Jump to content
BigKeyserSoze

Need help diagnosing SM engine death this weekend

Recommended Posts

BigKeyserSoze

The car is a 1995 1.8L Miata.

 

On Saturday, my Miata blew up 3 laps into the opening morning practice. It started losing power, and people on track told me it was blowing smoke on the shifts, and then just generally blowing smoke later. By the time I got it off track, it was dead, and smoke was coming from everywhere. After it shut off, it would no longer start.

 

What happened was the radiator had a hole and drained, so the car went without coolant. The gauge temp never went up, since there was no coolant on the sender. The car had plenty of oil, and the lack of water was definitely the cause of the problem.

 

I ran a compression test tonight, cold engine, throttle blade closed: Cylinder 1 - 30psi, cylinder 2- 10psi, cylinder 3 - 10psi, cylinder 4 - 30 psi. So we know something is wrong with all 4 cylinders.

 

Here’s the funny part. I pull the head (aluminum) off tonight, and the block (iron), pistons, head gasket and head all look fine. I did notice that the coolant temperature sensor, which lives in the back of the head, was literally melted and has been blown out of its threaded hole.

 

The cylinders are not noticeably scored. The pistons slide in the bore nicely and the engine will turn over by hand.

 

So, what went wrong? Can you literally overheat an aluminum head so bad that it warps and will not make cylinder pressure? Can the valves or the valve seat be so screwed up that the same problem happens? It seems to me its either the head or the top piston rings all are dead. I’m trying to diagnose if the block needs to come out and be serviced, or if I can just have the head rebuilt.

 

Thoughts?

Share this post


Link to post
Share on other sites
jblaisdell

Please send this post to:

[email protected]

and/or call him 336-595-3413

Talk to an expert!!!

Share this post


Link to post
Share on other sites
Ole

Warped head! Take a straight edge and place it along the top of the head, you will see a slight difference. Then place it along the bottom and see again. Throw everything out, nothing on the head is salvageable. Go through the bottom end and replace all bearings and rings...you should be ok based on your findings of no cyl scoring. You might even be able to get away with no rings, but if you have the engine that far apart, you may as well go ahead and replace them CHECK EVERYTHING on teardown before you re-use anything. If in doubt, replace it.

Share this post


Link to post
Share on other sites
Dirt Surfer

Sounds like you look all of the temper out of the rings also

Share this post


Link to post
Share on other sites
Dirt Surfer

You may need to replace the rings also, if it got that hot it may have taken the temper out of them, but given the statement about the scarring in the cylinder walls it sounds like a complete rebuild is necessary. Also if it warped the head badly it can throw off the Cam Bosses in that you will be burning up cam bearings after a rebuild. I'd replace it.

Share this post


Link to post
Share on other sites
jc8587

I'd hope he has fixed this already... Oct 2011...

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...