Whoa! Coolant on the hood?!? What's going on?

I noticed recently that I have a coolant leak in a used car that I got a few months ago. I’ve been driving this thing pretty regularly at this point, but I haven’t noticed any overheating. The engine temp stays shy of the midpoint line on the meter, both at speed and in idle.

The coolant reservoir was empty a little over a month ago, so I filled it up. A few days ago, I took a look at it, and it was empty again. Uh oh. I refit a hose that was a little loose and decided I’d just wait and see what happened after driving it some. Over the past few days, I’ve noticed slight decreases in the coolant level each day. Today was no different, except that after I drove for about 15 minutes on probably the hottest day of the year so far (about 95 degrees, don’t know if that matters at all), I noticed there was coolant sprayed on the hood. I opened the hood and there was quite a bit of coolant pooled on the far left of the radiator top, right between the coolant reservoir and the radiator pressure cap. What’s going on here?

You don’t mention year, make ,model, and mileage of this mystery vehicle, and if it has a radiator pressure cap, the pressure cap might be weak allowing coolant to be pushed past the pressure cap.

Try replacing the radiator pressure cap.


One of the hoses could have a pinhole

If the radiator’s plastic and aluminum, one of the sidetanks could be leaking

I agree. You’ve just got a leak somewhere or the cap is faulty. Likely suspects are the hoses or the radiator itself where the tanks are crimped on the radiator or the plastic tanks give out eventually. You can either try to spot where the leak is to see or you can have a pressure test done to pin point where the leak is.

A cooling system pressure test will quickly show where the leak(s) are located. I suspect more than one.

Yeah, realized I forgot make and model just after I posted. OP is now edited. It’s a 1990 Mazda MX-5 Miata. Does the location of the spill give any solid indication of where exactly the leak could be?

I’m thinking it’s a leak in the hose that I adjusted the other day. It’s old - maybe it was already leaking and messing with it made the hole bigger.

Clean up the spill and when its hot you should be able to see it seeping out if you inspect it closely enough. Hoses and radiator tanks are prime.

Older Miatas frequently have problems with the plastic ends of the radiator. Do they look kind of green? If so, that’s a good sign of aging. That doesn’t mean it’s not a loose or leaking hose, but another thing to look at on a car that old.

Thanks guys.


Yeah the radiator looks pretty greenish. I looked under the hood while running the car and quickly noticed coolant oozing from a pretty bad leak in the top part of the radiator. A guy at Advanced said there’s no hope for it, but my neighbor who’s worked on cars nearly all his life is convinced it can be patched up with some JB Weld.

Any tips?

Forget the JB weld, get a new radiator. Look on Rockauto.com, they shouldn’t be that expensive. You need to fix this soon, if it lets go you be stranded (at best) with a ruined engine (at worst).

On the hood? Why use gangsta language?

With today’s radiators, if you have a visible leak that large, replace the unit.


You don’t have any more time

You may ruin your car while waiting for a radiator to arrive

Call up one of those local mom and pop radiator shops and ask if they have your radiator in stock.

They have radiators in stock for most of the common cars
Their prices are always far cheaper than any of the big box auto parts stores

Yikes. Okay, I’ll try replacing it. Besides the threat of my engine overheating - which, as i wrote in the OP, hasn’t even come close to happening - what terrible things am I doing to my car by not getting a replacement?

If your radiator is leaking, it can ‘let go’ (one of the tanks give way) without any warning. Then you’re cooked, so to speak.

To go along with texases comment about a tank letting go, this happened with my youngest son’s car once while he was a college student and on the way home during a holiday.

The plastic tank suddenly cracked open due to overheating from a broken off airdam) and the resulting near foot long split puked all of the engine coolant out in seconds.

Well, you guys called it. On the way to get a new radiator, my car started running hot. Had to pull off and suddenly getting the repair done is much more complicated.

I got the radiator and thermostat replaced for a little over $300, and my car is running fine now. Thanks for the advice and suggestions, everyone!

You could patch it JB Weld and it might work, but at this stage, another leak will soon pop up. Most likely the leak is in the rubber gasket between the aluminum core and plastic tank and JB Weld will not fix that. Save yourself a lot of headaches and get a new radiator. Do NOT get an all metal (brass/copper) radiator as a replacement, it can cause damage to the aluminum head. Stick with the plastic tanks and aluminum core type of radiator.