have an 87 omni,what would cause back pressure in the cooling system ?

Asked by Aug 24, 2013 at 01:55 PM about the 1987 Dodge Omni

Question type: Maintenance & Repair

have antifreeze pushing out of the overflow on the radiator

4 Answers


Gee I thought all of those had died out, you are describing the typical blown head gasket problem.


Nothing good. A little bit of antifreeze flowing back to the tank is alright but lots is not good. If it is excessive I would lean towards (or hope) the head gasket. Compression from a (the) clyinders is entering the coolant system and pressuring it up. Worst case It could be a cracked head or engine block. Check and/or drain your engine oil. If there is no water in the oil it should only be the head gasket. If there is then it is probably easier to source a used motor.


An '87 Omni with a blown head gasket! What are the chances?


As aforementioned, excessive pressure in the cooling system is usually typical of a blown head gasket. The head gasket is what seals the upper and lower halves of the engine together. When it leaks, you get combustion gases forcing their way into coolant passages, coolant being burned in the combustion chamber or oil mixing with the coolant (or any combination thereof). The motor can be evaluated with a compression tester (a gauge that screws into the hole where spark plugs go) and determine if the gasket is leaking combustion gases into the cooling system. This is a quick and relatively easy test, most gauges come with basic directions. Remove all four spark plugs. Disable the ignition system so the vehicle cannot start by removing the coil cable from the centre of the ignition cap and ground it to a point on the chassis out of the way. Screw the compression tester into the number one cylinder and with the aid of an assistant, have one person check the gauge while the other cranks the engine over. Open the throttle wide open while cranking. Let the motor turn over for several compression cycles and watch the gauge. It should shoot up fast and eventually stabilize at a reading. Most engines read between 140-150 psi(g). Repeat this for all cylinders. The difference between the highest and lowest reading should be within 10% of each other. If one cylinder is very low or if two adjacent cylinders are low it is usually indicative of a blown head gasket.

1 out of 1 people think this is helpful.

Your Answer

Add photo

Related Questions

  • need diagram of 1989 Dodge Omni steering system 1 answer

    need to change the tie rod

    1989 Dodge Omni


    Maintenance & Repair

  • Cooling system 1 answer

    So my truck would randomly overheat and then drop back down. So o changed the thermostat. Now it still does it when I'm driving normally and if it starts to do that and I increase the rpm to over ...

    1997 Dodge Ram 1500 2 Dr ST 4WD Extended Cab SB


    Maintenance & Repair

  • What are some causes of oil pressure loss? 33 answers

    Losing oil pressure but it comes back. Could it be a sensor or is it a bigger problem?

    2001 Dodge Ram 1500 4 Dr SLT Plus 4WD Quad Cab SB


    Maintenance & Repair

  • Where do I get a pressure test on my coolant system? 1 answer

    Having signs of cooling system problems, such as overfill empties after a few short trips and temp. needle goes up and down while in travel. Seems to go hotest sitting at stops.

    1988 Dodge Aries


    Maintenance & Repair

  • Cooling System Pressure Problems 3 answers

    All pertains to a 1985 Jeep CJ7 2.5L 4clylinder: About a month ago 2 leaks broke out in my cooling system. One around the water pump the other was a freezer plug. I replaced the water pump and repla...

    1985 Jeep CJ7


    Maintenance & Repair


Looking for a Used Omni in your area?

CarGurus has 2 nationwide Omni listings and the tools to find you a great deal.


Search Dodge Omni Questions

Dodge Omni Experts

#1 TheCanadian007
Reputation 150
#2 Chris McGee
Chris McGee
Reputation 40
#3 msmsls
Reputation 30
View All

Related Models For Sale

Used Volkswagen GTI
89 Great Deals out of 5,877 listings starting at $2,000
Used Dodge Charger
248 Great Deals out of 27,253 listings starting at $1,790
Used Buick Regal
94 Great Deals out of 10,213 listings starting at $3,495

Used Cars For Sale