I've been putting up with a small coolant leak in my 89 GTU/GXL (engine has been in 2 different cars) ever since I rebuilt my engine 2 winters ago. I have tracked down pinhole leaks in hoses, fixed them, and I still lose coolant... about a quart every 2-3 weeks during the summer... depending on how much I auto-x. I'm beginning to think I might have a coolant seal leak. I've been reading every coolant seal/ coolant leak thread that's been posted in the past few months. Ive tried a few of the tests and they never show up anything leading me to believe I've got a coolant seal problem. I've also run out of hoses to check of leaks.

Reasons I think it might be a coolant seal problem:

The car smokes on start up...

The car dumped all of it coolant on the freeway through a hole in a hose and by the time I reached an exit and pulled in a gas station(like a mile and a half from where the buzzer went off) the needle on the s5 temp gauge had almost reached the top... which means it has been over heated.

Before I took the car off the road for this winter I noticed some oil floating on top of the coolant when I took at radiator cap. Also, there was white slime(from coolant and/or moisture and oil mixing) on the oil dipstick and on the bottom of the radiator cap... I cleaned that off and it hasn't returned with the driving I did before storing the car (1 auto-x and about 200 miles)

Here's what I've tried:

My car smokes on start up... It has always smoked a little on start up after sitting overnight. This smoke is white but never smells sweet like burning coolant. It always smells like its running way too rich it never smells like coolant burning. Could the fuel smell mask the scent of coolant burning? I'm pretty sure my injectors leak because I get hot start problems despite good compression... so could that be the cause of my start up smoke?

This past weekend, after my car had been sitting for a week or so without being started I pulled the EGI fuse and cranked it over. I pulled the plugs and there was a hint of moisture(which didn't smell like anything... coolant or otherwise) on the tan-ish deposits on the plug but nothing that would match up with the amount of coolant I lose.

I have tried the test where you pull the cap off the radiator fill and watch for bubbles when the engine is running. I started the car cold and let it warm up. I never saw any amount of bubbles that would lead me to conclude that the coolant seals are bad. I remember seeing one tiny bubble over the course of like 20 minutes.

The car passed a coolant system pressure test a few thousand miles after it was rebuilt at the mazda dealership. They said the coolant seals were fine. I haven't had it retested after over heating it because of the pinhole leaks I've found... Wouldn't it be impossible to tell if the seals were bad or if it was a hose causing the drop in pressure? I am planing on replacing the hoses this winter but I was going to do a soft seal rebuild too if I could be sure the coolant seals were leaking.

What else should I try while it still runs before I pull the manifold off to redo the vacuum lines and replace the coolant hoses?


Cliff notes:

Car loses coolant... some signs point to bad coolant seals... but nothing definite.

- Car smokes on start up... but smells like fuel not coolant
- White slime on dipstick, oil fill cap... small amount of oil floating on coolant
- Car has been overheated (well at least on the verge of overheating)
- no bubbles seen in coolant when car is running
- no coolant on plugs when engine is turned over after sitting for a week without being run.

So what should I check next?

Thanks,
Rob

 

Hmm..

I had a problem with the heater hose just this weekend, it ripped on me and i lost a lot of coolant that way and i think that is what caused me to loose coolant and get air bubbles in my cooling system. I almost OVERheated my engine (It did heat up pretty good about half way on the S4 temp gauge). Have you checked that? The heater hose is located on the Spark Plug side of the engine. It's a hose that leads from the engine to the firewall. Examine it and see what you find.

Josh

 

Well, definately sounds like bad coolant seals to me. If its not dripping anywhere, there's a good chance you are burning it. How many miles on this engine?

 

Even tiny coolant seal leaks would cause at least a few bubbles to form, especially if you rev the engine with the rad cap off.

Are you sure it isn't a small external leak? Die kits can be used to find small leaks like that easily.

 

It could be a small leak in one of the hoses. I just figured that with the amount of coolant I lose I would at least see some of it on the ground... but if it only leaks under pressure and it hits hot parts and evaporates that might explain why I never see any on the ground. I'll have to track down some of that fluorescent die and see if I can find a leak.

 

I've Had this hose go bad on me... thats how I lost all my coolant on the freeway... it had a big rip on the engine side. I fixed that in the parking lot of the gas station. I cut off the end at the hole and it hasn't given me any trouble since... But I'll check it to see if it's leaking at all. That hose is on the list to replace this winter.

 

10,000 miles since the rebuild... rebuilt at 104,XXX miles.