i have a 87 f 350 with a 6.9 diesel an i just had the oil changed then didnt drive it for about a month....out of nowhere the oil pressure reads on the low side now and the engine light comes on at idle...never did this ever..when i rev it the pressure goes up...some one help mee i dont want to kill my motor it runs soo welll

 

Could be just a oil sender failing, pretty common place for the early 6.9/7.3, but should be checked with a mechanical gauge to verify a spec pressure...

 

ok do you know where the sender miight be...would it be better to just get a mechanical guage an forget about the stock one..im just nervous to drive like that

 

Sender is mounted at the back of the engine, behind the intake towards the top of the bellhousing/engine rear area.. Was pretty common for the engine vibs to cause a sender to fail for gauge indication, or cause the sender to bleed.. Sender is cheap, and a replacement might be a quicker test, and/or fix.. Although a mechanical guage would be a 'best' test/check if your concerned, and would give a real life pressure indication over the OEM unit...

 

ok thanks alott im gonna buy the mechanical one..do you know wat the oil pressure should be at..im not good with diesels

 

The 6.9 has a 1/8 pipe plug in theoil galleryon the left side/rear of the block directly behind the drivers side exhaust manifold, directly inline with the lowest trans mount bolt.. Pressures are going to varydepending on miles, engine oil, and temp ect.. A good pressure concidering age, mileage would be about 40PSI at cruise RPM.. I think spec was 40 to 70 psi at 3300 rpm.. You may see some low numbers at hot idle, could be 10-15PSI or so for a vintage 6.9..

 

ok soo heres the newest issues i noticted the guage is fine for the first 30 min of driving..then outta nnowhere it goes down only at idle...or when im not giving it gas also the temp guage doesnt really work...im starting to think this is a electrical problem