The fans work (high and low), coolant level is completely full and I'm not losing any coolant, nothing is blocking the radiator. I am using Evans coolant and I have a Mezzier Elec water pump and a 160* thermostat.

After driving on the highway for about 15 minutes the temp gauge sloooooowly climbs to 210, then it jumps to 230+. I let off the gas and slow down and it falls back to around 210 or so. As long as I drive under 50 mph it stays around 210.

This just started happening. My gauge always read well below 210. All I can think of is a bad thermostat or my electric water pump is going bad. Any other ideas?

 

Check the plastic air dam under the front end, if it's missing it can cause the symptoms you're describing

 

I too have a Meziere. Make sure none of your electrical connections are loose. You may have a pump that working intermittently.

I agree with the above, make sure your air dam is intact. If it isn't then adequate air isn't being routed over the radiator at higher speeds (more rpms, more heat).

 

I would check the thermostat. Perhaps the water pump.

Highway driving should cool the car down, more air under the car cools the engine, if I'm slowly driving around town the fans will come on, bay neve ron the highway. I too have the 160* stat, had no problem, my gauge always sits below half way.

Another thing to check is O2 switching, i know it sounds crazy at first, but if you are running too lean, then it will get hotter. Its just another thing to check if you can.

 

I know I'm not running lean. I have a LC1 wideband. Stays around 14:1 on the highway. That's fine for part throttle.

This started after a heads/cam install. We also installed a double roller timing chain and I also deleted my PCV and installed breathers on both valve covers. I don't know why any of these things would cause my problem though.

 

There are 4 coolant pipes for the heads, are these okay, are they like stock?

I've plugged my rear ones, the front ones are required to link to each other and run to the rad.

Perhaps you still have some air in the coolant system. Run it on tick over with the rad cap off, perhaps squeeze some of them large water pipes, watch out that you don't get caught in the fan.

I don't have any experience in the electric pump, perhaps 'allngn_c5' has a valid comment.

 

Are you talking like the temp drops in a matter of seconds after slowing down?

 

are the head gaskets in correctly?

 

Well I commented earlier. Your pump may not be on all the time due to a loose wire. I am a little dumb struck. My Meziere only has 4000 miles of driving on it and the weather did test it to see what she could handle. The worst conditions it had to deal with were 100+ degree temps and bumper to bumper traffic. Coolant never got above 200 degrees or so. Did I mention the A/C was on full blast? I was impressed. In stock trim under the same conditions temps would stay around 230 or so and take forever to cool down. Both fans running and temp staying at 230. Hate getting caught in bumper to bumper traffic on a hot day.

Check all connections, and even check the fuse for your Meziere, you may be maintaining engine temp soley with the cooling fans if your fuse is blown. Do you hear the electric motor of the Meziere when you turn the key to on? I could be wrong. Ask one of the local performance shops. They will have a better idea.

 

The pump definitely comes on when I turn the key on.

Yep. Like I said, it slooooowly climbs to 210 (takes like 5 or 10 minutes), then it takes another couple minutes to go a hair past 210, then in a matter of 1 or 2 seconds it shoots up to 230+, then as soon as I let off the gas and slow down to 45 or slower the temp falls back to 210 in a matter of 2 or 3 seconds. As long as I go slower than 50 it stays at 210 or 215.

My mechanic is stumped. So am I.

 

There's no way heat could be removed from the engine that fast. I think you've got an electrical problem. I'd be checking the sensor/sender and the gauge cluster. I had a fan problem on my LT1 once and it would cool fine out on the highway but as soon as I started stop and go traffic, it would start climbing. Get back on the highway, the engine would only cool maybe 5-10 degrees even though it climbed 50 in traffic. The one fan running and the electric pump moving and all the airflow at 60 mph could not cool it back down. It would stop it from getting hotter, but it couldn't cool it. I put my laptop on it when I got home and with the car off and electric pump on, it would only cool a couple of degrees every 2-3 mins. So I am fairly confident that your car cannot cool 25 degrees in 2-3 seconds.

 

I don't know about that. If coolant were to suddenly stop flowing and then start again that could cause a rapid climb and even fall in temperature. This has happend 3 times now. Same thing every time. It takes about 15 or 20 minutes of highway driving with temps rising about 1 degree every minute. Then when engine temp gets up to about 215 the gauge climbs to 230+ in a matter of 1 or 2 seconds. I let off the gas and the temps fall back to 215 or 210. My car always ran 180 to 190 degrees prior to this problem. So even 210 is very high for my car.

 

Have you changed the T-Stat ?? Sounds like the most simple check and see thing to do. You may have a sticking STAT, or at least some malfunctions. Good luck.

 

Just a though.. have you check your radiator...? plugged ?.. (dexcool), maybe flush the system and refill and make sure you get all of the air out of the system.. fill the engine directly in from the top radiator hose.. then reconnect and finish filling the system.

 

Just seems really odd to me. I just don't think it can cool that fast just by slowing down. But regardless, tackle it however you choose and good luck trying to fix it. I know how frustrating it is trying to find problems like this.

 

Do you have a scanner...the guage is wrong or should I say off. My car runs at 192 or 193 and the guage says 210. I check mine with HPTuners and I think maybe your thermostat is sticking or you have one or both of your head gaskets occluding some water holes...as speed/load increases the engine is producing more heat and limited flow like that will make the engine heat up and when you let off it will cool.

Just my $0.02

 

My gauge is accurate. I know some are not but I have logged engine temp many times and the gauge is spot on.

The head gaskets are .040 Cometic. I'd be surprised if they were not designed right.

 

occluded= to restrict
Basically he's thinking the coolant passages are partially blocked by the gasket, restricting the flow

 

Yeah I looked it up and edited my response at the same time you replied.

 

My car started to run hot one day out of the blue, for NO reason at all. My car normally runs ~185 (1998 working gauge here) with my manual fan switch on ALL the time. It started to run up about 200 and then 210 and I thought for sure that the fans were not working properly.

I thought to myself "I might change the T-stat and coolant first" and sure enough, the car started running back at normal 185 again...