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Resolved 2g Engine bay smells like coolant but no apparent leaks or burning. Any ideas?

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MattHDSM

5+ Year Contributor
113
71
Oct 20, 2018
Ottawa, ON_Canada
This is a last summer problem, but I'm just getting around to it now while the car is sitting in storage. My engine bay smells like coolant. Hot coolant. No sweet or fishy smells, just smells like if you took a jug of antifreeze and got it nice and hot.

I don't see any leaks, nothing pooling under the car. No white dried coolant stains on anything. Not losing any from the overflow either. The last time I did a cooling system pressure test, it held and I couldn't see any coolant leaking anywhere. I'm currently using a 70/30 water/antifreeze ratio w/ water wetter since I installed the FMIC. Still runs hot at 223F on a 80F day if I've been sitting in stop and go traffic, 210F driving around town, and 219F on the highway, No AC in all cases. Already working on bumper trimming, ducting, and adding an air dam. Never overheated though.

I'm using an 18psi evo 9 rad cap. 180F Motorad thermostat. Gates waterpump (3yrs old, dry weep hole). All silicone hoses, both rad hoses get hard and toasty at operating temps. Yonaka aluminum rad. Heater works great. Overflow tank is a NOS energy drink can, copying the cap/hose setup of OEM, all sealed up except for the overflow hose of course. I doubt that much stink is coming from the same tube used in the original overflow tank, but I guess it's possible.

I basically haven't got a clue as to why it smells. Do DSMs just smell like coolant? If anybody has any ideas, I'd love to hear them.
 
Last edited:
Solution
I don't think I ever updated this, but it turns out the leak was coming from in between the casting of the thermostat housing and the press fit pipe that connects the hoses to the heater core. I tried to braze the area shut with aluminum brazing rod, but the thermostat housing soaked up the heat too fast and could never get hot enough the melt the brazing rod. The solution was another thermostat housing.
If you’re smelling it, it’s leaking somewhere and no, coolant smell is not a dsm thing LOL. Drive it, let it cool and follow every coolant line. If you can’t see it, use your hand to see if it’s wet on the bottom.

Heater hoses
Fiav hoses
Turbo feed and drain
Water pump to water pipe oring
Oil filter cooler
Inspect radiator closely

If it’s a stock turbo, the rear coolant feed is hard to see unless you’re under the car. Again use your hand in the hard to see areas.

I had a very small leak at the cap (a drip here and there) and the cap was new. Ended up I needed to replace the filler neck.
 
If you’re smelling it, it’s leaking somewhere and no, coolant smell is not a dsm thing LOL. Drive it, let it cool and follow every coolant line. If you can’t see it, use your hand to see if it’s wet on the bottom.

Heater hoses
Fiav hoses
Turbo feed and drain
Water pump to water pipe oring
Oil filter cooler
Inspect radiator closely

If it’s a stock turbo, the rear coolant feed is hard to see unless you’re under the car. Again use your hand in the hard to see areas.

I had a very small leak at the cap (a drip here and there) and the cap was new. Ended up I needed to replace the filler neck.
You make a great point about being able to smell it. It's coming from somewhere, just need to track it down. I feel like it must be a slow leak coming from somewhere hot and it's evaporating before it can pool up. Otherwise I'd expect to have seen coolant dripping on the ground at least once in the past year.

You could also have a leaking FIAV gasket in the throttle body that would seep into the intake manifold.
Very well could be. I don't remember replacing that gasket when I rebuilt the throttle body forever ago. I'll check that and maybe I'll be able to see some dried coolant stains where the intake and head meet.
 
Okay, little update and I have a question now. SO I couldn't find any leaks, no wet spots, no dried coolant anywhere, not consuming any coolant either so just to be sure I bought some fluorescent dye and ran that through the cooling system. At first, again no signs of leaking, but then a few days later my water pump started slightly leaking out of the weep hole. I cleaned up the spot and took the car out for a long drive, got it nice and "hot" (210F). Checked the water pump and it was now leaking considerably more than the day before. I replaced the water pump last night so hopefully that was just a fluke with the dye and my water pump was already on its way out (had approximately 20k km on it and a winter of it sitting out in the open with no coolant in it).

What I have just noticed now that I hadn't seen before was the dye had covered the pipe that connects the heater core and FIAV hoses to the thermostat housing. I checked the hoses and they are tight, all the bolts on the housing are still torqued to spec so it doesn't seem like any of those are leaking (the green on the hose is actually a reflection from the dye). I have one theory that it is possible one of the hoses leaks out a fine mist that quickly dries due to the heat from the thermostat housing. My other idea is that the pipe looks like it is press fit into the thermostat housing, is it possible for it to be leaking? Any thoughts?

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this will solve your riddle
I thought so too, I already used one, left it for an hour at 20psi and no loss in pressure or leaks. BUT I did only use it when the engine was cold and it might be a only at operating temp leak. I'll be honest I'm starting not to care that my engine bay smells faintly of coolant. If it's "leaking" at the thermostat housing where I see the dye, and there's no discernable change in coolant level or operating temperature, I think I'm just going to leave it for the time being until I can get my hands on another thermostat housing.
 
It’s clear where it’s leaking from. Get it hot and take a close look
Yes, I agree that it is clear, but that spot is always dry. I took it out for an hour drive today to test out the new water pump (which is definitely keeping my temps lower) and took a look at that same spot afterwards and it was dry as a bone BUT it has accumulated a white powdery dust on it. I think the coolant is coming out as a fine mist and instantly drying when it touches the hot housing and I think the source is from where the pipe is press fit into the housing, hence the concentration of dye being closer to the housing versus the hoses.

I'm certain a new thermostat housing is on going on my parts list, but I'm still open to hearing any ideas for the time being.
 
Sides of plastic radiator could be leaking, check thoroughly. I'd replace thermostat again before a new housing. Very similar situation w my 4runner. Radiator was leaking(faintly on plastic sides where the aluminium grabs)& even w a faulty thermo, it maintained normal operating temps.(toyota4runnerareamazingmachnes) I had the mist, the white powder, etc.. but not no more (new rad & thermostat)
 
I don't think I ever updated this, but it turns out the leak was coming from in between the casting of the thermostat housing and the press fit pipe that connects the hoses to the heater core. I tried to braze the area shut with aluminum brazing rod, but the thermostat housing soaked up the heat too fast and could never get hot enough the melt the brazing rod. The solution was another thermostat housing.
 
Solution
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