Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.


High oil pressure & Overheating

High oil pressure & Overheating

Long story short; My '89 Sportster 1200 recently overheated when I left it idling too long. Ran like a dog when I go back on, coughing & spluttering. Turned it off and oil came spilling out of the carby air filter cover (presumably from the vent hose). Changed oil & filter; cleaned out carby/filter etc. and took it for a run.

Runs fine but since then, engine runs a lot hotter than before and every time I switch it off there is a small oil discharge from the carby air filter and I can see traces of oil that has pushed out of my oil tank cap whilst riding. Any ideas?

RE: High oil pressure & Overheating

You may have lunched a piston. Check compression and leakdown on both cylinders.

RE: High oil pressure & Overheating

Maybe not killed the piston but just stuck or broken a ring. Either way, start with the compression and leakdown tests.


The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: High oil pressure & Overheating

Thanks Guys,
I was hoping this wasn't the case as I recently pulled down the whole top end and replaced cylinder rings, seals & gaskets, also replaced clutch/pressure plates & stator. Didn't want to pull it down again but I guess I may have to.

I will run compression/leak down tests first. Thanks again. I'll let you know the outcome when I can manage it.

Cheers, Paddo

RE: High oil pressure & Overheating

Maybe consider something with a cooling system?poke


The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: High oil pressure & Overheating

Rear cylinder cooling design sub par . And there ends the nice things I can say. nosmiley

RE: High oil pressure & Overheating

If you're lucky, maybe you can bore it out and fit bigger pistons and rings.
If you're not so lucky, you'll need new jugs too.

Mike Halloran
Pembroke Pines, FL, USA

RE: High oil pressure & Overheating

Almost sounds like something's up with the timed breather. Does your model year have it?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: High oil pressure & Overheating

How did it run with the fresh top end, before the overheating?
How many miles on the fresh top end prior to overheating?
What was the condition you used to identify the overheating?
How long was the "too long" idling time?

I'm not sure I read a symptom I'd relate to high oil pressure.

RE: High oil pressure & Overheating

Seems to me like the rear cylinder should cool about as well as the front one at idle.

RE: High oil pressure & Overheating

... or as poorly, depending on your point of view ...

RE: High oil pressure & Overheating

Thank you all for your feedback.
To answer some questions:
Leak-down test 15% on front cylinder = OK; 40% on rear cylinder = problem
Pulled down top end again and currently inspecting rear piston, cylinder & rings
Next Action:
Hone both Cylinders
Replace both Piston Heads
Replace Rings again
Put together and perform leak down test again................

RE: High oil pressure & Overheating

Thanks for the tips Tmoose,
I have not had a chance to get back to it to inspect since pulling it back down. I might not replace the piston heads but am prepared to if there is any doubt of their integrity.
Getting back to your original questions - 1) It ran perfectly with the fresh top end for over 6 months before the overheating incident; 2)Approx. 3,000 miles.
3) Running a lot hotter than previously. I could physically feel it and it was now making excessive crackling (cooling down) noises when turned off after a run.
4) It was idling for about 20 minutes on the side of the highway at night as I used my headlight to get my wet weather gear on. I noticed it started smoking so I just jumped on and took off down the highway in the rain. This is when it was coughing & spluttering and severe loss of power. I pulled into a service station and killed it which is when the oil came spewing out of the carby air filter. I let it cool down for about 2 hours, cleaned it up, then hit the road again. It continued spluttering for about 5 minutes then started running normally again, however at every stop - small amounts of oil would spit out from the air filter and a light stream was apparent from around the oil cap.
When I got the bike back home (350 miles later) I changed the oil/filter to eliminate contaminated/burnt oil. It continued running fine but with the oil pushing past the oil cap whilst riding and the spurt of oil from the air filter when stopped, plus the excessive engine heat. That's the long story.............

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close