1991 f150 4.9 EFI



I just wanted to check this with people who know more about engines than I do. I just took the truck to the mechanic for what I thought was a blown head gasket (coolant in oil) he turned around and told me he did the compression test with the highest cylinder at 152 psi and the lowest at 125 psi. He said he did a test to see if there was leakage past the rings. Which he said there was. This is where I don't understand engines I guess but I have no smoke,acceptable compression,coolant in oil and he says I have a ring problem in cylinder 6 which means I need a new engine.

Does this sound right? It might be,as I said I don't really know much about engines.

Thanks for any imput.

 

Ford's compression spec. is the lowest cyl. must be 80% of the highest cyl. By your post the highest was 152, the lowest was 125. 80% of 152=121.6 which means comp. is right on spec.

Doing a cylinder leakage test and finding leakage in only one cylinder hardly requires replacing the motor. If anything a ring job is what's required.

But by your post the engine doesn't smoke and I assume runs OK. Hardly symtoms of an engine at the end of it's life. Leakage past the rings won't cause coolant in the oil, it will allow exhaust gasses to blowby the rings, reducing power in that cylinder. If you find the oil getting dirty sooner than it used to that's a result of blowby.

By my experience your right on target by suspecting the head gasket. That will cause coolant in the oil, as well as low compression because there is no seal at the top of the cylinder.

Good luck.
Hope this helps.

 

exactly as ^ said, VERY suspicious of a bad head gasket, which on the 6 cyl. would be a relatively easy job. Anytime you get coolant in the oil, be suspicious of a bad head gasket.

How many miles on the truck? By the look of the compression numbers, they dont look bad. And always go get a second and even third examination of your truck, dont trust one mechanic to tell you whats wrong, especially (no offense), if your not too informed about your truck. If it turns out to be a bad gasket, it wil be worth the $$ to have it fixed. Those old inline 6's run are tough.

Post your results and what it ends up being. Good luck!!

 

I had a 1993 F-150 with the 4.9 inline 6 and 5 speed manual. That thing was bullit proof, I traded it in with 198,000 miles, no major work done, except a new radiator, and some minor tranny work. IMO That was fords best engine, for durability.