experts here say it is best to use Honda coolant”

Not me

Sine OP is talking about a Camry, I won’t be saying it’s best to use Honda coolant

I say it’s best for OP to use Toyota coolant


@Clay201 wrote:

All advice welcome.

When I read your opening post, my first reaction was if my father was still alive, I would welcome and cherish anything he wanted to do helping me with my car.

Prestone makes a 50/50 mix for “Asian” cars. Buy some and have dad use it for topping off the coolant. You need to find the root cause of the coolant loss. Maybe a minor thing, like a small leak a loose clamp or bad cap. I just suspect you might have a blown head gasket. A full over flow tank and still adding fluid at the radiator caps means air or exhaust gases are getting into the coolant. Once you have the real problem fixed then get the old coolant flushed out and get it refilled with fresh stuff.

Yep, just stop at the Toyota dealer and pick up an new OEM cap and a gallon of antifreeze of the proper type. That should end the argument.

In the old days there was no container to collect the antifreeze so when the coolant heated up and expanded, it was just pushed on the ground and there would always be lowered level in the radiator when checked cold. The purpose of the tank was to keep the radiator full and also not dump it on the ground. So when the coolant heats up it gets pushed into the tank. when the coolant cools down, it is pulled back into the radiator to keep it topped off. If it is not being pulled back into the radiator, you have air coming in somewhere-either back cap, leaky line, leaky tank, etc.

Adding to Bing’s explanation, it was around 1971 when, emission standards got tighter, that the overflow tanks became more widely used.

Prior to that time-frame, engine coolant rarely “boiled over” or “overheated” during normal operation. Engines ran cooler and thermostat temps were lower. A radiator by itself, with an air pocket near the top was sufficient.

Then 192 and 195 degree thermostats became popular. Engine ignition timing curves were retarded to help with emissions, but that caused engines to run hotter. The result was engines ran much closer to “overheating under normal operation”. (E.G. getting off the highway and immediately pulling into traffic on a hot day would cause the engine to temporarily overheat.)

The solution, as Bing explains, was to let the overheating occur by design - by having the coolant boil over into an overflow tank. Then as the engine began to cool, that coolant would be sucked back into the radiator.

My owner's manual insists that my car needs Toyota coolant,

Toyota does NOT make coolant…It’s made for them by one of the coolant manufacturers.

If you want the exact same formula…use Zerex Asian formula

“If yours has the overflow hose going to the top of the reservoir cap, check for the hose on the inside. If it doesn’t reach down into the coolant, the system wont work properly.”

Thanks for the idea. I’ve now checked it and the hose does reach down far enough.

“…Also check the overflow hose for cracks or looseness.”

When we first started checking the coolant, we did discover that the hose was coming loose. It has since been fixed with a makeshift hose clamp and we’ve been keeping an eye on it to make sure it doesn’t dislodge again.

" ask a shop to pressure test the cooling system."

Thanks for this one. If the cap doesn’t work, I think we’ll be doing this. Even if I have to fight with the old man about it, I think I can make it happen.

“Prestone makes a 50/50 mix for “Asian” cars. Buy some and have dad use it for topping off the coolant.”

This, on the other hand, I can NOT make happen. Good suggestion, though.

“just stop at the Toyota dealer and pick up an new OEM cap and a gallon of antifreeze of the proper type.”

I can’t make this happen either, unfortunately. Once the current issue is resolved, though, I might be able to get away with taking the car to a Toyota dealer.

“my first reaction was if my father was still alive, I would welcome and cherish anything he wanted to do helping me with my car.”

I wish your father were alive and helping you with your car. But you’re going to have to take my word for it that I’d be better off doing this (and everything else) on my own.