oil in coolant tank

billu427 · 01-16-2008, 12:14 PM

Hello everyone I have a 98 contour se 2.5dohc .I like the car but i have oil in the coolant tank and I'm pretty sure that it's a head gasket. I will probably swap the motor, but what are some of the first performance mods that most people do first. and what are some of the common problems with that engine and what should I look for in a replacement . thanks

ABE · 01-16-2008, 02:20 PM

Are you sure the oil is from the engine? It could also be from the transmission since there is a cooler in the rad. A leak in the cooler could allow transmission oil into the coolant tank.

One might expect a transfer of coolant to either engine or transmission oil, so confirm that too. Coolant will turn oil milky and cause foaming. Check your oil levels cold. If you suspect coolant in the engine oil, it is heavier than the oil and will come out at the oil drain.

A head gasket failure usually starts near the cylinder and burns the gasket (after burning through the metal ring) to the coolant channels where it results in bubbles in the coolant tanks, overheating of coolant and overflow into coolant return bottle. There is often a significant drop in compression that can be measured for each cylinder.

Good luck with the diagnosis.

billu427 · 01-16-2008, 09:07 PM

wow, thanks for the info .I suspected oil because the tank has black residue on the walls of the coolant tank. And I have to top of the coolant maybe once a week,but the car seems to run ok otherwise.But at the last spark plug change there was oil on two of the front plugs ,more so on the threads than the electrode .
so what do you think?

ABE · 01-17-2008, 02:02 PM

The dark material on the rad overflow bottle is not likely oil it is residue from the coolant. Most coolant bottles get this. Are you using the green coolant? Is it a clear green (good) or a pasty opaque green (poor and needs replacement) or a brownish green (way too old and damaging your cooling system) or brown (acids are eating the cooling system components away, should have been changed many years ago).

If there is a head gasket failure there will be bubbles in the coolant. You should be able to see them in the rad after the cap is removed (do not do this when hot or you will get a face full of steam and scalding water). The number of bubbles will increase as the failure gets worse. There will be a lot of coolant going to the overflow tank and lots of bubbles, and not all will be sucked back into the engine because of the air. Also there will be a tendency for coolant temperature fluctuations due to excess air and heat in the system. Heater system performance often suffers due to an air lock shown by heater core hoses not at same hot temperature, and the outlet to water pump is cool.

There are many places for a leak to occur:
1. Have you checked the overflow bottle for leaks in the plastic or the hose or the connections at rad?
2. Rad cap not sealing pressure in engine or at top of rad;
3. Have you checked for coolant hose leaks or loose fittings?
4. Water pump leaking?

Oil on the plug threads is more of a sign of a leaking valve cover gasket. Oil on the plug tip and electrodes is a sign of engine piston rings that are worn. Yours sounds like a valve cover gasket needs tightening slightly or replacing.

Hope this helps.

billu427 · 01-20-2008, 08:51 PM

hi ,first thanks for taking the time to reply. I recently flushed the cooling system so the coolant is fresh .I have checked many times for leaks and have found none visable. when I flushed the system I took the recovery tank off to flush it out and clean it just to see if the black stuff would return and it did. it has no leak .and I replaced the upper hose a couple months ago and can't find any other hose leaking .The cap seals tight and appears to hold pressure. Thought about the water pump too, but dont see any leaks. I havent noticed alot of bubbles in the tank or alot of fluid movement, thought there should be more? Didn't think about the valve cover thou, pertaining to the oil on the plug threads. Havn't had a chance to check them but, I will change them just to be sure, didn't think oil from the valve covers could get down there. As far as the heat goes there is a big fluctuation in temps and the gauge does move ,never goes past the m in normal but it does move, abit .Again thanks for taking the time to reply I hope it's not a head gasket, but I don't know?

ABE · 01-21-2008, 10:55 AM

If you take a look at the plug access it is right in the middle of the valve cover. The plug hole in the head is surrounded by the valve cover gasket. If the gasket is loose or fails all the oil from inside the valve cover can spill into the plug hole. Just a thought.

The water pump is enclosed on your engine and any leakage from the bearings and seals and gasket may be hard to detect below the unit. Are you sure it is dry down there?

The best place to see bubbles is with the rad cap off and watch the engine come up to temperature.

Another verification of bubbles in the cooling system is to check how full the rad is when there is coolant in the bottle. If a lot of air in cooling system then it will not draw coolant out of the bottle. So if rad is usually full when cold and bottle has correct coolant level and you don't see bubbles in rad then head gasket should be ok.

Can you smell coolant at the exhaust? That is often a sign of coolant entering the intake manifold, but would be very small if no white smoke present.

Hope this helps.

hortondeerhunter · 02-10-2008, 11:54 AM

I'm having the same issues with overflowing reservoir tank with residue and has a fluctuating temp. reading that can go to red line then drops quickly then climbs again (loss of heat when it starts climbing). I started by replacing the thermostat and sensor that regulates the fan. Then went and replaced the water pump and then the radiator. At idle while I was investigating and trying to bleed air (funnel with the radiator cap and thermostat removed plus bypassing the heater core/rear air there was no problem with circulation. All hoses were hot. When I got in and drove down the road the temp raised and the bottom hose on the radiator got cold. The overflow was full and bubbling. I have bought a new aftermarket cap and that did not change anything. I have even compression and a leak down test showed no indication of problems. Could it be Idle air control, ISC, or another sensor? Does the water jacket through the intake manifold or throttle body? Could it even be an oxygen sensor from the catalytic converter? Does the intake have coolant ports?