I have an 85 Bronco 351w HO 200K on engine. When the engine is cold in the morning, the oil pressure is high, but after it gets heated up real good it drops down. Yesterday I was sitting at a light and the pressure gauge dropped to nothing and the temp gauge started to go up. When I gave it gas, the oil pressure gauge went up again. It did the same thing today also. If it is idling, the needle drops down. I replaced the sender and it still happens. Is this anything to worry about or is it normal.

Dan

 

Hmmm, usually I blame the gauge or sender, but in this case when your Oil Pressure went down the Temperature went up. So unless they are electrically related and you coincidentally get a rise in temperature with a drop in pressure, you probably do have a problem.

If you are not circulating oil, you at best are losing it's cooling effect, ie oil does more than just lubricate. Also the temperature will rise because metal parts are starting to rub, really bad. You need to find out what is causing the problem. Did your oil pressure just recetly start to drop to zero at idle or has it been slowly dropping over a long time? If it is recent that would lead me to lean towards some component failing and causing a drop in pressure. Maybe the Oil Pump pressure spring has finally died or gotten weak. I am not sure on Fords, but most pumps have a spring which controls pressure, they do fail after time and often heat will cause them to loose their temper over a long time.

Maybe a seal has started to leak. Maybe the bearings are finally getting too loose to maintain pressure.

An engine with 200,000 miles has done pretty good, and you can't blame it for starting to show signs of old age.

Maybe the pickup tube is clogged or has a crack or leak and is sucking air.

Whatever is causing the pressure to drop is probably a real problem which needs to be fixed, if it isn't already too late. That temperature rise really bothers me, it is not a good sign.

You need to figure this out relatively soon, Good Luck.

Jim Henderson

 

Hmm, about 4 months ago I had no problems, the oil pressure gauge would stay pretty close to the middle. Over the past few months, the oil pressure just kept dropping a little at a time until yesterday when it went right down. I have a pretty big oil leak which I can't find. It's not the oil pan gasket or valve covers and it looks too high up for the rear main seal, but I'm losing a quart every week. I was just going to let it leak, but if it is causing me to lose pressure I will have to find it. Could that leak cause it? - pressure is great when it is cold and gets up to between the n and o on normal on the gauge when I rev the engine up real high - 70-80mph. Maybe I'd better take the cell phone with me tomorrow.
Dan

 

Hi, I had a 302 that did the same thing with 162,000 miles on it and it was bad main bearings when it is cold the oil is thicker and it will stay in the bearings but as it heats up it gets thinner and runs out of the bearings and when they have that many miles on them they are just too loose to keep pressure. I would try putting a mechanical gauge on it just to see what is happening but it looks like it could finally be time for a rebuild. John

 

You said that the temperature started going up while sitting at a red light. This in itself is not unusual (less air flow through radiator). At 200,000 miles, I agree with the others about the bearing wear most likely being the problem. Does it sound like someone beating on a hollow concrete block with a hammer for a couple of seconds when you first start it in the morning? Good sign of main bearing wear. The 302's and 351 Windsors used to be bad for this, but they would still run forever. As far as the leak causing the low pressure, this is not likely because about the only thing that would do this would be the sender, which you have already replaced. If you want to put a "bandaid" on it until you get time to rebuild, you might go to a heavier oil. (Some of the heavier synthetics, (such as 5W50) help, but probably not very economical if you have a leak.)

BillyO

 

An oil leak too. You say it isn't the valve covers and seems too high for the main seal. Where is the oil coming out of, is it coming out of the bell housing or is it on the outdide of the engine? If it is coming from inside the bellhousing, I would suspect the main seal or very possibly one of the oil galleries has started to leak.

I don't know about 302 engines, but many other brand X engines have some plugs at the back of the engine. They will either be threaded or like freeze plugs. Often there will be two small ones one on each side of the back of the engine for the lifter gallery and one right in the middle of the back, the camshaft plug(usually a freeze plug type). If they are leaking you will need to pull the tranny to get at them.

If the leak is outside of the bell housing it may be a head gasket. A leaky head gasket can cause oil loss and low pressure without any water loss BTW, I had this happen on a Tbird I owned. You will need to clean things off enough so you can see where the leak is coming from. Alternatively it is common on Chebbies, I don't know for sure on the Ford, for the intake gasket to leak, getting oil on the back of the engine and often looking like it might be a main seal leak.

If you are losing a quart a week and having low pressure you do have problems and they may be related and getting worse. As you mentioned you have had this leak for awhile, perhaps the hole has gotten big enough now to cause a drop in pressure, but then I would think the leak would also seem much bigger, is it?

The more I think about it though, a leak would NOT drop the pressure to zero unless you were very low on oil or had a really big leak. So I am gravitating back to bearings(slow and steady decline over time) or a cracked oil pickup(slow decline over time with perhaps a sudden turn for the worse) or maybe still the head gasket(makes a mess and if it leaks internally it could drop pressure pretty seriously). Maybe the pump gears are going bad and finally got to the point where they can't keep up or maybe the pump drive is slipping.

Whatever it is you do need to check pressure with a real gauge but I suspect you are in for at least pulling heads or it is time for a rebuild anyway.

GoodLuck.

Jim Henderson

 

Low Oil Pressure & High Water temperature are connected. One will cause the other.

Check to make sure that you have plenty of coolant and oil. Being low on either one will aggravate the problem.

 

Thanks for all the ideas. I did not know oil could leak from the heads. It is dry right above where the heads meet the block, but below, the engine is covered with oil on the back sides. I guess it is time for a rebuild, but I don't have the time to do it myself now or the money to have it done. If it will hold together for a month and a half, I'll be ok. I guess I'll get some thicker oil and see if that helps it. Any other ideas to keep it running for a little while longer? Thanks,
Dan